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Carcinogenicity

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Description of key information

Formaldehyde has local carcinogenic activity in experimental animals; there is evidence for a threshold effect for tumors involving cytotoxicity and regenerative cell proliferation as the mode of action.
There is no evidence for systemic or local carcinogenic effects after oral exposure in rats. In dermal initiation/promotion studies formaldehyde did not initiate or promote skin tumorigenesis in mice. There is clear evidence from chronic inhalation studies in rats that formaldehyde causes tumors in the nasal cavity.
The results from epidemiological studies are highly contested but may suggest an increased risk of cancer only at two tumor sites: nasopharyngeal cancers (NPCs) and leukaemias. The most recent review covering both relevant endpoints (Bachand et al 2010) concluded that summary risk estimates for NPCs were not elevated after excluding a single plant with an unexplained cluster of NPCs. Moreover, the most influential epidemiological study, i.e., the NCI industrial cohort study that includes this cluster plant (Hauptmann et al 2004) is unreliable regarding NPCs because of a missing robustness and an incomplete vital status follow-up (Marsh et al 2007a, Marsh et al 2007b, Marsh et al 2010). Bachand et al 2010 concluded about leukaemia risk: “By limiting analyses to stronger case-control and cohort study designs, considering the effects of smoking, these meta-analyses provided little support for a causal relationship between formaldehyde exposure and leukaemia.” Furthermore, current analyses of the NCI cohort (Beane Freeman et al 2009a) did not confirm the statistically significant exposure-response relationships between formaldehyde exposure and leukaemia mortality reported before (Hauptmann et al 2003).
The studies from 2009 up to 2015 did not strengthen an association between formaldehyde exposure and NPC or leukemia.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Referenceopen allclose all

Endpoint:
carcinogenicity: oral
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
Study meets scientific standards with acceptable restrictions concerning initiation/promotion in forestomach and glandular stomach; not valid concerning formaldehyde control (low number of animals, short treatment period, one dose level [clearly irritant]; possible confusion between papillary hyperplasia and papilloma in the stomach; partly limited documentation, e.g. no details about test substance).
Principles of method if other than guideline:
Oral initiation-promotion study in forestomach, glandular stomach and duodenum of male rats using N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)plus NaCl for initiation and formaldehyde for promotion.
GLP compliance:
not specified
Specific details on test material used for the study:
Source: Wako Pure Chemical Company
no further data
Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals and environmental conditions:
7 weeks old at initiation
5 rats/cage
housing conditions: temperature 21-25°C, 50-60% rel air humidity, light dark cycle 12/12 h
no further data
Route of administration:
oral: drinking water
Vehicle:
water
Details on exposure:
Group 1
initiation without promotion: 100 mg/L MNNG in the drinking water (ad libitum) plus 10% sodium chloride in the diet (ad libitum) for 8 weeks
Group 2
Initiation like in group 1 plus promotion: 0.5% formaldehyde in the drinking water (ad libitum) for 32 weeks
Group 3
No initiation but 0.5% formaldehyde in the drinking water (ad libitum) for 32 weeks
Group 4
concurrent no treatment
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
initiation 8 weeks, promotion 32 weeks
Frequency of treatment:
drinking water and diet ad libitum
Post exposure period:
no
Dose / conc.:
0.5 other: %
Remarks:
nominal concentration in drinking water; ca 450 mg/kg bw/day
No. of animals per sex per dose:
Initial 30 rats in Group 1, 20 in Group 2, 10 in Group 3&4
Control animals:
yes, concurrent vehicle
Details on study design:
Screening study with several substances tested for promoting activity
Observations and examinations performed and frequency:
Clinical signs recorded daily
Body weight measured every 4 weeks
Sacrifice and pathology:
Necropsy of all animals at termination and rats found dead or moribund
all rats surviving up to week 30 (termination week 40) were included in evaluation of effects in forestomach and glandular stomach
Histopathology of forestomach and glandular stomach
Other examinations:
no
Statistics:
Fisher exact test
Clinical signs:
not specified
Description (incidence and severity):
no data
Mortality:
not specified
Description (incidence):
Early deaths of 3 rats in Group 2 (initiation plus promotion)
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
clearly reduced body weight during initiation; reduced weight gain also in rats receiving 0.5% formaldehyde in the drinking water (data from graph).
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Formaldehyde induced erosion and ulcer at the limiting ridge of the fundic mucosa.
Formaldehyde exposure with and without prior initiation resulted in "papilloma of the forestomach" (incidence 88 and 80%, respectively); no such lesions were found in untreated rats or in initiated rats without formaldehyde treatment (see comment below).
In initiated rats the promotion with formaldehyde increased the incidence of hyperplasia in the glandular stomach in comparison to rats receiving only initiation with MNNG (see comment below).
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
The incidence of adenocarcinoma of the pylorus part of the glandular stomach was increased after promotion with formaldehyde compared to initiation only group. No adenocarcinoma was found in the fundus. However, adenocarcinoma of the duodenum was decreased in formaldehyde treated animals; these tumours were detected "within 10 cm of the pyloro-duodenal junction". Combining the adenocarcinomas of the pylorus and the pyloro-duodenal junction there was no significant (Fisher exact test) promoting effect of formaldehyde (4/30 [13%] adenocarcinomas in the initiation only group versus 5/17[29%] in initiation/promotion group).
Details on results:
No data about clinical signs.
Early deaths of 3 rats in Group 2 (initiation plus promotion)
Body weight: clearly reduced body weight during initiation; reduced weight gain also in rats receiving 0.5% formaldehyde in the drinking water (data from graph).
Formaldehyde induced erosion and ulcer at the limiting ridge of the fundic mucosa.
Formaldehyde exposure with and without prior initiation resulted in "papilloma of the forestomach" (incidence 88 and 80%, respectively); no such lesions were found in untreated rats or in initiated rats without formaldehyde treatment (see comment below).
In initiated rats the promotion with formaldehyde increased the incidence of hyperplasia in the glandular stomach in comparison to rats receiving only initiation with MNNG (see comment below).
The incidence of adenocarcinoma of the pylorus part of the glandular stomach was increased after promotion with formaldehyde compared to initiation only group. No adenocarcinoma was found in the fundus. However, adenocarcinoma of the duodenum was decreased in formaldehyde treated animals; these tumours were detected "within 10 cm of the pyloro-duodenal junction". Combining the adenocarcinomas of the pylorus and the pyloro-duodenal junction there was no significant (Fisher exact test) promoting effect of formaldehyde (4/30 [13%] adenocarcinomas in the initiation only group versus 5/17[29%] in initiation/promotion group).
Relevance of carcinogenic effects / potential:
There is no clear evidence for promoting activity of formaldehyde in the drinking water at a concentration of 0.5% inducing non-neoplastic lesion in forestomach and glandular stomach.
Dose descriptor:
dose level: non-effective dose level for promoting activity
Effect level:
5 000 mg/L drinking water
Based on:
test mat.
Sex:
male
Basis for effect level:
other: (0.5% in drinking water, one dose tested); no increase in malignant gastroduodenal tumours compared to initiation alone

Effects of oral formaldehyde in the drinking water of rats on incidences of lesions in the forestomach, fundus and pylorus of glandular stomach and anterior duodenum with and without initiation by oral MNNG and sodium chloride 

Incidence

Only initiation

Initiation & promotion with 0.5% FA

No initiation but exposure to 0.5% FA

No initiation and no exposure to FA

Forestomach “papilloma”

0/30

15/17**

8/10**

0/10

Adenomatous hyperplasia in fundus

0/30

15/17**

0/10

0/10

Adenocarcinoma in pylorus

1/30

4/17*

0/10

0/10

Hyperplasia in pylorus

7/30

7/17

0/10

0/10

Adenocarcinoma in duodenum

3/30

1/17

0/10

0/10

FA: formaldehyde; *: significantly different from initiation only, p<0.05; **: p<0.01 

Conclusions:
In rats oral exposure to 0.5% formaldehyde in the drinking water induced local lesions in stomach.
Executive summary:

Study meets scientific standards with acceptable restrictions concerning initiation/promotion in forestomach and glandular stomach; not valid concerning formaldehyde control (low number of animals, short treatment period, one dose level [clearly irritant]; possible confusion between papillary hyperplasia and papilloma in the forestomach; partly limited documentation, e.g. no details about test substance).

In an initiation/promotion study male Wistar rats (n=10-30) were initiated with 100 mg/L MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) in the drinking water (ad libitum) plus 10% sodium chloride in the diet (ad libitum) for 8 weeks followed by promotion for 32 weeks with 0.5% formaldehyde in the drinking water (n=17 for evaluation). Additional control groups received only initiation (n=30) or only 0.5% formaldehyde (n=10) or only vehicle (n=10). All groups were sacrificed after 40 weeks. Body weight gain was decreased in all treatment groups compared to vehicle control suggesting toxic effects of initiation and promotion procedure. In accord with other long-term drinking water studies local lesions in forestomach (papilloma, erosion and ulcer at the limiting ridge of fundic mucosa) and glandular stomach (hyperplasia) were induced by formaldehyde but no malignant tumours. Promotion in initiated rats increased hyperplastic lesions in the glandular stomach but did not significantly increase the total number of adenocarcinomas in the gastroduodenal epithelium. Conclusion: In rats oral exposure to 0.5% formaldehyde in the drinking water induced local lesions in stomach but there was no clear evidence for promoting activity.

Endpoint:
carcinogenicity: oral
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
Deviations:
no
GLP compliance:
yes
Remarks:
(TNO)
Specific details on test material used for the study:
- Lot/Batch number
UN2213 (Celanese Chemicals, USA)
- Specification: Paraformaldehyde prills 95% plus 5% water
Species:
rat
Strain:
Wistar
Sex:
male/female
Details on test animals and environmental conditions:
- Source: TNO central institute for the breeding of laboratory animals, Zeist, Netherlands
- Age/weight at study initiation: 5 weeks old / no data on body weight
- Acclimatization period 9 days;
- Housing condition:
rats kept 5 per cage; diet and tap water ad libitum; temperature 20-24°C, rel. air humidity 40-70%, 12 h light/12 h dark.
Route of administration:
oral: drinking water
Vehicle:
water
Details on exposure:
Fresh solutions prepared once weekly. Glass bottles filled daily and cleaned once weekly.
Analytical verification of doses or concentrations:
no
Duration of treatment / exposure:
Up to 105 weeks (interim sacrifice after 12 or 18 months)

Frequency of treatment:
Drinking water daily ad libitum
Post exposure period:
No
Dose / conc.:
5 mg/kg bw/day
Remarks:
(target dose); 0.002% in water
Dose / conc.:
25 mg/kg bw/day
Remarks:
(target dose); 0.026% in water
Dose / conc.:
125 mg/kg bw/day
Remarks:
(target dose); 0.19% in water
No. of animals per sex per dose:
70 m and 70 f per dose; subgroups of 10 rats/sex/dose killed 12 or 18 months after start of exposure.
Control animals:
yes, concurrent vehicle
Details on study design:
Concentrations adapted in weekly intervals to changing body weights up to week 52. Average concentration: 0, 20, 260, or 1900 mg/L (0, 0.002, 0.026, or 0.19% in water).
Positive control:
No
Observations and examinations performed and frequency:
- Observations: Clinical symptoms, mortality, food and water intake, body weight (once weekly), haematology, clinical chemistry, urinalysis.

- Clinical signs
At least once daily each rat was observed for clinical signs.
- Mortality
See clinical signs.
- Body weight
Measured once weekly in the 1st 12 weeks starting day 0. Thereafter once every 4 weeks.
- Food consumption
Calculated for each treatment week during the 1st 12 weeks; thereafter over 2-week periods every 3 months .
- Water consumption
Calculated for each treatment week.
- Ophthalmoscopic examination
observations of cornea, conjunctivae, sclera, iris and fundus oculi made in all rats of the control and top-dose groups at week 0, 52 end 103
- Haematology
In week 26 and 103 blood samples of 10 rats per dose per sex were taken for analysis of haemoglobin concentration, erythrocyte and leukocyte counts, packed cell volume; and throbocytes. Glucose (fasting overnight) was examined in whole blood samples at week 27, 52, 78, and 104.
- Clinical Chemisty
Blood samples of 10 rats per dose per sex collected at week 28, 53, 79, and 105 were analysed for alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, total protein, albumin, total bilirubin, urea, creatinine, cholesterol, gamma-glutamyl transferase, inorganic phosphate, calcium, chloride, sodium, potassium.
- Urinalysis
In week 27, 52, 78, 104 rats (10 rats per dose per sex) were deprived of water for 24 h and last 16 h urine collected. Urine volume and density determined. In pooled urine samples collected at week 27 and 104 semi-quantitative observations of protein, glucose, occult blood, ketones, urobillinogen and billirubin were made. Sediment was examined via light microscopy.
Sacrifice and pathology:
Survivors of two subgroups (each 10 rats per dose per sex) were killed at week 53 and at week 79. Survivors of 50 rats per dose per sex were killed at week 105.
- Organ Weights
Determined of adrenals, brain, liver, heart, kidneys, spleen, testes, pituitary, thyroid, ovaries.

- Gross pathology
Necropsy of rats in all 4 main and sub-groups performed after sacrifice.

- Histopathology
All organs listed in OECD453 were examined in control and high dose groups. Liver, lungs, stomach and nose were examined also in low and mid dose groups. Furthermore, adrenals, kidney, spleen, testes, thyroid, ovaries, pituitary and mammary gland of rats killed at week 105 of low and mid dose group were examined.
Tissues of rats that were found dead or killed moribund were also preserved if autolysis was not advanced.
Other examinations:
no
Statistics:
Suitable statistical methods were used (one-way analysis of covariance; Dunnett's test; Mann-Whitney U-test and Fishers exact test), the level of significance was p=0.05.
Clinical signs:
effects observed, non-treatment-related
Description (incidence and severity):
5 mg/kg bw: No treatment related effects were observed.
25 & 125 mg/kg bw: fur with yellowish discoloration from week 3 onwards, more pronounced in the high dose group. This discoloration is due to formaldehyde spilt on the fur from drinking bottles.
Mortality:
mortality observed, non-treatment-related
Description (incidence):
There was no toxicologically significant difference in mortality between treatment groups and controls.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
5 & 25 mg/kg bw: No effects
125 mg/kg bw: in males significant decrease from week 1 onwards and in females from week 24 onwards.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
5 & 25 mg/kg bw: no effects
125 mg/kg bw: In males (in females less pronounce) significantly decreased food intake.
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
effects observed, treatment-related
Description (incidence and severity):
5 & 25 mg/kg bw: no effects
125 mg/kg bw: In males & females water consumption significantly decreased (ca. 40% reduction).
Ophthalmological findings:
not examined
Haematological findings:
no effects observed
Description (incidence and severity):
No effects in any treatment group.
Clinical biochemistry findings:
effects observed, non-treatment-related
Description (incidence and severity):
At week 27 and 79 slight (no details given on statistical significance) changes were seen in clinical chemistry of mid and high dose rats. But no significant effects were noted at week 53 and 105. Therefore, these effects were not considered to be of toxicological relevance.
Urinalysis findings:
effects observed, treatment-related
Description (incidence and severity):
A significant increase in urine density and decreased volume in the high dose group in m&f at week 27 and in m at week 52 was reported. These effects were due to reduced water intake.
Mean urinary pH was increased in m at 5 and 25 mg/kg bw in week 27 and 78 and was decreased in females at 125 mg/kg bw in week 27, 52, and 78. Occult blood was increased in males of all treatment groups at week 27 and in females at 25 and 125 mg/kg bw in week 104. A clear dose-effect relationship was not given suggesting no toxicological significance.
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
5 & 25 mg/kg bw: no effects
125 mg/kg bw: relative brain weight was increased in m & f, rel. testis weight increased in males and relative kidney weight increased in females. These increases are considered to be a result of decreased body weight.
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
Treatment related changes were detected only in the stomach. The limiting ridge of the forestomach was thickened and irregular mucosal thickenings in the forestomach and/or the glandular stomach. Of high dose males and females. Occasional these alterations were also seen in other groups including controls.
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
No effects were detected except lesions of the forestomach and glandular stomach (see Table) and renal changes in week 105 in high dose groups.
Lesions of the forestomach and glandular stomach:
a) Focal papillary epithelial hyperplasia and focal hyperkeratosis in the forestomach
b) chronic atrophic gastritis, focal ulcerations and glandular hyperplasia in the glandular stomach

Renal changes:
The incidence and degree of renal papillary necrosis was significantly increased in males and females in week 105 (not in week 53 and 79). These changes were located at the tip of the papilla and were characterized by patchy necrosis of interstitial cells, capillaries and loops of Henle.
Histopathological findings: neoplastic:
effects observed, non-treatment-related
Description (incidence and severity):
There was no treatment related increase in any tumour type. In contrast, the total number of tumours and the number of tumour-bearing rats was lower in high dose males compared to controls.
Relevance of carcinogenic effects / potential:
Hyperplasia in forestomach and glandular stomach but no tumour formation after chronic exposure in rats via the drinking water.
Dose descriptor:
NOAEL
Effect level:
82 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: highest dose level tested (concentration 0.19%)
Remarks on result:
other: Effect type: carcinogenicity
Dose descriptor:
NOAEL
Effect level:
109 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
female
Basis for effect level:
other: highest dose level tested (concentration 0.19%)
Remarks on result:
other: Effect type: carcinogenicity
Dose descriptor:
NOAEL
Effect level:
15 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: concentration in drinking water: 0.026%
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
NOAEL
Effect level:
21 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
female
Basis for effect level:
other: concentration in drinking water: 0.026%
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
LOAEL
Effect level:
82 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: local effects in the stomach; concentration in drinking water: 0.19%
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
LOAEL
Effect level:
109 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
female
Basis for effect level:
other: local effects in the stomach; concentration in drinking water: 0.19%
Remarks on result:
other: Effect type: toxicity

 

Incidence of hyperplasia and other lesions in the forestomach and glandular stomach of rats after chronic exposure via the drinking water

Type of lesion

Males, dose in mg/kg bw

Females, dose in mg/kg bw

0

5

25

125

0

5

25

125

Week 53

Number of rats examined

9

10

10

10

10

10

10

9

Forestomach

Focal papillary epithelial hyperplasia

0

0

0

7

0

0

0

5

Glandular stomach

Chronic atrophic gastritis

0

0

0

10***

0

0

0

9***

Focal ulceration

0

0

0

3

0

0

0

1

Week 79

Number of rats examined

10

10

10

10

10

9

10

9

Forestomach

Focal papillary epithelial hyperplasia

2

1

1

8

1

0

1

9

Glandular stomach

Chronic atrophic gastritis

0

0

0

10***

0

0

0

10***

Focal ulceration

0

0

0

2

0

0

0

0

Week 105

Number of rats examined

47

45

44

47

48

49

47

48

Forestomach

Focal papillary epithelial hyperplasia

1

2

1

45***

1

0

2

45***

Focal hyperkeratosis

2

6

4

24***

3

5

3

33***

Focal ulceration

1

1

1

8

0

0

2

5

Glandular stomach

Chronic atrophic gastritis

0

0

0

46***

0

0

0

48***

Focal ulceration

0

0

0

11***

0

0

0

10***

Glandular hyperplasia

0

1

0

20***

0

0

0

13***

***: p<0.001

 

Conclusions:
Oral exposure via the drinking water induced non-neoplastic local effects in the stomach of rats at a concentration of 0.19% corresponding to 82 mg/kg bw/d in males and 109 mg/kg bw/d in females; the NOAEC is 0.026% corresponding to 15 mg/kg bw/d in males and 21 mg/kg bw/d in females.
Executive summary:

In a combined chronic toxicity/carcinogenicity study (all parameters tested as recommended in OECD 453) 70 male and 70 female Wistar rats per dose (subgroups of 10 rats/sex/dose killed 12 or 18 months after start of exposure) received via the drinking water 0, 1.2, 15, 82 mg/kg bw/day (males) or 0, 1.8, 21, 109 mg/kg bw/day (females) for 105 weeks (concentration: 0, 20, 260, or 1900 mg/L or 0, 0.002, 0.026, 0.19%). At the high dose body weight gain was decreased in males & females and food and water consumption decreased. Other parameters (except pathology) were not altered. Pathological alterations in the kidney like the renal papillary necrosis detected in high dose males and females is discussed as an effect of the reduced water intake and is indirectly treatment related. Treatment related lesions were detected in the forestomach (focal papillary epithelial hyperplasia, ulceration and hyperkeratosis) and the glandular stomach (chronic atrophic gastritis, ulceration and hyperplasia) of males and females in the high dose group. No gastric tumours were induced. This study did not provide any evidence of carcinogenicity in rats after oral administration of formaldehyde.

Conclusion: Oral exposure via the drinking water induced non-neoplastic local effects in the stomach of rats at a concentration of 0.19% corresponding to 82 mg/kg bw/d in males and 109 mg/kg bw/d in females; the NOAEC is 0.026% corresponding to 15 mg/kg bw/d in males and 21 mg/kg bw/d in females.

Carcinogenicity: via inhalation route

Link to relevant study records

Referenceopen allclose all

Endpoint:
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Comparable to OECD guideline 453 with acceptable restrictions (adrenal weights not measured, no histopathology of sternum, larynx and pharynx).
Reason / purpose:
reference to same study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
Deviations:
no
GLP compliance:
no
Specific details on test material used for the study:
- Specification: Thermal depolymerisation of paraformaldehyde
- Source: Aldrich Chemicals, Milwaukee, WI, USA
- Batch no.: 041967 and TA 113067
- purity checked by GC-MS after generation of formaldehyde gas and emission spectroscopy of praformaldehyde (no metallic impurities)
Species:
mouse
Strain:
B6C3F1
Sex:
male/female
Details on test animals and environmental conditions:
- Source Charles River, Portage, MI, USA
- Age/weight at study initiation: 6 weeks / no data
- Acclimatization: 1 week after arrival
- randomization
- Housing conditions:
4 mice of the same sex per cages; certified diet and water ad libitum (not during exposure), 12 h light/dark cycle, 15 fresh air changes per hour; temperature of 70°F + 2, a relative air humidity of 45 +- 5%
Route of administration:
inhalation: gas
Type of inhalation exposure (if applicable):
whole body
Vehicle:
air
Details on exposure:
Temperature 20-22°C and rel. air humidity 51-61%. Gas was generated by thermal depolymerisation of paraformaldehyde and mixed with cleaned air before introduction into the 5 m³ exposure chamber.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Concentration monitored by the IR spectrophotometer at least once per hour.
Duration of treatment / exposure:
Exposure period 24 months
Frequency of treatment:
6 h/day for 5 days per week
Post exposure period:
3 months in females
Dose / conc.:
2 ppm (nominal)
Remarks:
- 2.4 mg/m³ (nominal)
- 2.0 ± 0.01 ppm (mean ± SE); (analytical)
- 2.0 ± 0.6 ppm (mean ± SD; CIIT 1981) (analytical)
Dose / conc.:
6 ppm (nominal)
Remarks:
- 7.2 mg/m³ (nominal)
- 5.6 ± 0.02 ppm (mean ± SE); (analytical)
- 5.6 ± 1.2 ppm (mean ± SD; CIIT 1981) (analytical)
Dose / conc.:
15 ppm (nominal)
Remarks:
- 19 mg/m³ (nominal)
- 14.3 ± 0.04 ppm (mean ± SE); (analytical)
- 14.3± 2.8 ppm (mean ± SD; CIIT 1981) (analytical)
No. of animals per sex per dose:
Number of animals per group: 119-121 per dose per sex (interim sacrifice(s))
Control animals:
yes, sham-exposed
Details on study design:
- Interim sacrifice(s)
Interim sacrifices were conducted at 6, 12, 18, 24, and 27 (only females) months (9-41 mice per dose per sex; no survival > 24 months in males)
- Final sacrifice after 27 months (post-exposure period up to 3 months) in females and after 24 months in males (increased unscheduled deaths)
- group size on interim sacrifice: 10 mice per sex per dose at 6 and 12 months, 20 females/dose at 18 months (no males), 17-41 mice/sex/dose at 24 months, and 9-16 females/dose at 27 months
Positive control:
no
Observations and examinations performed and frequency:
- Body weight: Yes, weekly the 1st 6 months, thereafter biweekly.
- Food consumption: No data
- Water consumption: No data
- Clinical signs: Checked twice daily
- Makroskopic investigations: No data
- Ophthalmoscopic examination: Yes, prior to exposure and before sacrifice; iris, lens, cornea, fundus and conjunctiva examined

- Haematology: Yes
Number of animals: 10 animals/sex/group
Time points: 6, 12, 18, 24, 27, 30 months after start of experiment. (see interim sacrifice)
Parameters: hemoglobin (HGB), hemarocrit (HCT), white blood count (WBC), red blood count (RBC), mean cell volume (MCV), mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), reticulocytes, and a differential white cell count

- Clinical Chemistry: Yes
Number of animals: 10 animals/sex/group
Time points: 6, 12, 18, 24, 27, 30 months after start of experiment. (see interim sacrifice)
Parameters: glucose, blood urea-nitrogen (BUN), alkaline phosphatase (AP), serurm glutamic-oxaloacetic transaminase (SGOT), and serum glutamic-pyruvic transaminase (SGPT); creatine phosphokinase (only 6 months sacrifice)

- Urinalysis: Yes
Number of animals: 10 animals/sex/group (same animals used for haematology and clinical chemistry), 16-h urine in metabolism cages collected.
Time points: 6, 12, 18, 24, 27, 30 months after start of experiment. (see interim sacrifice)
Parameters: total volume (Vol), specific gravity (Sp. Gr.), pH, glucose (Glu), ketones, protein (Prot), occult blood (Occ), and urine sediment.

- Neurofunctional study: prior to scheduled sacrifice starting after 18 months of exposure; parameters: posture and gait, facial tone, pupil reflex, palpebral reflex, extensor reflex, clutch response
Sacrifice and pathology:
- Pathology
Yes, necropsy performed on all animals that died or were sacrificed at the scheduled intervals.
- Organ Weights: heart, brain, gonads. liver, kidneys, and lungs measured
- Histopathology
Yes, from nasal cavity, all dose groups; 3 cross section levels
Major tissues of high dose group and controls
Organs: all organs recommended in OECD Guideline 453 examined histopathologically, exceptions see reliability
Other examinations:
Other examinations: reversibility of effects
Statistics:
Suitable methods used:
Bartlett's test, ANOVA, Kruskal-Wallis test, Dunnett's test, Dunn test, chi-square test for homogeneity, life Table method, Fisher exact test.
Level of significance: p< 0.05.
Clinical signs:
effects observed, non-treatment-related
Description (incidence and severity):
observed signs were sporadic and inconsistent and contribute litte information that is useful in the evaluation of formaldehyde
Mortality:
mortality observed, non-treatment-related
Description (incidence):
Mortality rate was not increased in male and female mice in comparison to control. In male mice (including controls) a generally poor survival was due to fighting (4 males in one cage) and infections of the genitourinary tract (not treatment related). 41, 33, 32, and 25 male mice survived a minimum of 18 months at 0, 2, 6, 15 ppm, respectively.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
At 15 ppm there was a significant trend towards lower body weight at >= week 72 in females, but this effect was reversible in the post exposure observation period. The rate of growth through the first 8 weeks tor male mice at the 15-ppm exposure level was significantly less than control and was interpreted as a treatment-related effect.
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
effects observed, non-treatment-related
Description (incidence and severity):
Ophthalmology revealed no treatment related effects.
Haematological findings:
effects observed, non-treatment-related
Description (incidence and severity):
scattered findings of statistically significant effects but considered to be not treatment related (no trend, no dose response relationship)
Clinical biochemistry findings:
effects observed, non-treatment-related
Description (incidence and severity):
scattered findings of statistically significant effects but considered to be not treatment related (no trend, no dose response relationship)
Urinalysis findings:
no effects observed
Description (incidence and severity):
data were within normal limits
Behaviour (functional findings):
effects observed, non-treatment-related
Description (incidence and severity):
Neurofunctional study revealed no treatment related effects.
Organ weight findings including organ / body weight ratios:
effects observed, non-treatment-related
Description (incidence and severity):
no significant effects on absolute and relative organ weights in males. Changes in the female mice were often inconsistent across exposure groups and their biological significance was questionable due to the lack of pathologic correlates and the lack of supporting clinical chemistry. Examples: in females rel weights at 2 ppm/ 12 months were increased for heart, brain, right and left kidneys, and lung (due to altered body weight); rel (but not absolute) heart weight increased (15 ppm, 12 months), ovary increased (6 ppm, 6 months), liver decreased (15 ppm, 6 months), left, but not right, kidney decreased (15 ppm, 6 months; 6 ppm, 18 months). Conclusion: incidental and not treatment related.
Gross pathological findings:
not specified
Description (incidence and severity):
no data reported
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Treatment related effects were detected only in the nasal cavity (see Table). No effects were noted in the trachea (compare with data on rats).

2 ppm: no effects were noted in the nasal cavity except rhinitis in a few animals after 24 months (also found in controls, unscheduled deaths, considered to be not treatment related). Epithelial dysplasia of the nasal epithelium was found at the low dose level and not detected in controls. This effects might be of toxicological relevance (not discussed by the authors) but the incidence was were low (3/120 males and 1/120 females). No effects detected in treated female mice after 27 months (3 months post exposure observation period).

6 ppm: 1st effects were detected at month 18, a few mice (no data on significance) had dysplastic changes associated with severe rhinitis in the more anterior part of the nasal cavity (respiratory epithelium). At month 24 additionally metaplasia was observed and focal atrophy of the olfactory epithelium (but “reduced frequency” compared with the high dose group, presumably not significant). Female mice were free of test substance related lesions at month 27 (terminal sacrifice of a small sub-group). Statistical significance was reached for epithelial dysplasie in the nasal cavity of males and females and squamous metaplasia in the nasal cavity of males.

15 ppm: 1st effects were detected at month 12. Mice exhibited serous rhinitis in more posterior part of the nasal cavity. Dysplastic and metaplastic alterations of the nasal mucosa were reported at month 18, associated with purulent exudate (rhinitis). At month 24 (interim sacrifice) most (>90%) of mice had dysplastic and metaplastic changes associated with seropurulent rhinitis; hyperplasia of the squamous epithelium lining the nasolacrimal duct as well as focal atrophy of the olfactory epithelium occurred.

Statistical significance was reached for epithelial dysplasia and metaplasia in the nasal cavity, epithelial hyperplasia in the nasolacrimal duct, rhinitis, and atrophy of the olfactory epithelium of males and females.
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
15 ppm: At month 24 (interim sacrifice) most (>90%) of mice had dysplastic and metaplastic changes associated with seropurulent rhinitis; hyperplasia of the squamous epithelium lining the nasolacrimal duct as well as focal atrophy of the olfactory epithelium occurred. At this time point 2 males had squamous cell carcinomas in the nasal cavity originating from epithelium of nasoturbinates. Location and morphology were similar to those observed in rats.
Relevance of carcinogenic effects / potential:
Ambiguous test results concerning carcinogenic effects, low incidence of squamous cell carcinoma in the nasal cavity of males at the high dose (not significant but presumably of toxicological relevance).
Dose descriptor:
NOAEC
Effect level:
2 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: lowest dose tested
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
LOAEC
Effect level:
6 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: local effects in the nasal cavity like epithelial dysplasia and metaplasia
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
NOAEC
Effect level:
15 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: highest dose level tested; NOAEC for males questionable since 2 males had squamous cell carcinomas in the nasal cavity (statistically not significant but presumably of toxicological relevance)
Remarks on result:
other: Effect type: carcinogenicity
Non-neoplastic effects including hyperplasia in the nasal cavity of mice exposed for up to 24 months including interim sacrifice of sub-groups and mice found dead/moribund

Dose level in ppm (nominal)

0

2

6

15

Sex

Males

Females

Males

Females

Males

Females

Males

Females

Total number of animals

119

121

120

120

120

120

119

121

Incidences of lesions

Epithelial dysplasia

0

0

3

1

34

14

34

87

Squamous metaplasia of epithelium

0

0

1

0

17

6

34

59

Squamous epithelial hyperplasia of the nasolacrimal duct

3

0

0

4

0

1

12

18

Atrophy of olfactory epithelium

1

2

1

0

1

3

11

13

Data on rhinitis were not given in the Summary Table and not readable in other Tables in CIIT (1981; insufficient documentation in Kerns et al., 1983); no data about statistical significance but clear effects at the mid and high dose level; it is not clearly stated that all animals necropsied are included in the number of animals evaluated for the specific organ.

Conclusions:
Chronic formaldehyde inhalation induced local effects in the nasal cavity of mice; the effects are less severe than in rats. NOAEC is 2 ppm and the LOAEC 6 ppm.
Executive summary:

Study is comparable to OECD guideline 453 with acceptable restrictions (adrenal weights not measured, no histopathology of sternum, larynx and pharynx).

Inhalation exposure of male and female B6C3F1 mice for 2 years at dose levels of 0, 2, 6, 15 ppm (120 mice per sex per dose; 24 months exposure, 6 h per day, 5 days per week; post exposure period 3 months [only female]; interim sacrifices) resulted only in local effects in the nasal cavity of males and females, predominantly in the respiratory epithelium. Rhinitis, dysplasia, squamous metaplasia were induced, but also atrophy of olfactory epithelium with increasing exposure periods at the high dose level. Except reduced body weight no further effects were detected. The NOAEC was 2 ppm and the LOAEC 6 ppm. In contrast to rats only a few tumours were detected in the nasal cavity at 15 ppm [However, in males the high mortality rate (not treatment related but due to housing conditions) might influence the outcome of this study]. Generally the lesions in mice were less severe than in rats (see also CIIT 1981 & Kerns et al. 1983 in Section 7.5.3 & 7.7).

Conclusion: Chronic formaldehyde inhalation induced local effects in the nasal cavity of mice; the effects are less severe than in rats. TheNOAEC is 2 ppm and the LOAEC 6 ppm. Ambiguous test results were obtained concerning carcinogenic effects, the low incidence of squamous cell carcinoma in the nasal cavity of males at the high dose was not significant but presumably of toxicological relevance.

Endpoint:
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Comparable to OECD guideline 453 with acceptable restrictions (no histopathology of sternum, larynx and pharynx).
Reason / purpose:
reference to same study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
Deviations:
no
GLP compliance:
no
Specific details on test material used for the study:
- Specification: Thermal depolymerisation of paraformaldehyde
- Source: Aldrich Chemicals, Milwaukee, WI, USA
- Batch no.: 041967 and TA 113067
- purity checked by GC-MS after generation of formaldehyde gas and emission spectroscopy of praformaldehyde (no metallic impurities)
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
- Age/weight at study initiation: 6 weeks / no data
- Source Charles River, Portage, MI, USA
- Age/weight at study initiation: 6 weeks / no data
- Acclimatization: 1 week after arrival
- randomization
- Housing conditions:
4 mice of the same sex per cages; certified diet and water ad libitum (not during exposure), 12 h light/dark cycle, 15 fresh air changes per hour; temperature of 70°F + 2, a relative air humidity of 45 +- 5%
Route of administration:
inhalation: gas
Type of inhalation exposure (if applicable):
whole body
Vehicle:
other: air
Details on exposure:
Temperature 20-22°C and rel. air humidity 51-61%. Gas was generated by thermal depolymerisation of paraformaldehyde and mixed with air (no details) before introduction into the 5 m³ exposure chamber.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Concentration monitored by the IR spectrophotometer at least once per hour.
Duration of treatment / exposure:
Exposure period 24 months
Frequency of treatment:
6 h/day for 5 days per week
Post exposure period:
Up to 6 months
Dose / conc.:
2 ppm (nominal)
Remarks:
- 2.4 mg/m³
- 2.0 ± 0.01 ppm (mean ± SE); (analytical)
- 2.0 ± 0.6 ppm (mean ± SD; CIIT 1981) (analytical)
Dose / conc.:
6 ppm (nominal)
Remarks:
- 2.4 mg/m³
- 5.6 ± 0.02 ppm (mean ± SE); (analytical)
- 5.6 ± 1.2 (mean ± SD; CIIT 1981); (analytical)
Dose / conc.:
15 ppm (nominal)
Remarks:
- 19 mg/m³
- 14.3 ± 0.04 ppm (mean ± SE); (analytical)
- 14.3 ± 2.8 ppm (mean ± SD; mg/m³); (analytical)

; CIIT 1981
No. of animals per sex per dose:
Number of animals per group: 119-121 per dose per sex (interim sacrifices)
Control animals:
yes, sham-exposed
Details on study design:
Interim sacrifices were conducted at 6, 12, 18, 24, 27, 30 months
- post exposure period 3 (sacrifice at 27 months) or 6 months (sacrifice at 30 months) for sub-groups
- details for interim sacrifice: 10 rats/sex/dose at 6 and 12 months; 19-20 rats at 18 months; 41-54 rats/sex/dose at dose levels of 0, 2, or 6 ppm but only 13-14 rats/sex at the high dose level (due to toxicity and increased unscheduled sacrifice) after 24 months of exposure; at 27 months 9-10 rats (but at high dose level only 5 males, no females) per sex per dose; at 30 months only 1-6 rats/sex/dose (no rats of the high dose group).
Positive control:
no
Observations and examinations performed and frequency:
- Body weight: Yes, weekly the 1st 6 months, thereafter biweekly.
- Food consumption: No data
- Water consumption: No data
- Clinical signs: Checked twice daily
- Makroskopic investigations at necropsy: No data
- Ophthalmoscopic examination: Yes, prior to exposure and before sacrifice; iris, lens, cornea, fundus and conjunctiva examined

- Haematology: Yes
Number of animals: 10 animals/sex/group
Time points: 6, 12, 18, 24, 27, 30 months after start of experiment. (see interim sacrifice)
Parameters: hemoglobin (HGB), hemarocrit (HCT), white blood count (WBC), red blood count (RBC), mean cell volume (MCV), mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), reticulocytes, and a differential white cell count

- Clinical Chemistry: Yes
Number of animals: 10 animals/sex/group
Time points: 6, 12, 18, 24, 27, 30 months after start of experiment. (see interim sacrifice)
Parameters: glucose, blood urea-nitrogen (BUN), alkaline phosphatase (AP), serurm glutamic-oxaloacetic transaminase (SGOT), and serum glutamic-pyruvic transaminase (SGPT); creatine phosphokinase (only 6 months sacrifice)

- Urinalysis: Yes
Number of animals: 10 animals/sex/group (same animals used for haematology and clinical chemistry), 16-h urine in metabolism cages collected.
Time points: 6, 12, 18, 24, 27, 30 months after start of experiment. (see interim sacrifice)
Parameters: total volume (Vol), specific gravity (Sp. Gr.), pH, glucose (Glu), ketones, protein (Prot), occult blood (Occ), and urine sediment.

- Neurofunctional study: prior to scheduled sacrifice starting after 18 months of exposure; parameters: posture and gait, facial tone, pupil reflex, palpebral reflex, extensor reflex, clutch response
Sacrifice and pathology:
- Pathology
Yes, necropsy performed on all animals that died or were sacrificed at the scheduled intervals.
- Organ Weights: heart, brain, gonads. liver, kidneys, adrenals and lungs measured
- Histopathology
Yes, from nasal cavity, all dose groups; 5 cross section levels
Major tissues of high dose group and controls, additionally low and mid dose if effects were recorded
Organs: all organs recommended in OECD Guideline 453 examined histopathologically, exceptions see reliability
Other examinations:
reversibility of effects
Statistics:
Suitable methods used:
Bartlett's test, ANOVA, Kruskal-Wallis test, Dunnett's test, Dunn test, chi-square test for homogeneity, life Table method, Fisher exact test.
Level of significance: p< 0.05.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
Concentration dependent yellow discoloration of the fur (no adverse effect); reversible effect.
15 ppm: rats dyspneic & emaciated and many rats with facial swelling due to tumour nasal formation.
Mortality:
mortality observed, treatment-related
Description (incidence):
Mortality was dose dependently increased, significant at 6 ppm (p<0.05) and 15 ppm (p<0.001).
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Significantly (p<0.05) reduced body weight at 6 and 15 ppm in males and females. Slight but not significant effects at 2 ppm.
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
effects observed, non-treatment-related
Description (incidence and severity):
Ophthalmology revealed no treatment related effects.
Haematological findings:
effects observed, non-treatment-related
Description (incidence and severity):
scattered findings of statistically significant effects but considered to be not treatment related (no trend, no dose response relationship)
Clinical biochemistry findings:
effects observed, non-treatment-related
Description (incidence and severity):
scattered findings of statistically significant effects but considered to be not treatment related (no trend, no dose response relationship)
Urinalysis findings:
no effects observed
Description (incidence and severity):
data were within normal limits
Behaviour (functional findings):
effects observed, non-treatment-related
Description (incidence and severity):
Neurofunctional study revealed no treatment related effects.
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
Changes in the females and males were often inconsistent across exposure groups and their biological significance was questionable due to the lack of pathologic correlates and the lack of supporting clinical chemistry. The absolute weight decreases in liver and kidney might be the result of formaldehyde exposure of the 15-ppm male rats, however, other parameters were negative (clin. chemistry, histopathology).
Gross pathological findings:
not specified
Description (incidence and severity):
no data
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Effects were detected only in nasal cavity and proximal trachea.

2 ppm: purulent rhinitis, epithelial dysplasia, and squamous metaplasia were present in the anterior part of the nasal cavity, all effects were significantly increased compared with control at >= 2ppm. Dysplasia occurred earlier than metaplasia. In males & females (not at 6 ppm) significantly increased goblet cell hyperplasia was detected at >= 2 ppm.

6 ppm: purulent rhinitis, epithelial dysplasia, and squamous metaplasia were noted also in more posterior parts of the nasal cavity (compare with 2 ppm) but with an anterior-posterior gradient for severity. A regression of lesions was observed at month 27 (post exposure observation period).

15 ppm: squamous metaplasia with squamous hyperplasia and increased keratinisation was seen as well as significant atrophy of the olfactory epithelium including metaplasia of this epithelium.

Non-neoplastic lesions of the proximal trachea were noted in the high dose group (18 and 24 month sacrifice but not after 27 and 30 months): epithelial dysplasia (significant in males and females), squamous metaplasia (significant in females).
In bone marrow the incidence in hyperplasia was significantly increased in males (26/120 versus 8/120 in control) and females (28/120 versus 7/120 in control) (not discussed by the authors), a secondary effect is not excluded.
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
2 ppm: Tumour formation: Polypoid adenomas were reported in the nasal mucosa but the incidence was not significant (also detected in one control rat).

6 ppm: Polypoid adenomas were noted in nasal mucosa but the incidence was not significant (also detected in one control rat, no dose dependency in females, see Table below). 1 male and 1 female rat developed a squamous cell carcinoma (not significant).

15 ppm: a sharp increase in squamous cell carcinoma was reported (51/120 males and 52/120 females), tumours invaded other tissues including bone. Predominant localisation of tumours: anterior portion of the lateral side of the nasal turbinate and the adjacent lateral wall or the midventral septum.
Relevance of carcinogenic effects / potential:
Clearly carcinogenic effects in the nasal cavity of rats were reported after 2 years inhalation at a dose level of 15 ppm formaldehyde.
Dose descriptor:
LOAEC
Effect level:
2 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: lowest dose level tested; local effects in the nasal cavity (purulent rhinitis, epithelial dysplasia, and squamous metaplasia)
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
LOAEC
Effect level:
15 ppm (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: squamous cell carcinomas of the nasal cavity
Remarks on result:
other: Effect type: carcinogenicity
Dose descriptor:
NOAEC
Effect level:
6 ppm (nominal)
Sex:
male/female
Basis for effect level:
other: questionable NOAEC, incidence of squamous cell carcinoma not of statistical significance but possibly of toxicological relevance
Remarks on result:
other: Effect type: carcinogenicity

Neoplastic and non-neoplastic effects in the nasal cavity of rats exposed for up to 24 months including interim sacrifice of sub-groups and rats found dead/moribund

Dose level in ppm (nominal)

0

2

6

15

Sex

Males

Females

Males

Females

Males

Females

Males

Females

Total number of animals

120

120

120

120

120

120

120

120

Incidences of lesions

Epithelial dysplasia

3

1

25

43

71

54

31

21

Goblet cell hyperplasia

3

8

27

38

19

12

5

4

Atrophy of olfactory epithelium

0

1

0

0

0

0

8

5

Olfactory epithelial metaplasia goblet/ciliated cells

0

1

0

0

1

1

8

8

Olfactory epithelial squamous metaplasia

0

0

0

0

0

0

9

10

Squamous atypia

0

0

0

0

1

0

11

11

Squamous cell carcinoma

0

0

0

0

1

1

51

52

Squamous epithelium hyperplasia

3

6

1

0

6

7

23

39

Squamous epithelium papillary hyperplasia

0

0

0

0

0

0

10

12

Squamous metaplasia

5

5

55

49

67

70

78

79

Data on rhinitis were not given in the Summary Table and not readable in other Tables in CIIT (1981; insufficient documentation of these data in Kerns et al., 1983); no data about significance; it is not clearly stated that all animals necropsied are included in the number of animals evaluated for the specific organ.

Conclusions:
Non-neoplastic local effects in the nasal cavity of rats were found even at the low dose level of 2 ppm in a long-term inhalation study in rats; tumours in the nasal cavity at a dose level of 15 ppm.
Executive summary:

Study is comparable to OECD guideline 453 with acceptable restrictions (no histopathology of sternum, larynx and pharynx).

Inhalation exposure of male and female F344 rats for 2 years at dose levels of 0, 2, 6, 15 ppm (120 rats per sex per dose; 24 months exposure, 6 h per day, 5 days per week; post exposure period 6 months; interim sacrifices) resulted exclusively in local effects of the nasal cavity and of the proximal trachea in males and females. Only non-neoplastic effects were reported in the high dose group in the proximal trachea but a high incidence in squamous cell carcinomas of the nasal cavity (51/120 males and 52/120 females). Carcinogenic effects in the mid dose group (squamous cell carcinomas in nasal cavity of 1 male and 1 female) are not of statistical significance but possibly of toxicological relevance. At 2 ppm purulent rhinitis, epithelial dysplasia, and squamous metaplasia were present in the anterior part of the nasal cavity. Dysplasia occurred earlier than metaplasia. Non-neoplastic effects in the mid dose group like dysplasia and squamous cell metaplasia in the nasal cavity occurred also in more posterior parts or the nasal cavity.

Conclusion: Non-neoplastic local effects in the nasal cavity of rats were reported even at the low dose level of 2 ppm in a long-term inhalation study in rats; tumours in the nasal cavity were found at a dose level of 15 ppm.

Endpoint:
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
The study meets generally accepted scientific standards with acceptable restrictions concerning local effects: Partly no data or only limited documentation (e.g. test substance, control). Only males tested; restricted to local effects; no data on sacrifice of moribund animals (possible autolysis of tissues in hamsters found dead); Methods in experiment B-E insufficient (only dissecting microscope used). Not valid for experiments B-E (reliability 3)
Principles of method if other than guideline:
Carcinogenicity study of formaldehyde in Syrian golden hamster exposed for lifetime via inhalation
GLP compliance:
not specified
Specific details on test material used for the study:
Thermal depolymerisation of paraformaldehyde, no further data
Species:
hamster, Syrian
Strain:
other: Syrian golden hamster
Sex:
male
Details on test animals and environmental conditions:
No details
Route of administration:
inhalation: gas
Type of inhalation exposure (if applicable):
whole body
Vehicle:
air
Details on exposure:
No data on temperature and rel. air humidity. Gas was generated by thermal depolymerisation of paraformaldehyde and mixed with air (no details) before introduction into the 1.5 m³ exposure chamber.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Concentration monitored routinely by the colorimetric analysis of dissolved formaldehyde in water through which chamber air has been bubbled.
Duration of treatment / exposure:
Lifetime
Frequency of treatment:
5 h per day, see also details of study design
Post exposure period:
No
Dose / conc.:
10 ppm (nominal)
Remarks:
concentration within 5% of desired levels
Dose / conc.:
30 ppm (nominal)
Remarks:
concentration within 5% of desired levels
No. of animals per sex per dose:
A) 0 or 10 ppm, 5 h/day, 5 days/week for lifetime: 132 controls and 88 treated hamster
B) 0 or 30 ppm, 5 h/day, once per week for lifetime: 50 hamster per group
C) Diethylnitrosamine (DEN) alone (s.c. 0.5 mg/hamster, once per week for 10 weeks): 100 hamsters
D) 2 days prior to each DEN treatment animals exposed to 30 ppm formaldehyde (5 h/day); thereafter 5 h/day, once per week for lifetime: 50 animals
E) 2 weeks after DEN treatment for 10 weeks animals exposed to 30 ppm formaldehyde for lifetime: 50 animals
Control animals:
other: Yes, but presumably not sham exposed (limited documentation)
Details on study design:
A) 0 or 10 ppm, 5 h/day, 5 days/week for lifetime
B) 0 or 30 ppm, 5 h/day, once per week for lifetime
C) Diethylnitrosamine (DEN) alone (s.c. 0.5 mg/hamster, once per week for 10 weeks)
D) 2 days prior to each DEN treatment animals exposed to 30 ppm formaldehyde (5 h/day); thereafter 5 h/day, once per week for lifetime
E) 2 weeks after DEN treatment for 10 weeks animals exposed to 30 ppm formaldehyde for lifetime
Positive control:
DEN
Observations and examinations performed and frequency:
Body weight: No data
Food consumption: No data
Water consumption: No data
Clinical signs: No data
Makroskopic investigations: No data
Ophthalmoscopic examination: No data
Haematology: No data
Clinical Chemistry: No data
Urinalysis: No data
Sacrifice and pathology:
- Pathology
Yes, necropsy performed on all animals but no data given in the result section
- Organ Weights: No data
- Histopathology
Exp. A
2 transverse sections of the nasal turbinates, longitudinal sections of larynx and trachea, and all lung lobes along the bronchus were examined.
Exp. B-D
no light microscopy of paraffin sections but examination of the same tissues than in A by a dissecting microscope after clearing and staining of tissue. Lesions < 1mm not counted as tumour. Only 10 lesions in each tissue of each treatment group examined via standard light microscopical methods.
Study directed to effects in the respiratory tract.
Other examinations:
no
Statistics:
Suitable methods used; level of significance: p<= 0.05.
Clinical signs:
effects observed, treatment-related
Mortality:
mortality observed, treatment-related
Description (incidence):
A) Significantly reduced survival time in the treatment group (p<0.05).
B) No effects. C) Significantly increased. In D and E further increase in mortality rate but low number of animals due to an exposure accident (n= 27 and 23 hamsters evaluated in D and E, respectively).
Body weight and weight changes:
not specified
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not specified
Haematological findings:
not specified
Clinical biochemistry findings:
not specified
Urinalysis findings:
not specified
Behaviour (functional findings):
not specified
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
A) 10 ppm induced metaplasia and hyperplasia (no further details) in the nasal epithelium of 5% of the treated hamster (no further data on incidence but presumably 4/88) but none in controls. Incidence of rhinitis not influenced.

Histopathological findings: neoplastic:
no effects observed
Description (incidence and severity):
A) No tumour formation.
In C) 77% of animals with a tumour at one or more sites of the respiratory tract; all tumours were adenomas. No effect on tumour incidence has been detected in D) and E). A significant increase in number of tumours per tumour bearing animals was noted in D); however, the validity of this result is restricted (low number of animals due to the exposure accident; method for evaluation of tumours in the respiratory tract is limited).
In B) no tumours detected in any control or treated hamster.
Relevance of carcinogenic effects / potential:
No local carcinogenic effects
Dose descriptor:
dose level: effective dose level for non-neoplastic effects
Effect level:
10 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: only one dose level tested; metaplasia and hyperplasia in the nasal epithelium of 4 out of 88 hamsters
Conclusions:
No local carcinogenic effects in hamsters at 10 ppm lifetime exposure but metaplasia and hyperplasia in the nasal cavity in 4 out of 88 animals.
Executive summary:

The study meets generally accepted scientific standards with acceptable restrictions concerning local effects in experiment A: Partly no data or only limited documentation (e.g. test substance, control). Only males tested; restricted to local effects; no data on sacrifice of moribund animals (possible autolysis of tissues in hamsters found dead); Methods in experiment B-E insufficient (only dissecting microscope used). Data in experiment B-E are not suitable for evaluation of toxicity and carcinogenicity of formaldehyde.

Male Syrian Golden hamster were exposed to 0 or 10 ppm, 5 h/day, 5 days/week for lifetime (experiment A; 132 controls and 88 treated hamster). Histopathology of the respiratory tract revealed local effects of the nasal cavity (metaplasia and hyperplasia) in only 4 out of 88 treated animals which were not found in controls. The survival rate is significantly decreased suggesting further evidence for toxicity at 10 ppm. No tumours have been found. Although no data are available on higher dose levels, there is some evidence that hamsters seemed to be less sensitive than rats.

Conclusion: No local carcinogenic effects in hamsters at 10 ppm lifetime exposure but metaplasia and hyperplasia in the nasal cavity in 4 out of 88 animals.

Endpoint:
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Comparable to OECD guideline 453 (Partly limited documentation; e.g. no data about purity of the test substance; ophthalmoscopic examination & urine analysis not done; blood clotting not examined in haematology; limited number of organs examined [systemic toxicity can not be fully evaluate]; low number of animals concerning carcinogenicity; only males).
Reason / purpose:
reference to same study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
Deviations:
yes
Remarks:
(Ophthalmology & urine analysis not done)
GLP compliance:
not specified
Specific details on test material used for the study:
37% formalin, stabilized with 10% methanol
Source: Wako Pure Chemicals, Osaka, Japan
No further data
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
- Source: Charles River, Atsugi, Japan
- Age/weight at study initiation: 5 weeks / no data
- Acclimatization period 1 week;
- Housing conditions:
23-25°C, 50-60% rel. air humidity, 12 h light cycle; after exposure water and diet ad libitum.
Route of administration:
inhalation: gas
Type of inhalation exposure (if applicable):
whole body
Vehicle:
air
Details on exposure:
No data about temperature and rel. air humidity. Gas was generated by introduction of the aqueous formalin solution into a sprayer in a glas bottle at 70°C and the resulting vapour carried the formaldehyde to the 560 L chamber and mixed with air (no details).
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Concentration monitored by the acetone-acetyl method, twice per day.
Duration of treatment / exposure:
28 months
Frequency of treatment:
6 h/day, 5 days per week
Post exposure period:
no
Dose / conc.:
0.3 ppm (nominal)
Remarks:
0.3 ± 0.07 ppm (mean ± SD); (analytical)
Dose / conc.:
2 ppm (nominal)
Remarks:
2.17 ± 0.32 ppm (mean ± SD); (analytical)
Dose / conc.:
15 ppm (nominal)
Remarks:
14.85 ± 2.22 ppm (mean ± SD); (analytical)
No. of animals per sex per dose:
32 males per dose
Control animals:
other: concurrent control (0 ppm formaldehyde) receiving 4.2 ppm methanol (like the high dose group) and additionally a room control (rc)
Details on study design:
Subgroups of 5 rats sacrificed at month 12, 18, 24 and survivors at month 28. No post exposure observation period.
Observations and examinations performed and frequency:
- Clinical signs
Checked once a day
- Mortality: Checked daily
- Body weight: Recorded weekly
- Food consumption: Recorded weekly
- Water consumption No data
- Ophthalmoscopic examination: Not done
- Haematology: At month 12, 18, 24 and 28 blood samples collected (n=5 per time point); parameter: erythrocyte counts, haemoglobin, packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin concentration, white blood cell counts (no data on platelets).
- Clinical Chemisty
At month 12, 18, 24 and 28 blood samples collected (n=5 per time point); parameter: total protein, albumin, blood urea nitrogen, glucose, phospholipids, triglyceride, total cholesterol, alkaline phosphatise, aspartate aminotransferase, alanine aminotransferase, sodium, potassium, chloride.
- Urinalysis: Not done
Sacrifice and pathology:
- Organ Weights
Brain, heart, lung, liver, kidney, spleen, testis, adrenals weight of each rat determined.
- Necropsy performed
- Histopathology
Histopathology of nasal cavity (5 cross section levels), pituitary, thyroid, trachea, oesophagus, stomach, small and large intestine, prostate, bladder, muscle, femur, sciatic nerve, spinal cord, mesenteric lymph nodes, and gross lesions.
Other examinations:
no
Statistics:
Statistical methods: ANOVA, Fisher exact test, Bartlett's test, Dunnett's test, Kruskal-Wallis test. Level of significance: p<0.05.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
0.3-2.2 ppm: no relevant effects.
15 ppm: yellow discoloration of the fur (no adverse effect), face washing behaviour, coughing, lacrimation, nasal discharge in the 1st month (gradually decreasing after 1 month).
Mortality:
mortality observed, treatment-related
Description (incidence):
No effects at 0.3-2 ppm groups in comparison to controls but slight increase in mortality at 15 ppm.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
15 ppm: significant decrease.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
15 ppm: significant decrease.
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Description (incidence and severity):
No data
Ophthalmological findings:
not examined
Haematological findings:
no effects observed
Description (incidence and severity):
No effects detected in any treatment group.
Clinical biochemistry findings:
effects observed, treatment-related
Description (incidence and severity):
0.3-2.2 ppm: no effects.
15 ppm: decrease in triglyceride at month 12.
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
15 ppm: significant decrease in absolute and relative liver weight (but no effects in histopathology).
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
At necropsy no lesions detected except nasal tumours at 15 ppm
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
No lesions detected in any organ other than nasal cavity.

Effects in nasal cavity
0 ppm & rc: cell infiltration (5/32 & 3/32), erosion (2/32 & 2/32) edema (2/32 & 0/32); similar incidences in treatment groups.
0.3 ppm: no treatment related effects
2.2 ppm: significant increase in squamous cell metaplasia with (7/32) and without (5/32) epithelial cell hyperplasia
15 ppm: significant increase in squamous cell metaplasia with epithelial cell hyperplasia (29/32) and hyperkeratosis (26/32)
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
At necropsy no lesions detected except nasal tumours at 15 ppm

15 ppm:
Incidence of squamous cell carcinoma (SCC) in the nasal cavity
0 ppm 0/32
0.3 ppm 0/32
2.2 ppm 0/32
15 ppm 13/32
Additionally papillary hyperplasia (2/32) and squamous cell papilloma (3/32) occurred at 15 ppm. All tumours in the high dose group as well as the non-neoplastic changes were located in the respiratory epithelium of the nasal cavity.
Relevance of carcinogenic effects / potential:
Clear local carcinogenic effects in nasal cavity of rats after chronic exposure to 15 ppm, no increased tumour incidences were detected at 2.2 ppm.
Dose descriptor:
NOAEC
Effect level:
0.3 ppm (analytical)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: investigated parameters including local effects in the nasal cavity
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
LOAEC
Effect level:
2.2 ppm (analytical)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: local effects in the nasal cavity like squamous cell metaplasia and hyperplasia
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
NOAEC
Effect level:
2.2 ppm (analytical)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: no increased tumour incidences including the nasal cavity
Remarks on result:
other: Effect type: carcinogenicity
Dose descriptor:
LOAEC
Effect level:
15 ppm (analytical)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: squamous cell carcinoma in the nasal cavity
Remarks on result:
other: Effect type: carcinogenicity
Conclusions:
Inhalation exposure for 28 months induced in rats non-neoplastic effects in the respiratory epithelium of the nasal cavity at a dose level of ≥ 2.2 ppm, the NOAEC was 0.3 ppm.
Executive summary:

Study meets scientific standards and is with restrictions comparable to OECD guideline 453 (Partly limited documentation; e.g. no data about purity of the test substance; ophthalmoscopic examination & urine analysis not done; blood clotting not examined in haematology; limited number of organs examined [systemic toxicity can not be fully evaluate]; low number of animals concerning carcinogenicity; only males).

In this inhalation study 32 male F344 rats per dose were exposed to 0, 0.3, 2.2, or 15 ppm formaldehyde 6 h/day, 5 days per week for 28 months; 5 rats per dose were sacrificed after 12, 18, or 24 months of exposure (no post exposure observation period). No effects were detected concerning any measured parameter at the low and mid dose except histopathological alteration at the mid dose level in the nasal cavity.Rats exposed to 0.3 ppm for 28 months did not show any histopathological changes in the nasal cavity. At 2.2 ppm a significant increase was noted in the incidence of squamous cell metaplasia with and without hyperplasia but no carcinogenic effects. Clear local carcinogenic effects were noted at a dose level of 15 ppm. No lesions were detected in any organ other than nasal cavity. There is some evidence that the study of Kamata et al. is less suitable for deriving a LOAEL (more variable exposure concentrations than in other studies).

Conclusion: Inhalation exposure for 28 months induced in rats non-neoplastic effects in the respiratory epithelium of the nasal cavity at a dose level of ≥ 2.2 ppm, the NOAEC was 0.3 ppm. Clear local carcinogenic effects in nasal cavity of rats were reported after chronic exposure to 15 ppm.

Endpoint:
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
partly limited documentation, e.g. no details about the test substance and generation of gas; restricted to effects in the nasal cavity
Reason / purpose:
reference to same study
Principles of method if other than guideline:
The study is restricted to effects in the nasal cavity of male F344 rats exposed to formaldehyde for 24 months
GLP compliance:
not specified
Specific details on test material used for the study:
Thermal depolymerisation of paraformaldehyde
Source: Aldrich Chemicals, Milwaukee, WI, USA
No further details
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals and environmental conditions:
- Source: Charles River, Wilmington, MA, USA
- Age/weight at study initiation: 8-9 weeks / no data
- Acclimatization period 14 days;
- Housing conditions:
According to NIH guideline; tap water and certified diet ad libitum (not during exposure), no further data.
Route of administration:
inhalation: gas
Type of inhalation exposure (if applicable):
whole body
Vehicle:
other: nitrogen gas/air
Details on exposure:
No data about temperature and rel. air humidity. Gas was generated by thermal depolymerisation of paraformaldehyde and nitrogen gas carried the formaldehyde to the 8 m³ chamber and mixed with air (no details).
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Concentration monitored by the IR spectrophotometer at least once per hour.
Duration of treatment / exposure:
24 months
Frequency of treatment:
6 h/day, 5 days per week
Post exposure period:
no post exposure observation period
Dose / conc.:
0.7 ppm (nominal)
Remarks:
0.69 ± 0.05 ppm (mean ± SD); (analytical)
Dose / conc.:
2 ppm (nominal)
Remarks:
2.05 ± 0.15 ppm (mean ± SD); (analytical)
Dose / conc.:
6 ppm (nominal)
Remarks:
6.01 ± 0.33 ppm (mean ± SD); (analytical)
Dose / conc.:
10 ppm (nominal)
Remarks:
9.93 ± 0.44 (mean ± SD); (analytical)
Dose / conc.:
15 ppm (nominal)
Remarks:
14.96 ± 0.80 ppm (mean ± SD); (analytical)
No. of animals per sex per dose:
90-147 males per dose (see results)
Control animals:
yes, sham-exposed
Observations and examinations performed and frequency:
- Mortality: checked daily
Sacrifice and pathology:
Histopathology of nasal cavity (several cross section levels).
Other examinations:
Autoradiography of the nasal cavity:
Interim sacrifice after 3, 6, 12, 18 months, 6 male rats per dose were labelled with 3H-thymidine continuously (osmotic mini-pump) during the last 5 days of exposure. Quantitative analysis of cell proliferation.
Statistics:
Suitable statistical methods used for evaluation (Cox's method for pairwise comparison; Dunn test, McNemar's test). Level of significance: p<0.05.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
No data except yellow discoloration of the fur (no adverse effect) and naso-lacrimal duct occlusion due to tumour formation in high dose rats.
Mortality:
mortality observed, treatment-related
Description (incidence):
No effects at 0.7-10 ppm. Significant decrease in survival at 15 ppm
Body weight and weight changes:
not specified
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Histopathology of the nasal cavity
0 ppm: No effects on the epithelium of the nasal cavity. 2/90 rats with squamous cell carcinoma originating from buccal cells (not considered to be treatment related)
0.7 and 2 ppm: no lesions in the nasal cavity
6 ppm: mixed cell infiltrate, squamous metaplasia, hyperplasia in the anterior part of the nasal cavity
10 ppm: additionally nasal turbinate adhesions and degeneration of olfactory epithelium
15 ppm: more severe effects than at 10 ppm; distortion and destruction of nasoturbinate architecture.
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Incidence of squamous cell carcinoma (SCC) in the nasal cavity
0 ppm 0/90
0.7 ppm 0/90
2 ppm 0/96
6 ppm 1/90
10 ppm 20/90
15 ppm 69/147
Most of SCC were detected in lateral meatus or mid-septum or in other words significantly more SCCs were found in the anterior sample site of the nasal cavity.
Rhabdomyosarcoma was detected in 1/90 at 10 ppm and 1/147 at 15 ppm and same incidence for nasal adenosarcoma. No polyploidy adenoma were detected at <= 6 ppm. 5/90 rats of the 10 ppm group and 14/147 rats of the 15 ppm group revealed this tumour type, most of them located in or adjacent to the lateral meatus.
Other effects:
effects observed, non-treatment-related
Description (incidence and severity):
Cell proliferation
No treatment-induced increase in cell proliferation indices at 0.7, 2 or 6 ppm were reported, dose dependent effect only at >=10 ppm.
Relevance of carcinogenic effects / potential:
Clearly carcinogenic effects in the nasal cavity of rats at a dose level of 10 ppm in a chronic inhalation study.
Dose descriptor:
NOAEC
Effect level:
2 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: local effects in the nasal cavity
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
LOAEC
Effect level:
6 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: local effects in the nasal cavity (mixed cell infiltrate, squamous metaplasia, hyperplasia in the anterior part of the nasal cavity)
Remarks on result:
other: Effect type: toxicity
Dose descriptor:
NOAEC
Effect level:
6 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: local neoplastic effects in the nasal cavity (however, 1/90 males showed a squamous cell carcinoma)
Remarks on result:
other: Effect type: carcinogenicity
Dose descriptor:
LOAEC
Effect level:
10 ppm (nominal)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: Sharp rise of tumor incidences in the nasal cavity like squamous cell carcinoma (20/90) and other tumor types
Remarks on result:
other: Effect type: carcinogenicity
Conclusions:
Inhalation exposure for 2 years induced local non-neoplastic effects in the nasal cavity of rats at a dose level of 6 ppm, the NOAEC was 2 ppm.
Executive summary:

The study meets scientific standards with acceptable restrictions (partly limited documentation, e.g. no details about the test substance and generation of gas); restricted to effects in the nasal cavity.

In this long-term inhalation study 90 -147 male F344 rats per dose were exposed (whole body) to 0, 0.7, 2, 6, 10, 15 ppm formaldehyde gas 6 h/day, 5 days per week for 24 months. Rats were sacrificed immediately after the exposure period and histopathology of the nasal cavity performed. Rats exposed to 0.7 or 2 ppm for 2 years did not show any histopathological changes in the nasal cavity and no effects on cell proliferation index. Non-neoplastic effects were detected at a dose level of 6 ppm (mixed cell infiltrate, squamous metaplasia, hyperplasia in the anterior part of the nasal cavity) as well as a minimal carcinogenic response (squamous cell carcinoma in 1/90). A sharp increase in tumour incidences in the nasal cavity (mainly squamous cell carcinoma) was reported at 10 and 15 ppm. Dose dependent effects on cell proliferation were detected also only at >=10 ppm.

Conclusion: Inhalation exposure for 2 years induced local non-neoplastic effects in the nasal cavity of rats at a dose level of 6 ppm, the NOAEC was 2 ppm; clearly carcinogenic effects were found at a dose level of 10 ppm.

Endpoint:
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
only one dose tested; rhinitis also in controls suggesting infection; only males ; restricted to respiratory tract and a few other organs; partly limited documentation; reliable concerning effects in the respiratory tract posterior to the nasal cavity (not examined in other studies presented in Section 7.7)
Principles of method if other than guideline:
Carcinogenicity study in rats using lifetime inhalation exposure of one dose level
GLP compliance:
not specified
Specific details on test material used for the study:
Source: Fisher Scientific Co
purified paraformaldehyde
no further details available
Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals and environmental conditions:
at initiation 9 weeks old, body weight 316 ± 19 g
diet and water ad libitum, not during exposure
Route of administration:
inhalation
Type of inhalation exposure (if applicable):
whole body
Vehicle:
air
Details on exposure:
exposed in 1.3 m³ chamber; formaldehyde vapour was entrained in air passing over a slurry of heated (75-90°C) paraformaldehyde
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
every 30 minutes concentration measured by chromotropic acid method
Duration of treatment / exposure:
lifetime
Frequency of treatment:
5 d/w, 6 h/d
Post exposure period:
no
Dose / conc.:
14.8 ppm (analytical)
Remarks:
± 2.1 ppm (analytical)
No. of animals per sex per dose:
100 males
Control animals:
yes, concurrent no treatment
yes, sham-exposed
Details on study design:
Post-exposure period: none
Observations and examinations performed and frequency:
clinical signs recorded daily
body weight monthly
Sacrifice and pathology:
rats allowed to die naturally or were killed when moribund
Complete necropsy
Histopathology of nasal cavity, lung, trachea, larynx, liver, kidneys, testes.
Other examinations:
no
Clinical signs:
not specified
Mortality:
mortality observed, treatment-related
Description (incidence):
Significantly increased mortality rate
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Significant decrease in body weight gain
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
In 21 rats epithelial hyperplasia was also detected in larynx (control n=2) and trachea (control n=6) and squamous metaplasia in larynx (n=4, not in control) and trachea (n=7, not in control).
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Malignant tumours were recorded in the nasal cavity of 40% of exposed rats (1 fibrosarcoma, 1 mixed carcinoma and 38 squamous cell carcinomas) but none in controls. An incidence of 10% polyps or papillomas (0 in controls) was also observed. Incidences of other tumours were comparable in both groups.
Relevance of carcinogenic effects / potential:
After chronic inhalation exposure in male rats neoplastic effects were restricted to the nasal cavity, no tumours were detected in larynx, trachea or lung.
Dose descriptor:
other: dose effective in induction of neoplasia
Effect level:
15 ppm (analytical)
Based on:
test mat.
Sex:
male
Basis for effect level:
other: mainly squamous cell carcinoma in the nasal cavity (one dose tested)

Incidences of non-neoplastic and neoplastic effects in the respiratory tract of male rats exposed lifetime to 15 ppm

Number of rats with specified effect

Effect

15 ppm formaldehyde (n=100)

Shame-exposed control (n=99)

Untreated control (n=99)

Larynx hyperplasia

21

2

2

Larynx squamous metaplasia

4

0

0

Trachea hyperplasia

21

6

2

Trachea squamous metaplasia

7

0

0

Effects in nasal mucosa

Rhinitis

74

72

70

Epithelial or squamoushyperplasia

57

51

45

Squamous metaplasia

60

5

6

Polyps or papillomas

10

0

0

Squamous cell carcinoma

38

0

0

Mixed carcinoma

1

0

0

Fibrosarcoma

1

0

0

No data about significance (but clear increase in incidences)

Conclusions:
Beside effects in the nasal cavity after chronic exposure to 15 ppm hyperplasia and squamous metaplasia (low incidence) was found in larynx and trachea of male rats.
Executive summary:

Study meets scientific standards with acceptable restrictions (only one dose tested; rhinitis also in controls suggesting infection; only males ; restricted to respiratory tract and a few other organs; partly limited documentation); reliable concerning effects in the respiratory tract posterior to the nasal cavity (not examined in other studies presented in Section 7.7).

Onehundred male Sprague-Dawley rats per dose level were exposed lifetime to 0 or 15 ppm formaldehyde (6 h/day, 5 days/week). A significant decrease in body weight gain and significantly increased mortality rate were reported. Histopathology revealed increased incidences in epithelial hyperplasia as well as squamous metaplasia (low incidence) in larynx and trachea. Malignant tumours were recorded in the nasal cavity of 40% of exposed rats (1 fibrosarcoma, 1 mixed carcinoma and 38 squamous cell carcinomas in 100 rats) but none in controls. An incidence of 10% polyps or papillomas (0 in controls) was also observed. Incidences of other tumours were comparable in both groups.

Conclusion: After chronic inhalation exposure in male rats neoplastic effects were restricted to the nasal cavity, no tumours were detected in larynx, trachea or lung. Beside effects in the nasal cavity, hyperplasia and squamous metaplasia (low incidence) was found in larynx and trachea.

Carcinogenicity: via dermal route

Link to relevant study records
Reference
Endpoint:
carcinogenicity: dermal
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
restrictions: 30 female animals per group
Principles of method if other than guideline:
Initiation-promotion study in mice using the dermal route
GLP compliance:
not specified
Specific details on test material used for the study:
paraformaldehyde
Source: Celanese Chemical Company
Purity: 96.81 wt. % paraformaldehyde and 3.18 wt. % water
Stock solutions of formaldehyde in water prepared (20% for further dilution with acetone) by solving paraformaldehyde powder in distilled water heated to 75°C
Standard solutions analyzed according to modified NIOSH methods: no formaldehyde-acetone condensation
Species:
mouse
Strain:
CD-1
Sex:
female
Details on test animals and environmental conditions:
Source: Charles River Breeding Laboratories
housed singly
acclimatisation period 2 weeks
randomisation
certified diet and tap water ad libitum
no further data
Route of administration:
dermal
Vehicle:
other: acetone:water 50:50
Details on exposure:
Formaldehyde solutions were mixed with acetone in a 50:50 acetone:water ratio to facilitate spreading the test material on the skin. The backs of all mice clipped (not abraded; repeated approximately once a week);
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Standard solutions analyzed according to modified NIOSH methods
Duration of treatment / exposure:
26 weeks
Frequency of treatment:
3 times a week
Post exposure period:
26 weeks
Dose / conc.:
10 other: %
Remarks:
for initiation (nominal in water)
Dose / conc.:
0.1 other: %
Remarks:
for promotion (nominal in water)
Dose / conc.:
0.5 other: %
Remarks:
for promotion (nominal in water)
Dose / conc.:
1 other: %
Remarks:
for promotion (nominal in water)
No. of animals per sex per dose:
30 females
Control animals:
yes
Details on study design:
A single application of an initiation solution followed two weeks later by application of appropriate promoter solutions; promoter treatments were administered three times a week for 26 weeks followed by a post exposure observation period of 26 weeks.
Dosing regimen is presented in the Table below
Observations and examinations performed and frequency:
Clinical signs recorded once daily; observation of first skin nodules and location of each nodule for each mouse recorded. Nodules persisting for >= 30 days were evaluated; total number of nodules per mouse determined.
Body weight measured once every 2 weeks, monthly during post exposure observation period
Sacrifice and pathology:
Necropsy performed
At termination after the 26 weeks observation period representative sections of skin from the test site evaluated microscopically along with all skin nodules present at sacrifice. Skin sections and nodules from mice sacrificed in extremis or found dead during the study were also evaluated microscopically except one mouse.
The following organs were macroscopically examined in survivors and mice found dead/moribund: stomach, adrenals, duodenum-cecum-colon, liver, kidneys, heart, brain, esophagus, spleen, borie marrow, thymus, lung, eyes, lymph node(mediastinal), thyroid and trachea (not evaluated microscopically due to the absence of grossly apparent effects in all but the positive controls).
Other examinations:
no
Statistics:
A one-way analysis of variance; Fisher's Exact Test. Significance was judged at the p < 0.05 level of probability.
Clinical signs:
effects observed, non-treatment-related
Description (incidence and severity):
No treatment related differences in clinical signs.
Mortality:
mortality observed, treatment-related
Description (incidence):
Mortality increased in the positive control BaP/TPA due to ulcerated skin tumors.
Body weight and weight changes:
no effects observed
Description (incidence and severity):
No effects on body weight.
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
not specified
Gross pathological findings:
not specified
Histopathological findings: non-neoplastic:
not specified
Histopathological findings: neoplastic:
effects observed, non-treatment-related
Description (incidence and severity):
Formaldehyde did not initiate or promote skin tumorigenesis.
Formaldehyde did not alter the latency time to first tumour.
Relevance of carcinogenic effects / potential:
Formaldehyde did not initiate or promote skin tumorigenesis and did not alter the latency time to first tumour in an initiation-promotion study in mice after repeated dermal application at a concentration of 1%.
Dose descriptor:
NOAEC
Effect level:
1 other: % in vehicle (1 mg in 100 µL/mouse/application)
Based on:
test mat.
Sex:
female
Basis for effect level:
other: highest concentration tested; no promoting activity although "mild irritating" effects after 2 weeks of treatment in a pretest

No tumours (0/28) were observed in both the groups exposed to formaldehyde (FA) as initiator plus acetone (promotor), or 10% FA (initiator) plus 1% FA (promotor).Tumor incidences in groups initiated with BaP and treated with FA as promoter were 1/25 (4%), 2/28 (7%), and 7/27 (26%) at FA concentrations of 1%, 0.5%, and 0.1%, respectively. Initiation with BaP followed by promotion with acetone as well as initiation with acetone and promotion with TPA resulted in tumour incidences of 3/27 (11%) in both cases. Five of 28 mice (18%) treated with FA (initiator) and TPA (promotor) had skin nodules. The highest tumour incidence (28/29; 97%) was observed in the group initiated with BaP and treated with TPA as promotor.
Most of the nodules were benign tumours (keratocanthomas or papillomas; malignant tumours were histopathologically diagnosed in the BaP+TPA group, only (squamous cell carcinomas). No statistically significant differences were observed between the treated groups and appropriate controls in groups exposed to formaldehyde. According to the authors, these results suggest that formaldehyde did not initiate or promote skin tumorigenesis in minimally irritating concentrations (in a preliminary test, a concentration of 10% FA was determined as moderately irritating, 1% caused mild irritation, 0.5% was slightly irritating, 0.1% induced no local effects; no details given).

The average time to the first nodule was 110 days for mice treated with BaP (initiator) plus TPA (promoter), 355 in acetone/TPA, 341 in FA/TPA, 370 in BaP/1% FA, 361 in BaP/0.5% FA, 338 in BaP/0.1% FA, 361 in BaP/acetone; no tumours were detected in FA/acetone or FA/1% FA. There were no statistically significant differences found in the mean days to first observed nodule in any test group when compared with the appropriate negative control group.

Executive summary:

Study meets scientific standards with acceptable restrictions (30 female animals per group).

Thirty female CD-1 mice per group received a single dermal application of an initiation solution followed two weeks later by application of appropriate promoter solutions; the promoter treatments were administered three times a week for 26 weeks followed by a post exposure observation period of 26 weeks. Nine different dose regimens were performed including appropriate negative and positive controls (BaP for initiation and TPA for promotion). Initiation with formaldehyde (FA) was done with  

5 mg FA in 50 µL vehicle (10% FA solution, irritant) and promotion with 1, 0.5, or 0.1 mg FA in 100 µL vehicle (concentration 1, 0.5, 0.1%, respectively; slight local irritation at 0.5%). Formaldehyde did not initiate or promote skin tumorigenesis. Formaldehyde did not alter the latency time to first tumour. The negative and positive controls were valid. Malignant tumours were induced only in the positive control (initiatorBaP/ promoter TPA).

Conclusion: Formaldehyde did not initiate or promote skin tumorigenesis and did not alter the latency time to first tumour in an initiation-promotion study in mice after repeated dermal application at a concentration of 1%.

Additional information

Data on experimental animals

Oral exposure

Sufficient data are available on long-term drinking water studies in rats. No data are available on other species. In a combined chronic toxicity/carcinogenicity study (Til et al., 1989; all parameters tested as recommended in OECD Guideline 453) 70 male and 70 female Wistar rats per dose (subgroups of 10 rats/sex/dose killed 12 or 18 months after start of exposure) received via the drinking water 0, 1.2, 15, 82 mg/kg bw/day (males) or 0, 1.8, 21, 109 mg/kg bw/day (females) for 105 weeks (concentration: 0, 0.002, 0.026, 0.19%). At the high dose body weight gain was decreased in males & females and food and water consumption decreased. Other parameters (except pathology) were not altered. Pathological alterations in the kidney were related to reduced water intake and are indirectly treatment related. No systemic tumour formation was found. Treatment related lesions were detected in the forestomach (focal papillary epithelial hyperplasia, ulceration and hyperkeratosis) and the glandular stomach (chronic atrophic gastritis, ulceration and hyperplasia) of males and females in the high dose group. No gastric tumours were induced. In conclusion, hyperplasia in forestomach and glandular stomach but no tumour formation were detected after chronic exposure in rats via the drinking water. Non-neoplastic local effects in the stomach were reported at a concentration of 0.19% corresponding to 82 mg/kg bw/d in males and 109 mg/kg bw/d in females; the NOAEC is 0.026% corresponding to 15 mg/kg bw/d in males and 21 mg/kg bw/d in females. This study did not provide any evidence of carcinogenicity in rats after oral administration of formaldehyde.

These results were supported by the drinking water study of Tobe et al. (1989). Local effects in the forestomach were detected in rats after oral exposure to >= 0.10% in the drinking water (50 mg/kg bw/day) for 2 years; the NOAEC was 0.02% in the drinking water (10 mg/kg bw/ day). At the high dose level of 300 mg/kg bw/day corresponding to a concentration of 0.50% hyperplasia in forestomach and glandular stomach was found but no tumour formation in rats after chronic exposure (low number of animals).

Ambiguous results were presented in the drinking water study by Soffritti et al. (1989, 2002). This study is not sufficient for evaluation of systemic and local carcinogenic effects due to several deficiencies which are also mentioned by IARC (2006):

- no statistics given for the hemolymphoreticular tumours

- with regard to the Soffritti et al. (2002) the IARC working group performed a statistical analysis in comparison to the methanol control group. For hemolymphoreticular tumours a statistically significant increase was only found for the high dose males

- pooling of lymphomas and leukaemias (designated as hemolymphoreticular tumours)

- no reporting of non-neoplastic lesions

- absence of information on historical incidences of hemolymphoreticular tumours. This was also addressed in a letter to the editor by Feron et al., (1990) criticizing the report of Soffritti et al. (1989): the historical control data of the rat colony used revealed a broad variation and the finding may well have been a chance effect unrelated to treatment. No reply of Soffritti to this criticism is available

- in spite of the extensive histopathological evaluation done initially, in 1989 the total number of animals with hemolymphoreticular tumours increased from 79 (in 1989) to 150 (in 2002). But the investigators have not given any explanation/justification. for this massive discrepancy reported in the two publications on the same study.

- In addition, recently severe doubts were published concerning the scientific robustness of studies from this laboratory (Schoeb et al., 2009; Ward and Alden, 2009). The critique is mainly related to the observation of increased incidences of lymphomas after exposure to several chemicals reported in the decade between 1995 and 2005, and the validity of studies conducted by the Soffritti laboratory is questioned especially regarding the health status and historical control tumour incidences of the animals used.

In an initiation/promotion study (Takahashi et al., 1986) male Wistar rats (n=10-30) were initiated with 100 mg/L MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) in the drinking water (ad libitum) plus 10% sodium chloride in the diet (ad libitum) for 8 weeks followed by promotion for 32 weeks with 0.5% formaldehyde in the drinking water (n=17 for evaluation). Additional control groups received only initiation (n=30) or only 0.5% formaldehyde or only vehicle. All groups were sacrificed after 40 weeks. Body weight gain was decreased in all treatment groups compared to vehicle control suggesting toxic effects of initiation and promotion procedure. In accord with other long-term drinking water studies, local lesions in forestomach (papilloma, erosion and ulcer at the limiting ridge of fundic mucosa) and glandular stomach (hyperplasia) were induced by formaldehyde but no malignant tumours developed. Forestomach papillomas were found in 8/10 formaldehyde-only treated rats and in none of the control animals. The occurrence of forestomach papillomas, especially after such a short treatment period, is in clear contrast to the findings of Til et al. (1989) and Tobe et al. (1989). This discrepancy was discussed by Til et al. (1989) as being possibly related to the use of different criteria for the classification of a lesion as papilloma or as papillary epithelial hyperplasia. At that time widely accepted criteria to distinguish both alterations were not available. Promotion by formaldehyde in initiated rats increased hyperplastic lesions in the glandular stomach but did not significantly increase the total number of adenocarcinomas in the gastroduodenal epithelium. Conclusion: In rats oral exposure to 0.5% formaldehyde in the drinking water induced local lesions in stomach but there was no clear evidence for promoting activity.

In summary, the weight of evidence shows that formaldehyde does not induce systemic or local carcinogenic effects after oral exposure.  

Dermal exposure

No studies according to current guidelines were published. The available data on this endpoint showed local irritation but no carcinogenic effects. In an initiation/promotion study (Krivanek et al., 1983) 30 female CD-1 mice per group received a single dermal application of an initiation solution followed two weeks later by application of appropriate promoter solutions; the promoter treatments were administered three times a week for 26 weeks followed by a post exposure observation period of 26 weeks. Nine different dose regimens were performed including appropriate negative and positive controls (BaP for initiation and TPA for promotion). Initiation with formaldehyde was done with 5 mg formaldehyde in 50 μL vehicle (10% solution, irritant) and promotion with 1, 0.5, or 0.1 mg formaldehyde in 100 μL vehicle (concentration 1, 0.5, 0.1%, respectively; slight local irritation at 0.5%). Formaldehyde did not initiate or promote skin tumourigenesis. Formaldehyde did not alter the latency time to first tumour. The negative and positive controls were valid. Malignant tumours were induced only in the positive control (initiator BaP/ promoter TPA). In conclusion, formaldehyde did not initiate or promote skin tumourigenesis in mice and did not alter the latency time to first tumour in an initiation-promotion study at a concentration of 1%.

The initiation-promotion study of Iversen (1986) in mice (suggesting reduced latency time to first tumour) is insufficient for evaluation of carcinogenic or promoting effects.

In summary, the limited data indicate that formaldehyde does not act as a complete carcinogen or as a promoter or initiator on the skin after topical application.

Inhalation exposure

Data on rats

There is clear evidence from chronic inhalation studies in rats that formaldehyde causes tumours in the nasal cavity of males and females; the most prominent tumour type identified in the nasal cavity was the squamous cell carcinoma, occasionally also other tumour types were found in the nasal cavity. A sharp increase of these tumour incidences was evident at concentrations >6 ppm indicating a non-linear dose response. In all studies cited, no systemic or carcinogenic effects were detected at other sites.

In a study comparable to OECD guideline 453 (CIIT, 1981; Kerns et al., 1983) inhalation exposure of male and female F344 rats for 2 years at dose levels of 0, 2, 6, 15 ppm (120 rats per sex per dose; 24 months exposure, 6 h per day, 5 days per week; post exposure period 6 months; interim sacrifices) resulted exclusively in local effects of the nasal cavity and of the proximal trachea in males and females. Only non-neoplastic effects were reported in the high dose group in the proximal trachea but a high incidence in squamous cell carcinomas of the nasal cavity (51/120 males and 52/120 females). Carcinogenic effects in the mid dose group (squamous cell carcinomas in nasal cavity of 1 male and 1 female) are not of statistical significance but possibly of toxicological relevance (extremely low background incidence, in IARC 1976: Pathology of tumours in laboratory animals; according to Borman et al. [Pathology of the Fisher rat, Academic Press, 1990] the spontaneous tumour incidence is 1/1936 in untreated male F344 rats and 2/1949 in corn oil controls, no spontaneous incidences in females). At 2 ppm purulent rhinitis, epithelial dysplasia, and squamous metaplasia were present in the anterior part of the nasal cavity. Dysplasia occurred earlier than metaplasia. Non-neoplastic effects in the mid dose group like dysplasia and squamous cell metaplasia in the nasal cavity occurred also in more posterior parts or the nasal cavity. Reversibility of these non-neoplastic effects have been shown after 3 months post exposure period. At month 27 there was a significant decrease in the incidence of squamous metaplasia at all exposure concentrations regressing predominantly from the more posterior parts of the nose to the anterior sections (see Section Repeated dose toxicity). In summary, non-neoplastic local effects in the nasal cavity of rats were reported even at the low dose level of 2 ppm in a long-term inhalation study in rats; tumours in the nasal cavity were found at a dose level of 15 ppm.

In the chronic study of Monticello et al. (1996; restricted to effects in the nasal cavity) in male F344 rats (0, 0.7, 2, 6, 10, 15 ppm, 6 h/day, 5 days/week) inhalation exposure for 2 years induced local non-neoplastic effects in the nasal cavity of rats at a dose level of 6 ppm, the NOAEC was 2 ppm; clearly carcinogenic effects were found at a dose level of 10 and 15 ppm.

In the inhalation study of Kamata and coworkers (1997; only 32 rats per dose and interim sacrifice) male F344 were exposed 6 h/day, 5 days per week for 28 months. Rats exposed to 0.3 ppm for 28 months did not show any histopathological changes in the nasal cavity. At 2.2 ppm a significant increase was noted in the incidence of squamous cell metaplasia with and without hyperplasia but no carcinogenic effects. Clear local carcinogenic effects were noted at a dose level of 15 ppm.

In male Sprague-Dawley rats (n=100 per dose level, lifetime exposure to 0 or 15 ppm, 6 h/day, 5 days/week) incidences in epithelial hyperplasia as well as squamous metaplasia (low incidence) in larynx and trachea were increased. Malignant & benign tumours were recorded in the nasal cavity of exposed rats but none in controls, no tumours were detected in larynx, trachea or lung (Sellakumar et al., 1985).  

The results in Wistar rats (low incidence at 10 ppm, Feron et al., 1988; Woutersen et al., 1989) are limited by a small group size or short exposure duration. Nevertheless, there might exist strain differences in sensitivity comparing F344 with Wistar rats.

There is also some evidence for induction of nasal tumours at 20 ppm at the end of life even after subchronic exposure periods (Feron et al., 1988). Non-neoplastic lesions induced at 10 ppm partly persisted during the life time post observation period.

Other tumour types than the squamous cell carcinoma were found in the nasal cavity: squamous cell papilloma (3/32 rats at 15 ppm, 3/32 rats; Kamata et al., 1997), rhabdomyosarcoma (1/90 at 10 ppm, 1/147 at 15 ppm; Monticello et al., 1996), adenosarcoma (1/90 at 10 ppm, 1/147 at 15 ppm; Monticello et al., 1996), fibrosarcoma (1/100at 15 ppm; Sellakumar et al., 1985), polypoid adenoma (5/90 rats at 10 ppm & 14/147 rats at 15 ppm; Monticello et al., 1996), undifferentiated carcinoma or sarcoma (2/117 at 15 ppm, CIIT, 1981). The predominant localisation of tumours (mainly the squamous cell carcinoma) in the nasal cavity was the anterior portion of the lateral side of the nasal turbinate and the adjacent lateral wall or the mid-ventral septum (CIIT, 1981).  

Data on other species

In repeated inhalation toxicity studies on mice it has been shown that the mouse is less sensitive than the rat. Generally the lesions in mice were less severe than in rats using the same experimental design (CIIT, 1981; Kerns et al., 1983). This might also be true for carcinogenic effects in long-term inhalation studies in B6C3F1 mice (CIIT, 1981; Kerns et al., 1983). Only 2 squamous cell carcinomas in the nasal cavity of male mice were detected in the high dose group (15 ppm). Location and morphology were similar to those observed in rats. However, only 25 male mice survived a minimum of 18 months in the high dose group (reduced survival not treatment-related). In females the survival was not reduced but no tumour was detected in the nasal cavity. Non-neoplastic lesions (see Section Repeated dose toxicit) like rhinitis, dysplasia, squamous metaplasia were induced, but also atrophy of olfactory epithelium with increasing exposure periods at the high dose level (NOAEC is 2 ppm and the LOAEC 6 ppm). At 27 months (3 months post exposure period) dysplastic epithelial lesions were only present in the 15 ppm group. Squamous metaplasia was not present at this time interval and the low- and intermediate-exposure groups were free of treatment-related effects.

Also hamsters were less sensitive than rats. In the long-term inhalation study on Syrian golden hamsters (Dalbey, 1982) at formaldehyde concentration of 10 ppm (5 h/d; 5 d/week) in 5% of the animals (4/88), metaplasia and hyperplasia in the nasal epithelium was found but no tumours were detected in the respiratory tract. In addition, treatment with 30 ppm (5 h/d; but only 1 day/week) did not lead to respiratory tract tumours (no further details available).

In a recent review by McGregor et al. (2007 & 2010) the authors summarised and evaluated the available experimental data. They concluded that sustained cytotoxicity and cell proliferation are key events in the proposed mechanism of action (MOA) for formaldehyde- induced nasal tumours in rats. Cytotoxicity, DPC formation, nasal epithelial cell regenerative proliferation, squamous metaplasia, and inflammation have been measured in rat studies and are considered to be site-specific, highly non-linear concentration response processes in concordance with the incidence of nasal tumours. Based on the weight of evidence, it is likely that this MOA is relevant to humans, at least qualitatively. Several epidemiological studies have indicated an increased risk of nasal cancers with formaldehyde exposure (see below). It seems unlikely for the authors that this MOA could result in increased tumour incidences at sites distant from first contact.

Data on carcinogenicity in humans

The possible association between formaldehyde exposure and cancer has been investigated in numerous epidemiological studies in occupationally-exposed humans (e.g., pathologists, anatomists, embalmers, or industrial workers). Because the International Agency for Research on Cancer (IARC) evaluated formaldehyde in 1996, 2004 and 2009 an overview on the epidemiological knowledge about the carcinogenic potential of formaldehyde is ordered in accordance to these time points. A tabulated summary from cohort studies published before 1996 is given in IUCLID Section 7.10.2. New data on risk measures from cohort studies on cancers that were published after 1996 are summarised below. Epidemiological data are also available from case-control studies. With regard to toxicokinetic data and the results in long-term laboratory animal studies most epidemiological studies focused on carcinogenic effects in the respiratory tract, the site of first contact. In addition, in three out of four recent cohort studies all cancer types are investigated (Coggon et al., 2003; Hauptmann et al., 2003 & 2004, Pinkerton et al., 2004). The overall results suggested an increased risk of cancer only at two tumour sites: the upper respiratory tract and the haematopoietic system. However, recent reassessment of the Hauptman et. al. (2003, 2004) data by the U.S. National Cancer Institute suggest these findings may not be significant (Beane-Freeman, et. al. 2009 ab) as reviewed by Marsh et. al. (2010) and supported by Bachand, et. al. (2010)

Summary Table on new data on risk measures from recent cohort studies on cancer (after 1996)

Exposed cohort Referent group

Tumour site (ICD): number of deaths

Risk measure SMR (95% CI)

Remark

Reference

7359 male & female workers at a plastic-producing plant (2735 deaths) Local county population

Nasopharynx (147): 7 Pharynx (146-149): 22 Lung (162): 262

5.00(2.01-10.3) 2.23(1.40-3.38) 1.21(1.06-1.36)

Nasopharyngeal cancer only in exposed workers, but not related to DOE and weakly related to Doe, cumulative exposure and AIE; SMR increased with TSFE

Marsh et al., (2002)

14,014 male workers at 6 British chemical factories (5185 deaths) National population

Pharynx (146-149.1): 6 Larynx (161): 7

Lung (162): 272 Leukaemia (204-208):8 Multiple myeloma (203): 7

1.91 (0.70-4.17) 1.56 (0.63-3.22) 1.58(1.40-1.78) 0.71 (0.31-1.39) 1.18 (0.48-2.44)

SMR related to men with high exposure (> 2 ppm)

Differentiation in exposure categories only for lung cancer (exposure related increase in SMR)

Coggon et al. (2003)

11039 male & female workers at 3 garment factories (2206 deaths) General population

Pharynx (146-149): 3 Lung (162): 147 Leukaemia (204-08): 17 Myeloid leukaemia (205): 9

0.64 (0.13-1.86) 0.98 (0.82-1.15) 1.78(1.04-2.86) 2.24(1.02-4.25)

MCOD analysis used for leukaemia and myeloid leukaemia, SMR related to workers exposed for ≥ 10 years

Pinkerton et al. (2004)

25619 male & female workers at 10 plants (8486 deaths) SMR: general population; RR: low exposure group This study included as Plant 1 the cohort analyzed by Marsh et al. (2002)

Nasopharynx (147): 8 Lung (162): 641 Leukaemia (204-207):65 Nasopharynx (147): 7 Nasopharynx (147): 6 Nasopharynx (147): 3 Nasopharynx (147): 2 Leukaemia (204-07): 29 Myeloid leukaemia (205): 14 Leukaemia (204-07): 17 Myeloid leukaemia (205): 9

SMR 2.10(1.05-4.21) 0.97 (0.90-1.05) 0.85 (0.67-1.09) RR 1.83 1.67 4.14 4.18 2.46(1.31-4.62) 3.46(1.29-9.43) 1.68 (0.91-3.08) 2.49(1.03-6.03)

SMRs only for nasopharyngeal cancer increased but RR also for (myeloid) leukaemia peak exposure ≥ 4 ppm* average intensity ≥ 1 ppm cumulative exposure ≥ 5.5 ppm-years* duration of exposure >15 years peak exposure ≥ 4 ppm** peak exposure ≥ 4 ppm** average intensity ≥ 1 ppm average intensity ≥ 1 ppm

Hauptmann et al. (2003) (leukaemia) & (2004) (nasopharyngeal cancer)

Due to an incomplete follow-up these studies are not reliable although used as pivotal evidence by IARC (2006)

Continuation of the data presented in Hauptmann et al; 2003; follow-up of the 25619 male & female workers through December 31, 2004

all lymphohematopoietic malignancies (200-209) 286 Hodgkin disease (201) 25 multiple myeloma (203) 48 all leukaemia (204-7) 116 myeloid leukaemia (205)44 all lymphohematopoietic malignancies (200-9) 108 Hodgkin disease (201) 11

SMR 0.94 (0.84 to 1.06) 1.42 (0.96 to 2.10) 0.94 (0.71 to 1.25) 1.02 (0.85 to 1.22) 0.90 (0.67 to 1.21) RR 1.37(1.03 -1.81) 3.69(1.31-12.02)

exposed workers, all SMRs non-significant peak exposures ≥ 4.0 ppm vs lowest peak exposure dito all other malignancies RR non-significant

Beane Freeman et al. (2009a)

CI: confidence interval; SMR: standard mortality ratio; RR: relative risk; ICD: International classification of diseases code; DOE: duration of employment; Doe: duration of exposure; TSFE: Time since first employment; AIE: average intensity of exposure; MCOD: Multiple causes of death analysis; bold type: trend test significant

Nasopharyngeal cancer

Indication for an excess of death from nasopharyngeal tumours in industrial workers (Blair et al., 1986; Collins et al., 1988; Marsh et al., 1996; all three studies refer to the same study population) and embalmers (Hayes et al., 1990) was presented in former cohort studies and a proportionate incidence study (Hansen & Olsen, 1995; SPIR 1.3 for nasopharynx and SPIR 2.3 for nasal cavity tumours); however, no increased risk was detected in other studies (see IUCLID Section 7.10.2 - Additional Information, Table 1).

Some evidence for an association between formaldehyde exposure and nasopharyngeal tumours was also reported by Marsh et al. (2002). Although the SMR for all pharyngeal cancer and nasopharyngeal cancer were significantly increased, no clear relation to the level of exposure was found when different exposure categories were considered (see Table above). Most pharyngeal cancer (PC) and nasopharyngeal cancer (NPC) occurred in workers hired between 1947 and 1956 (higher exposure levels presumed). But short-term workers showed a higher death rate of PC or NPC than workers employed for > 1 year. Neither PC nor NPC were associated with duration of employment but SMR (as well as number of deaths) increased with time since first employment. Only little evidence of increasing mortality risks with increasing duration of exposure, cumulative exposure or AIE (average intensity of exposure) was seen. There is some evidence for increasing risks for PC with increasing duration of exposure with average exposure >0.2 or 0.7 ppm. Concerning especially the NPC data it should be noted that subgroup size of 1-3 cases resulted in limitation of the statistical power.

Evidence for an association between formaldehyde exposure and nasopharyngeal cancers came from a publication of Hauptmann et al. (2004). The cohort study of Hauptmann et al. (2004) is the largest and most informative study in industrial workers concerning the number of study subjects in the cohort. It includes as Plant 1 the cohort analyzed by Marsh et al. (2002). Hauptmann et al .(2004) have shown a statistically significant exposure-response relationship for peak exposure and cumulative exposure compared with an internal control group (see Summary Table above). The peak exposures are defined as the highest peak exposure ever identified during work history (see the critical discussion of this unusual exposure metric in Marsh and Youk, 2005). In comparison with the general population, the SMR for nasopharyngeal tumour was also increased(SMR = 1.97; 0.95-CI: 0.94-4.14).The cohort from Hauptmann et al. (2004) has been re-evaluated by Marsh and Youk (2005). They point out that 6 of the 10 deaths due to nasopharyngeal cancer occurred only in Plant 1, while the remaining four cases occurred individually in four of the other nine plants. Furthermore a comprehensive exposure analysis for the cases in Plant 1 showed no clear relation to exposure as had already been pointed out in Marsh et al. (2002). Only three of the cases were exposed to formaldehyde longer than one year and each has had low average intensity of exposure.

Marsh and Youk (2005) hypothesised that the increased risks for nasopharyngeal cancer in Plant 1 are due to occupational or non-occupational exposure to risk factors outside Plant 1 (see study by Marsh et al 2007b below for follow-up on this hypothesis).

Similar criticism came from Tarone & McLaughlin (2005). In their re-evaluation of the data presented by Hauptmann et al. (2004) the calculated SMR for nasopharyngeal cancer in exposed workers in Plant 1 was 9.1 (95% CI: 3.3-19.8) (unexposed workers SMR 0.0) but in Plant 2-10 the SMR in exposed workers was 0.6 (95% CI: 0.1-2.3) (unexposed workers SMR 1.9). They argued that the absence of an increased risk in exposed workers of Plants 2-10 and the magnitude of the differences in SMRs raises serious questions about the interpretation of the results. However, Tarone and McLaughlin focussed on ever/never exposure comparison (all exposure categories combined) and compared with external rates. In their reply Hauptmann et al. (2005) suggested the internal comparison (used in Hauptmann et al., 2004) for comparison which is more informative without a healthy worker bias. However, even the comparison with an external group resulted in increased SMRs for Plant 1 and Plants 2-10 at the highest level for all four exposure categories (Hauptmann et al., 2005). Furthermore, the homogeneity of SMRs for Plant 1 versus Plants 2-10 was not rejected, except peak exposure indicating no clear pattern of risk heterogeneity between Plant1 and Plants 2-10 (Hauptmann et al., 2005).The authors stated that all six workers with nasopharyngeal cancer in Plant 1 had been in the highest peak exposure category of ≥ 4 ppm (compare with criticism presented by Marsh & Youk (2005, Section Human data).

Marsh and co-workers (Marsh et al., 2007a, Section Human data) substantiated their criticism in a recent re-evaluation of the Hauptmann study (Hauptmann et al., 2004).They performed two types of re-analyses with focus on peak exposure and NPC mortality. First, they performed a formal interaction analysis to examine whether the risk estimates varied considerably by plant (“effect modification”). The results substantiated the arguments of Tarone and McLaughlin (2005): the findings are heterogeneous (plant 1 vs. plant 2-10) and cannot be validly combined into one estimate and, thus, cannot be generalized to other populations. The interaction analysis also showed convincingly that the model applied by Hauptmann et al. (2004) was inappropriate. Marsh and co-workers suggested using these extended modeling techniques in future updates of the NCI cohort study to avoid model misspecifications. Second, they performed a sensitivity analysis to study whether the results reported by Hauptmann et al (2004) suffer from uncertainties not covered by the reported confidence intervals due to the low number of cases (“small sample bias”). Their Monte-Carlo sensitivity analyses revealed substantial instability problems with the exposure-response relationships related to Plant 1. The authors stated that their results do not support a causal association with formaldehyde exposure and nasopharyngeal cancer. Furthermore, Marsh et al. (2007b) investigated the possibility that the large NPC mortality excess among workers of plant 1 (see also criticism by Marsh & Youk, 2005) may be related to occupational factors external to this study plant (Wallingford cohort). The results in their nested case-control study suggested that the NPC mortality excess in the Wallingford cohort may reflect the influence of external employment in the local metal industries that entailed possible exposures to risk factors for upper respiratory tract cancer like sulphuric acid mist, mineral acids and metal dusts. Marsh and co-workers suggested further updates of the Hauptmann study that should include co-exposure data on silver smithing and other metal work for all 10 plants. This might help to explain the findings for NPC in plant 1 in comparison with the other 9 plants.

Importantly, Beane-Freeman et al. (2009a) recently reported that 1006 deaths were not included in the data analysed by Hauptmann et al. (2004). An explanation could not be given why these 1006 deaths were not included. Marsh et al (2010) described and discussed this incomplete follow-up in the National Cancer Institute's formaldehyde worker study and the impact on subsequent re-analyses and causal evaluations.The addition of these deaths increased mortality by 10.5% for the study group. However, the deaths were not missed at random. The percent increase in corrected numbers of deaths among “unexposed” subjects is approximately two times greater than that observed among “exposed” subjects for all deaths, all cancer deaths and all solid cancers. This may have a pronounced effect on the dose-response relationships as they have been overestimated potentially by Hauptmann et al (2004). Furthermore, according to the tables published in Beane-Freeman et al (2009b) the corrected increase for total deaths by exposure status equals 995, not 1,006 as described by Beane-Freeman (2009a). The noted difference creates doubt whether all ascertainment errors were addressed by the NCI working group as the consistent differential change in cause-specific numbers of deaths by exposure category cannot likely be explained as a chance occurrence thereby raising serious doubt about the validity of the Hauptmann (2004) analysis. Aside from the combined category “all solid cancers”, the NCI working group has not reported corrected estimates for any site-specific cancer mortality corresponding to solid tumour types, particulary NPC.

Thus, Marsh and co-workers asked for a prompt corrigendum of the 2004 publication by the NCI working group since this study has played such a prominent role in causal evaluations. Finally it should be noted that an update of the Hauptmann et al. (2004) study on NPC has been initiated by NCI. Thereby the mortality from solid cancers that was analysed by Hauptmann through 1994 will be traced for another 10 years and include the results from the 995/1006 additional cases. A final assessment of the mortality by NPC should wait for the results of this NCI industry cohort update and clarifications of the NCI data base.

Other studies do not support a causal relationship between formaldehyde and NPC deaths. Collins et al (1997) summarized all studies published up to 1996 and found 14 cohort studies showing RR=1.0 (0.95-CI: 0.5-1.8). Aside from the NCI formaldehyde industry cohort study two other big cohort studies were performed after 1996. A slight but statistically not significant increase in pharyngeal cancer was found in the study of Coggon et al. (2003) in 14014 workers from 6 British plants. While only one death from NPC was observed with 2.0 expected, leading to an SMR=0.5 (0.95-CI: 0.01-2.79), the man had not worked in a job with high formaldehyde exposure. No nasal or nasopharyngeal tumours were found in the cohort (11039 workers from 3 plants) studied by Pinkerton et al. (2004) and only 3 deaths were related to cancer of the pharynx clearly limiting the statistical power of this study to investigate this endpoint . Indication for an association between formaldehyde exposure and nasopharyngeal tumours was presented in case-control studies. Several studies on nasopharyngeal cancer found an increased risk for an exposure to formaldehyde, mainly in subjects with the highest probability, level or duration of exposure (Vaughan et al., 1986b & 2000; Roush et al., 1987; West et al., 1993; Hildesheim et al., 2001) but two other studies did not show such an association (Vaughan et al., 1986a; Armstrong et al., 2000).

Collins et al (1997) summarized all studies published up to 1996 and found 15 case-control studies with an overall OR=1.3 (0.95-CI: 0.9-2.1).Vaughn et al 2000 (USA: 196 cases / 244 controls: OR= 1.3, 0.95-CI: 0.8-2.1) and Hildesheim et al 2001(Taiwan: 375 cases / 325 controls: OR= 1.4, 0.95-CI: 0.9-2.2) were the two case-control studies that were published afterwards and reported similar findings. However, although they showed some evidence of an increase in NPC risk the exposure levels in these studies were uncertain. Thus, these investigations are clearly limited.

In the meta-analysis presented by Bosetti et al. (2007) nine deaths from nasopharyngeal cancer in three cohorts of industry workers yielded a pooled SMR of 1.33, which declined to 0.49 after excluding six cases from one US plant (plant 1, see Hauptmann et al., 2004, Marsh et al 2007): the non-significantly increased SMR for nasopharyngeal cancer among industry workers is attributable to a cluster of deaths in a single plant. Thus, they confirmed the observation of Marsh et al. (2005), Tarone and McLaughlin (2005)and Marsh et al. (2007a). Similarly, after analysing cohort and case-control studies Duhayon et al. (2008) concluded that the human studies fail to raise a convincing conclusion concerning NPC mortality being related to formaldehyde.

Bachand et al. (2010) performed another statistical summary of epidemiological studies and found that estimates for NPCs were not elevated after excluding a single plant with an unexplained cluster (cohort RR = 0.72, 95% CI: 0.40, 1.28), again giving support to the observations by Marsh et al. (2005), Tarone and McLaughlin (2005) and Marsh et al. (2007a). The summary estimate was increased for case-control studies overall, but the summary OR for smoking-adjusted studies was 1.10 (95% CI: 0.80, 1.50). Bachand et al. concluded that there is little support for a causal relationship between formaldehyde exposure and nasopharyngeal cancer.

In a review summarizing the current knowledge regarding the epidemiology of NPC the major risk factors were identified by Chang and Adami (2006), i.e. elevated antibody titers against the Epstein-Barr virus, a family history of NPC,consumption of salt-preserved fish and certain human leucocyte antigen class I genotypes. They concluded that the epidemiological evidence for an increased risk of NPC following workplace exposure is limited and that occupational or non-occupational exposures other than formaldehyde may have been responsible for excess NPC mortality.

Summary and evaluation of Nasopharyngeal cancer (NPC)

Regarding the association between formaldehyde exposure and solid tumours IARC (2006) concluded:

- sufficient evidence for NPC was mainly based on the NCI industrial cohort study (Hauptmann et al. 2004) and supported by positive findings from other studies

- limited evidence for sinonasal cancer

- no evidence for other sites (incl. oral cavity, oro- and hypopharynx, pancreas, larynx, lung, brain).

The IARC (2006) evaluation for NPC was confirmed by an IARC working group in October 2009 (Baan et al., 2009).

A literature search after the last IUCLID update was carried out up to April 20, 2015.  

As NPC is one of the critical tumor types possibly associated with formaldehyde exposure, some studies on NPC not directly related to formaldehyde are briefly mentioned here.

Liu et al. (2012) used a screening program for NPC based on detection of antigens against the Epstein-Barr virus, examination of the nasopharynx and lymphatic palpation. Among 28,688 individuals from a high risk area in China, NPC was detected in 41 persons (0.18%) and in 28 of these in an early stage. Xu et al. (2012) carried out a case-control study to investigate potential NPC risk factors in a high risk area of China with 1316 NPC cases and 1571 controls from the same region, 1657 controls from another high risk area, and 1961 controls from a low risk area. Smoking was the only life style factor significantly associated with NPC and was also linked to Epstein-Barr virus seropositivity among the control populations. Specific workplace related analyses were not carried out. Fachiroh et al. (2012) studied life style and genetic factors among 681 cases and 1078 controls from Thailand. Again this study did not include analyses of the workplaces. Frequent consumption of fermented vegetables, smoking, and some specific genetic variants were significantly associated with NPC. Polesel et al. (2013) studied the risk for NPC in relation to dietary habits in 198 NPC cases and 594 controls from Italy, a low risk region for NPC. Elevated vegetable consumption was significantly inversely related to NPC and this effect was particularly strong for yellow and red pigmented vegetables. Elevated egg consumption was significantly associated with NPC. Xue et al. (2013) conducted a meta-analysis on studies over the last 30 years and identified 28 case-control and 4 cohort studies with a total of 10274 NPC cases and 415266 controls. A significant risk for NPC was identified with an OR of 1.6 (95% CI 1.38; 1.87) with a robust association for smokers compared to never smokers.

Beane-Freeman et al (2013, key) further extended the follow-up of the NCI cohort of workers in FA industries (n = 25 619) through 2004. During 998 239 person-years, 13 951 deaths occurred. With one additional death, albeit occurring in the lowest exposure category, previously observed excesses for nasopharyngeal cancer (n = 10) persisted for peak, average intensity and cumulative exposure; RRs in the highest exposure categories were 7.66 (95 % CI: 0.94–62.34), P-trend = 0.005, 11.54 (95 % CI: 1.38–96.81), P-trend = 0.09, and 2.94 (95 % CI: 0.65–13.28), P-trend = 0.06, respectively. For all cancer, solid tumours and lung cancer, standardised mortality ratios (SMRs) among exposed workers were reported to be elevated, but internal analyses, as described by the authors, revealed no positive associations with FA exposure.

A follow-up through December 2012 was conducted in the British (UK) cohort from six factories comprising 14 008 men in the period 1941–2012 (Coggon et al 2014, key). In the period, 7 378 men had died. 3,991 were at some time highly exposed. In the whole population, the standardised mortality ratio [SMRs (95 % CI)] for all cancers [1.10 (1.06–1.15)], stomach [1.29 (1.11–1.49)], rectum [1.23 (1.01–1.49)], and for lung cancer [1.26 (1.17–1.35)] was significantly increased based on the national death rate for England and Wales. There was no excess mortality from NPC; the only death occurred in a man with low/moderate exposure (1.7 deaths expected for exposures above background). Additionally, the authors included a nested case-control analysis of cancer in the upper airways, larynx, mouth, pharynx, tongue, and for all leukaemia and myeloid leukaemia. ORs for these cancers were independent of the duration of the exposure. The authors ascribed the increases in risk estimates to non-occupational confounding factors, which may include smoking and socioeconomic factors and concluded that the study provided no evidence that FA posed an increased hazard either of upper airway cancer. It was noted that the study was not able to take smoking and socioeconomic factors into account.

A follow-up has been conducted on the US NIOSH garment industry cohort (Meyers et al 2013, key), which is one of the three largest prospective cohorts. The study comprised 11 043 workers. Causes of death were obtained from 99.7 % (3 904) of the identified deaths. About 77 % had year of first exposure in 1970 or earlier. In the early 1980s, personal FA sampling was performed among 549 employees. The geometric mean FA concentration was 0.15 ppm with a geometric standard deviation of 1.90. The SMRs were similar to that of the US population for all cancers, for buccal cavity and pharyngeal cancers and for respiratory cancers. The authors concluded that the study showed little evidence for an increased risk of mortality from buccal cavity, pharyngeal (including nasopharyngeal) or respiratory cancer.

An Italian cohort with subjects employed in a factory producing laminate plastic, decorative papers and craft papers, using phenolic and melamine resins, has been established Pira et al. (2014, supporting). The major risk was considered to be FA exposure, but FA concentrations were not reported. The cohort comprised 2750 employees from the period 1947 to 31 May 2011, who have been employed at least 180 days. Data on survival (80.3%) and death (16.6%, N=457) were collected. Cause of death could not be retrieved for 26 out of 457 (5.7%) deceased employees. Person-years of observation were 70,933. Expected number of death (E) and SMRs were obtained by comparison with the regional deaths rates. The risk for all cancers was not increased (149; 0.80 (0.68-0.94) and there was a non-significantly increased risk for oral and pharynx cancer (9; 1.49 (0.68-2.82) and for bladder cancer (10; 1.51 (0.72-2.77)). The study has a long follow-up period, but a limitation is the lack of quantitative FA exposures and the relatively small cohort.

Airway cancers associated with FA exposures were studied in a Finnish cohort with 1.2 million employees (Siew et al 2012, key). All men born between 1906 and 1945, and employed during 1970 were included. The follow-up was in the Finnish Cancer Register for nasal cancer (292 cases), cancer of the nasopharynx (149 cases) and lung cancer (30 137 cases) during the period 1971–1995. The Finnish job-exposure matrix was used to estimate exposures. Duration of exposure was estimated from census data. A latency period of 20 years was accepted. Number of exposed cases (N), relative risk (RR) obtained by comparison with unexposed, and 95 percent confidence intervals were estimated (N; RR (95 % CI)). The risks of nasal cancers (17; 1.1 (0.6–1.9), nasal squamous cell carcinoma (9; 1.0 (0.4–2.0)) and nasopharyngeal cancer (5; 0.9 (0.3–2.2)) were not increased. The risk was slightly increased for lung cancer (1 831; 1.2 (1.1–1.3)). However, the risk in the highest exposure group (≥ 1 ppm) was not increased. Thus, the authors considered the increased risk to be due to residual confounding effects of smoking and co-exposures, including asbestos and crystalline silica. FA exposures were below 1 ppm in most occupations. Only flour layers, and varnishers and lacquers had average exposures at 1 ppm. Overall, this study found no increase in portal-of-entry cancer at low FA concentrations in occupational settings.

In conclusion, the weight of evidence from the most recent studies does not give any additional support for an association between formaldehyde and NPC and the classification of IARC as a group 1 carcinogen for this tumor type.

Therefore, the strength of the epidemiological data for NPC is not sufficient for a classification of formaldehyde as a human carcinogen within the EU regulatory framework taking into account that

- only in one of the three large cohort studies an association between formaldehyde and NPC was found

- this association was restricted to one specific plant

- there is evidence that pre-employment factors may have been the cause for NPC formation in this plant

- the stability of the statistical analysis and the appropriateness of the statistical model of Hauptmann et al. (2004) may be questioned

- unaccounted deaths raise doubt about the mortality analysis of Hauptmann et al. (2004)

- two recent meta-analyses and a general review on NPCs (not cited in IARC 2006) do not substantiate the association between formaldehyde exposure and NPC

- the ongoing update by NCI for another 10 years survival should be waited for before coming to a final conclusion.

Sinonasal cancer

In a pooled analysis of 12 case control studies conducted in 7 countries and adjusted for age, study and other occupational exposure an exposure related increase in the risk of sinonasal cancer, particularly adenocarcinoma, was reported (Luce et al., 2002). Similar results were presented by T’Mannetje et al. (1999). In a Danish study, the odds ratios for squamous cell carcinoma in the nasal cavity or para-nasal sinus were increased (Olsen & Asnaes, 1986). In contrast to these case-control studies, the recently published cohort studies (Coggon et al., 2003; Pinkerton et al., 2004; and Hauptmann et al., 2004) reported no excess of this cancer type.

Lung

In most cohort studies no association between exposure and lung cancer was found. However, in two recent studies (Coggon et al., 2003; Marsh et al., 2002 Section Human data) some evidence for an association was provided by SMR analysis. However, both studies did not adjust for smoking and Coggon et al 2003 could not identify any trend in lung cancer mortality across metrics of formaldehyde exposure. No excess in mortality from lung cancer was recorded by Pinkerton et al. (2004, Section Human data) and also by Hauptmann et al. (2004, Section Human data), representing the most detailed and informative investigations concerning this tumour site. In conclusion: there is no evidence on exposure-related increase in tumours of the lung. Furthermore, in case-control studies there has been no increase in lung cancer except for one study (Gerin et al., 1989) which reported an association between lung adenocarcinoma and formaldehyde exposure.

In the literature search after the last IUCLID update carried out up to April 20, 2015 some further studies on lung cancer were identified:

Regarding lung cancer, IARC (2012) noted that there are statistical significant associations but the results are inconsistent. Therefore, no classification for lung cancer was assigned to formaldehyde.

There are numerous epidemiological studies among textile workers on lung cancer indicating reduced risks related to cotton dust exposure presumably due endotoxin exposure. Checkoway et al. (2011, supporting) investigated by a nested case-cohort study within 267400 women textile workers potential associations with other exposures like wool and synthetic fibres, formaldehyde, silica, dyes, and metals. 628 lung cancer cases were compared to a reference subcohort of 3188 workers. A job-exposure matrix was constructed and age/smoking-adjusted hazard ratios (HR) were calculated. No associations for lung cancer were found for most agents, but increased risks, although imprecise, were observed for ≥10 years of exposure to silica (HR 3.5, 95% CI 1.0-13) and for ≥10 years of exposure to formaldehyde (HR 2.1, 95% CI 0.4-11). The authors note that there is only weak prior evidence supporting an association between lung cancer and formaldehyde.

Mahboubi et al. (2013, supporting) conducted two population-based case-control studies in Montreal, Canada, on lung cancer. Identical interviews by questionnaire for the 2 studies were carried out in 1976-1986 and 1996-2002. In all, 2060 lung cancer cases were compared to 2046 population controls. About 25% of the subjects were exposed to formaldehyde. The adjusted OR for formaldehyde was 1.06 (95% CI 0.89-1.27) comparing ever vs. never exposed subjects. No marked increase in lung cancer risk related to occupational formaldehyde exposure was observed. But the authors note that the subjects were mainly exposed to low concentrations: for example, only 3.7-8% of the subjects were exposed to substantial exposure levels as defined by authors for the cumulative exposure index.

Pharyngeal cancer

A study obtained in the literature search up to April 20 2015, is mentioned here. Paget-Bailly et al. (2012, supporting) carried out a metaanalysis on cancer of the laryx based 99 publications on chemicals with at least 10 available publications. Significantly increased meta-relative risks were identified for polycyclic aromatic hydrocarbons, engine exhaust, textile dust, and working in rubber industry. Formaldehyde was not significantly associated with laryngeal cancer on the basis of 11 studies.

Leukaemia

Most studies published before 1996 focused on cancer of the respiratory tract because a potential effect of formaldehyde on the respiratory organs appeared to be biologically plausible. On the same grounds no or only weak evidence for an association between formaldehyde exposure and increased mortalities from systemic cancer in humans was expected. However, in two out of three recent studies on industrial workers [see Section Human data and Summary Table above] some evidence for an association between formaldehyde exposure and leukaemia has been reported by two US investigations (Pinkerton et al. 2004; Hauptmann et al. 2003 - however, see discussion below on the continuation of this study by Beane Freeman et al., 2009a,b) but not by the large British study (Coggon et al. 2003).

In an update of the garment worker study (Pinkerton et al. 2004) leukaemia (all types, 24 deaths observed) and myeloid leukaemia (15 deaths observed), identified by a multiple-cause mortality assessment, were non-significantly increased in comparison to the general population. Investigating the exposure metric surrogates “duration of exposure” and “time since first exposure” there was no clear trend in all leukaemias but some indication of a trend in myeloid leukaemia. In summary, the study of Pinkerton et al. (2004) lent some support to the hypothesis of a possible link between formaldehyde exposure and the occurrence of leukaemia, in particular myeloid leukaemia. However, no exposure concentration data was available for analysis in this study.

Coggon et al. (2003) identified 31 leukaemia deaths and reported a decreased risk in the high exposure group, i.e., in jobs with formaldehyde concentration levels estimated to be higher than 2 ppm (SMR = 0.71, 95% confidence interval 0.31-1.39). For comparison, the SMR for all leukaemias was calculated to be 1 for those jobs with exposures less than 2 ppm. However, the exposure assessment was crude and myeloid leukaemias were not evaluated separately.

Influential results from the NCI cohort study analyses were published by Hauptmann et al. (2003) who were able to make extensive use of individual estimates of exposure levels to formaldehyde in their analyses. The authors documented 69 leukaemia cases including 30 deaths from myeloid leukaemia. For all leukaemias, the authors reported a significant increase in the relative risk for peak exposure and the trend was highly significant (referent group: low exposure level; but no analysis was carried out by comparison to the general population). This trend was driven by clearly elevated relative risks for death from myeloid leukaemia (again, highly significant across peak exposure categories). In 2004 a working Group at IARC concluded (IARC 2006): “In summary, there is strong but not sufficient evidence for a causal association between leukaemia and occupational exposure to formaldehyde. These findings fall slightly short of being fully persuasive because of some limitations in the findings from the cohorts of industrial and garment workers in the USA and because they conflict with the non-positive findings from the British cohort of industrial workers. Thus, this judgement by the working group at IARC was driven a lot by the results published by Hauptmann et al. (2003).

As already described and discussed in the chapter on nasopharyngeal cancers Beane-Freeman et al. (2009a, b) reported that 1006 / 995 deaths were not included in the data analysed by Hauptmann et al. (2003). An analysis of the corrected data by Beane-Freeman et al. (2009b) showed that the results and conclusions published in Hauptmann et al (2003) were invalid. The addition of 995 deaths to the NCI cohort increased total mortality by 10.5 percent and produced notable corrections to the results published by Hauptmann et al (2003). A detailed discussion is given in Marsh et al (2010). For leukaemia, the correction of number of deaths by 11 percent resulted from seven additional deaths that occurred only among subjects in the lowest category (>0 to 1.9 ppm) of “peak exposure” used by NCI as the referent for relative risk calculations. Hauptmann et al.(2003) reported that the relative risk for leukaemia mortality among those workers classified as having the peak exposure to formaldehyde was 2.46 (95% confidence interval (CI): 1.31-4.62). Upon reanalysis, the corrected relative risk estimate for this outcome was 1.60 (95% CI: 0.90-2.82) (Beane Freeman et al., 2009b). This addition of seven leukaemia deaths to the referent category (Beane Freeman et al., 2009b) considerably attenuated the exposure-response relationship for highest ever peak exposure to formaldehyde and leukaemia, resulting in a trend test p-value of 0.0942 for exposed groups only (the original reported p-value for this trend test based on exposed groups only was 0.004). These new, corrected findings for leukaemia (Beane Freeman et al., 2009b) supported the results of a reanalysis of the 1994 NCI data (Hauptmann et al., 2003) published in Marsh and Youk 2004. This reanalysis showed that the exposure-response relationship for leukaemia originally reported by Hauptmann et al. (2003) was due largely to a deficit in deaths among the low or unexposed subgroups. The uncorrected standardised mortality ratios (SMRs) calculated by Marsh and Youk (2004) were inordinately low and statistically significant for both the unexposed category (SMR=0.38, 95% CI= 0.10-0.97) and lowest peak exposure (>0-1.9 ppm) category (SMR=0.50, 95%CI=0.28-0.81). The most recent NCI results for leukaemia yielded an even more attenuated exposure-response relationship for leukaemia resulting in a trend test p-value of 0.12 among exposed workers only for mortality follow-up through 2004 (Beane Freeman et al., 2009a, the authors now documented 123 leukaemia cases including 48 deaths from myeloid leukaemia). Clearly, the incorrect data for leukaemia in the original 1994 follow-up of the NCI cohort study created misleading evidence for a highly significant exposure-response relationship between peak formaldehyde exposure and leukaemia. All findings about myeloid leukaemia are non-significant in the updated study (Beane Freeman et al., 2009a) although the number of cases available for analysis increased by more than 150%. Only the original (i.e. uncorrected) NCI cohort data were available in 2004 when the International Agency for Research on Cancer (IARC, 2006) reclassified formaldehyde as a known human carcinogen (Group 1) based on findings for NPC and to a lesser extent on NCI’s findings for leukaemia reported by Hauptmann et al.(2003, 2004).

The study of Beane Freeman et al. (2009a) is a continuation of the cohort study presented in Hauptmann et al. (2003). The authors extended the follow-up through December 31, 2004, for 25619 workers employed at 10 formaldehyde-using or formaldehyde producing plants before 1966. Relative risk (RR) estimates and 95% confidence intervals (CI) were calculated to examine associations between quantitative formaldehyde exposure estimates (peak exposure, average intensity and cumulative exposure) and death from lymphohaematopoietic malignancies. Confounding by exposure to other possible leukaemiogenic substances was assessed. There were statistically significant increased risks for the highest vs lowest peak formaldehyde exposure category ( ≥ 4 parts per million [ppm] vs >0 to < 2.0 ppm) and all lymphohaematopoietic malignancies (RR = 1.37; 95% CI = 1.03 to 1.81, P trend = .02) and Hodgkin lymphoma (RR = 3.96; 95% CI = 1.31 to 12.02, P trend = .01). Statistically nonsignificant associations were observed for multiple myeloma (RR = 2.04; 95% CI = 1.01 to 4.12, P trend > .50), all leukaemia (RR = 1.42; 95% CI = 0.92 to 2.18, P trend = .12), and myeloid leukaemia (RR = 1.78; 95% CI = 0.87 to 3.64, P trend = .13). However, the unexposed showed a significantly elevated multiple myeloma mortality when compared to the low exposed (RR=2.74, 95% CI = 1.18 to 6.37) and SMRs were below 1 among the exposed for all lymphohaematopoietic malignancies, multiple myeloma and myeloid leukaemia. An unexceptional SMR was found among the exposed for all leukaemias and a non-significantly elevated SMR for Hodgkin lymphoma. There was little evidence of association for any lymphohaematopoietic malignancy with average intensity or cumulative exposure at the end of follow-up in 2004. Time period analyses have shown that disease associations varied over time. For peak exposure, the highest formaldehyde-related risks for myeloid leukaemia occurred before 1980, but trend tests attained statistical significance in 1990 only. After the mid-1990s, the formaldehyde-related risk of myeloid leukaemia declined. Data suggested that largest risks occurred closer in time to relevant exposure. However, Marsh and Youk 2004, Fig. 2 described the distribution of leukaemia deaths by time since highest peak exposure (data of Hauptmann et al 2003) and showed that the majority of cases occurred after more than 20 years of latency. In conclusion, the updated analyses of the NCI cohort (Beane Freeman et al. 2009a, b) reduced concern about a possible causal association between exposure to formaldehyde and lymphohaematopoietic malignancies, in particular for myeloid leukaemia. Due to open questions regarding data validity and appropriate statistical modeling re-analyses should be waited for that may help clarify the situation (Marsh et al 2010).  

Collins and Lineker (2004) performed an overview of all epidemiological studies that investigated formaldehyde exposure and leukaemia risk. They evaluated 8 studies on industrial workers, 7 studies on embalmers and 3 studies on pathologists/anatomists. The authors calculated a summary RR of 1.1 (0.95-CI: 1.0-1.2). The embalmer studies showed a significantly elevated risk of RR=1.6 (0.95-CI: 1.2-2.0) and a borderline statistically significant elevation was found for pathologists/anatomists (RR =1.4, 95%CI 1.0-1.9). Industrial workers showed no excess: RR = 0.9 (95% CI 0.8–1.0). However, according to IARC 1995 higher peak and time weighted average exposure concentrations of formaldehyde were expected to occur among industrial workers. The authors discussed that increased leukaemia rates in embalmer, pathologist or anatomist could be related to exposures other than formaldehyde.

An updated overview of all epidemiological studies published through February 2007 was performed by Bosetti et al (2008).They differentiated between studies of industrial workers and professionals (pathologists, anatomists and embalmers) exposed to formaldehyde. The overall RR for industrial workers was 0.85 (95%-CI: 0.74-0.96) when analysing all lymphatic and hematopoietic cancers, and 0.90 (95%-CI:0.75-1.07) for leukaemia. The overall RR for professionals was 1.31 (95%-CI: 1.16 -1.48) for all lymphatic and hematopoietic cancers, and 1.39 (95%-CI: 1.15-1.68) for leukaemia. Therefore, the authors found modestly elevated risks for lymphohematopoietic neoplasms in professionals, but not industry workers – in support of the result presented by Collins and Lineker (2004).

Zhang et al (2009a) focused on occupations known to have high formaldehyde exposure, analysing a subset of studies used in Collins and Lineker (2004) and Bosetti et al. (2008). Summary relative risks (RRs) were elevated in 15 studies of leukaemia (RR=1.54; confidence interval (CI), 1.18-2.00) with the highest relative risks seen in six studies for myeloid leukaemia (RR=1.90; 95% CI: 1.31 -2.76). All six studies of myeloid leukaemia had relative risks of ≥ 1.4 for the highest exposure categories. The authors concluded that these results of the meta-analysis suggested that formaldehyde causes leukaemia, specifically myeloid leukaemia. However, in the discussion the authors stated that the question of biological plausibility remains and requires further investigation. They proposed potential mechanisms and hypothesized that formaldehyde may act on bone marrow directly or, alternatively, may cause leukaemia by damaging the hematopoietic stem or early progenitor cells that are located in the circulating blood or nasal passages, which then travel to the bone marrow and become leukemic stem cells.

In contrast, other scientists stated that no plausible mechanism for the induction of leukaemia in humans is found (Section Mode of action). According to Golden et al. (2006), there is no evidence that formaldehyde reaches the bone marrow or has toxic effects in the bone marrow and there is no credible evidence that formaldehyde causes leukaemia in experimental animals. In accord, Pyatt et al. (2008) concluded that existing science does not support the proposed hypothetical mode of action as a logical explanation for proposing that formaldehyde is a realistic etiological factor for any lymphohematopoietic malignancy. Mechanistic considerations in carcinogenicity were also evaluated in IARC (2006); a summary is presented in IUCLID Section 7.12. The IARC working group considered several possible mechanisms for the induction of human leukaemia such as clastogenic damage to circulating stem cells. But they were not aware of any good rodent models that simulate the occurrence of acute myeloid leukaemia in humans. Therefore it was not possible to identify a mechanism for this tumour type. In addition to these mechanistic considerations, the epidemiological approach chosen by Zhang et al. (2009a) appears to be difficult to interpret because the authors combined highest exposure categories of very different meaning from independently designed studies. See the methods paper by Berlin et al. (Berlin JA, Longnecker MP, Greenland S. 1993. Meta analysis of epidemiologic dose-response data. Epidemiology 4(3): 218-228) for a critical discussion of such an approach and for possible solutions how to combine results from studies with differently categorized exposure metrics.

The most recent meta-analysis on epidemiological studies investigating the potential link between formaldehyde and cancers was published by Bachand et al (2010). The authors tried to understand differences between already published overviews and identified characteristics of the original investigations that were used to explore biases. They investigated leukaemia (overall) and three subcategories (myeloid, lymphatic/lymphocytic, and other/unspecified). In contrast to the other meta analyses described and discussed before these authors included the new NCI follow-up study by Beane Freeman et al (2009a) and did not rely on the misleading results of Hauptmann et al. (2003). Therefore, this detailed analysis appears to be the most reliable. They reported the following findings:

- For leukaemias, the summary relative risk (RR) was 1.05 (95% CI: 0.93, 1.20) for cohort studies, and the summary odds ratio (OR) was 0.99 (95% CI: 0.71, 1.37) for case-control studies.

- Based on cohort and case-control studies, no significant differences were seen by leukaemia subtype, job type, publication period, or region.

Previous meta-analyses showed elevated summary estimates for leukaemia; however, these analyses included results from proportionate mortality studies and did not explore other factors that could influence or confound results. Proportionate mortality studies have clear methodological limitations when used to evaluate causality (Rothman KJ, Greenland S, Lash TL.,2008. Modern epidemiology. 3 edn. Philadelphia: Lippincott Williams & Wilkins, p.97-99).

- By limiting analyses to stronger case-control and cohort study designs, considering the effects of smoking, the meta-analyses provided little support for a causal relationship between formaldehyde exposure and leukaemia.

However, following a meeting on 20-27 October 2009 in Lyon, an IARC working group now stated (Baan et al 2009) that there is sufficient evidence in humans for a causal association of formaldehyde exposure and myeloid leukaemia. They argued that the epidemiological evidence has become stronger: a recent study (Hauptmann et al. 2009) found that embalming was significantly associated with an increased risk for myeloid leukaemia, with significant trends for cumulative years of embalming and for increasing peak formaldehyde exposure. Moreover,Zhang et al (2010) observed haematological changes in peripheral blood and chromosomal aberrations in formaldehyde exposed Chinese workers. Whereas the study by Zhang et al. (2010) is discussed in the endpoint summary on genetic toxicity Hauptmann et al (2009) will be described and critically discussed in the following.

Hauptmann et al (2009) reported on a NCI case-control study based on three registries listing professionals employed in the funeral industry. Vital statistics offices documented 6808 deaths between 1960 and 1986 for the subjects enumerated on these three lists. In addition to vital status cause of death was reported to NCI. The case-control study was based on 168 lymphohematopoetic deaths (incl 34 myeloid leukaemias), 48 deaths from brain tumours and 265 deceased matched control subjects among these 6808 deaths. The controls were chosen in such a way that their death was attributed to other causes of death than those of interest while excluding respiratory and nervous system as causes. Furthermore, controls were matched to cases by data source, sex, date of birth and date of death. Interviews with next of kin and co-workers were performed between 1990 and1992 to collect basic exposure information for the deceased cases and controls. In these interviews data on work practices, tobacco use and characteristics of the study subjects were gathered. Quantitative exposure assessment was based on a model developed at the Cincinnati College of Mortuary Sciences that linked rate of embalming, effect of ventilation, and concentration of formaldehyde solution to formaldehyde concentration in the air. When the qualitative data from the interviews with next of kin and former co-workers were transformed into quantitative input data with the aim to apply the model it became obvious that necessary details in about 50% of the subjects were missing: there were no data available to calculate peak, average or cumulative exposures to formaldehyde for about half of the study group. The authors used unconditional logistic regression adjusting for matching variables and smoking to analyze the data. The reported results focused on myeloid leukaemia and embalming:

- Ever vs. never embalming was associated with a clearly elevated odds ratio of 11.2 although the significantly elevated estimate was rather imprecise (95%-CI: 1.3 - 95.6)

- Positive trends were observed with duration and number of embalmings

- Positive trends were not found for cumulative exposure but were found withaverage and peak formaldehyde exposure metrics.

No noteworthy associations were observed with other lymphohematopoietic malignancies or brain cancer. The estimated effects of duration of embalming and of peak formaldehyde exposure on myeloid leukaemia mortality were emphasized by the IARC working group as important findings (Baan et al 2009).

However, the design of the investigation suffered from obvious weaknesses: no incidence density sampling of controls was performed and only deceased controls were enrolled for study (see for a discussion the textbook by Rothman et al. 2008; reference see above). Moreover, mean average and peak exposures were reported to be identical among myeloid leukaemias and controls according to the description given in Table 2 in Hauptmann et al (2009), just duration and number of embalmings and cumulative exposures were described as higher among cases. Thus, it is unclear how robust the reported findings of an association between peak formaldehyde exposures and myeloid leukaemia are. Next, the race distribution was clearly different between myeloid leukaemias and controls (see Table 1 of Hauptmann et al. 2009) but this difference was ignored in the analyses and the discussions although race was always adjusted for in the NCI cohort analyses (Hauptmann et al. 2003, Beane Freeman et al. 2009a). Furthermore, the calendar year of first employment in the funeral industry clearly differed between myeloid leukaemia cases and controls but this was not adjusted for in the analyses (cases began work more often before WWII when exposures may have been qualitatively different than later). Hauptmann et al. (2009) performed sensitivity analyses to estimate the effect of the large amount of missing data in exposure assessment on the study findings: all risk estimates were attenuated when missing data were taken into account. Moreover, trends were no longer significant or positive ininternal analyses - that is the model type emphasized by Hauptmann et al (2003) and Hauptmann et al (2004). In addition, the reported trend in formaldehyde peak exposure was based on only one case among the controls. Therefore, the authors performed an additional analysis using alarger referent group. Again, there was no trend found in internal analyses.Therefore, this case-control study of Hauptmann et al. (2009) is clearly limited and should not be understood as proof for a causal association of formaldehyde exposure and myeloid leukaemia mortality. 

In summary, the extensions and re-evaluations of the NCI cohort study, the results of a large British study and clear limitations of the NCI embalmer case-control study shed doubt on the decision of an IARC’s working group that there is a causal association between formaldehyde exposure and leukaemia mortality, in particular myeloid leukaemia mortality (Baan et al 2009). Results from a recent meta-analysis (Bachand et al 2010) support this point of view.

The strength of the epidemiological leukaemia data is not sufficient for a classification of formaldehyde as a human carcinogen within the EU regulatory framework taking into account that there is no consistency between the different epidemiological studies:

- the statistically significant trends in the NCI cohort study as originally reported by Hauptmann et al. (2003) were misleading and were withdrawn by Beane Freeman et al (2009)

- the NCI embalmer case-control study is clearly limited

- an association between formaldehyde and leukaemia generally was not found for industrial workers within the meta-analyses, but some indication of a relationship for professionals (e.g. embalmers, pathologists). However, for these professionals confounding factors cannot be excluded. And these findings could not be repeated when focusing on the stronger designs of case-control and cohort studies.

- there is no mechanism for induction of leukaemia that is broadly accepted by the scientific community: the mechanism proposed by Zhang et al. (2010; see IUCLID Section 7.10.2 and mode of action in IUCLID Section 7.12) should only be considered as being hypothetical.

- in carcinogenicity bioassays with inhalation exposure leukaemia was not observed in any species

A literature search after the last IUCLID update was carried out up to April 20, 2015.

In the follow-up on the US NIOSH garment industry cohort described abovewith 11,043 workers (Meyers et al 2013, key) the SMRs were similar to those of the US population for all cancers as well as for lympho-haematopoietic cancers (leukaemias, Hodgkin disease, non-Hodgkin lymphoma, and multiple myeloma). Stratifying SMRs for “year of first exposure” (< 1963, 1963–1970, ≥ 1971) did not show significant associations for lympho-haematopoietic cancers, Associations between “duration of FA exposures” (< 3, 3–9, ≥ 10 years) and risks of cancer were studied with SMRs and SRRs. There was no exposure-dependent increase in risks for lympho-haematopoietic cancers and non-Hodgkin lymphoma. The risks increased with the length of the exposures for leukaemia, myeloid leukaemia and acute myeloid leukaemia, but were not statistically significant. For multiple myeloma, the SMRs for the exposure groups were 1.16 (0.50–2.29), 2.03 (1.01–3.64) and 0.64 (0.17–1.64), respectively, and the SRRs were 1.00 (reference), 1.22 (0.46–3.26) and 0.28 (0.08–099), respectively. Nevertheless, among persons with ≥ 10 years of exposure and ≥ 20 years since first exposures, the risk for leukaemia (23 deaths, SMR: 1.74 (1.10–2.60)) was significantly increased when multiple causes of death were considered. Additionally, the association between duration of exposure and leukaemia (36 cases) and myeloid leukaemia (21 cases) was studied using four multivariate Poisson regression models (adjusted for age, year of birth and years since first exposure), where exposures were either untransformed or transformed (log, square root, and categorical (< 1.6 (reference), 1.6– < 6.5, 6.5– < 16, 16– < 19 and ≥ 19 years)). Only the untransformed model for leukaemia and the categorical model for myeloid leukaemia were statistically significant. Nevertheless, for leukaemia and myeloid leukaemia, the rate ratio was significantly increased in the fourth category (4.56 (1.30–16.2) and 6.42 (1.40–32.2), respectively), but not for the other (2th, 3th and 5th) categories. In total,the myeloid leukemia mortality was elevated but not the overall leukemia mortality compared to the US population. When analyzing SMRs by year of first exposure, exposure duration, and time since first exposure, the overall leukemia mortality showed a significant association with increasing exposure duration. The authors concluded that that this update continued to show limited evidence for leukemia, but the extended follow-up did not strengthen the formerly observe associations.

In the follow-up of the British (UK) cohort study described above in the period 1941–2012 (Coggon et al 2014, key), no significant increase was seen for the different hematopoietic malignancies. The cohort was stratified for levels of exposure, where the exposure was >2 ppm in the high exposure group. No increase was seen for non-Hodgkin lymphoma [0.90 (0.48–1.55)], multiple myeloma [1.18 (0.57–2.18)], leukaemia [0.82 (0.44–1.41)] and myeloid leukaemia 0.93 [0.40–1.82)]. Exposure in the high exposure group was further stratified for duration of exposure (<1 year, 1–14 years and ≥ 15 years) and the SMRs were largely independent of the length of the exposure period. Additionally, the authors included a nested case-control analysis for all leukaemia and myeloid leukaemia. ORs for these cancers were independent of the duration of the exposure.

Also, in the Italian cohort study described above (Pira et al. 2014, supporting) the incidences for lymphoma, myeloma, leukaemia, and for all lympho-haematopoietic neoplasms were not increased. The study has a long follow-up period, but a limitation is the lack of quantitative FA exposures. Several studies analysed the epidemiological evidence for lymphohematopoetic cancer including leukemia. A meta-analysis of Schwilket al(2010, supporting)focussed on high-exposure groups and myeloid leukaemia. The analysis included two large studies in particular: one involving > 25 000 workers in US FA industries and the other involving a cohort of > 13 000 funeral directors and embalmers. FA was found associated with increased risks of leukaemia (RR = 1.53; 95 % CI = 1.11–2.21; p = 0.005; 14 studies), specifically myeloid leukaemia (RR = 2.47; 95 % CI = 1.42–4.27; p = 0.001; 4 studies). This study was interpreted by the authors to provide evidence of an increased myeloid leukaemia risk with high exposures to FA.The analysis has been considered to suffer from methodological shortcomings similar to the analysis of Zhang et al. (2009a) because it did not use all available information. The chosen highest exposure cut points varied across the combined studies, which introduced heterogeneity; the homogeneity tests used in the study were considered insensitive. Predictive intervals are recommended instead of confidence intervals and the findings of elevated leukaemia and myeloid leukaemia risks were far from significant if using these techniques in the data analyses (Morfeld 2013).

Cole et al. (2010, supporting) analysed the epidemiological findings and the statistical methods used in the cohort study of Bean-Freeman et al. (2009) on industrial workers and in the case control study of Hauptmann et al. (2009) on embalmers. These 2 studies were pivotal for the Group 1 classification of IARC for leukemia. The authors concluded that neither study substantiated a significant excess of mortality from any lymphohematopoetic cancer although both were interpreted as positive for an association between formaldehyde and myeloid leukemia. In industrial workers there was only a weak and transitory relationship with peak exposure and for embalmers the limited exposure response relationship was not analysed for statistical significance. It is concluded that these 2 studies do not provide clear evidence between formaldehyde exposure and myeloid leukemia.

Rhomberg et al. (2011, supporting) used a hypothesis-based weight-of-evidence approach to assess the overall evidence for the formation of leukemia in humans after inhalation exposure to formaldehyde.They used the database from studies in humans, animals and mechanistic approaches and concluded that the case for a causal association is weak and strains biological plausibility. To their interpretation the association between formaldehyde exposure and leukemia in some human studies is rather due to chance or confounding.

Checkoway et al (2012, supporting) reviewed and summarised the total published epidemiological literature during 1966–2012. The literature was categorised according to study design and population: industrial cohort studies, professional cohort studies and population-based case-control studies. It was found that findings from occupational cohort and population-based case-control studies were very inconsistent for lympho-haematopoietic malignancies, including myeloid leukaemia. Apart from some isolated exceptions, relative risks were close to one, and there was little evidence for dose-response relations for any of the lympho-haematopoietic malignancies. It was concluded that at present, there is no consistent or strong epidemiologic evidence that FA is causally related to any lympho-haematopoietic malignancy. The absence of established toxicological mechanisms was found to further weaken the arguments for causation.

Checkoway et al. (2015, supporting) evaluated the association between cumulative and peak formaldehyde exposure and mortality from acute myeloid leukemia and other lymphohematopoetic malignancies observed in the NCI cohort (Beane-Freeman et al., 2009). When using the Cox proportional hazards analyses, acute myeloid leukemia was unrelated to cumulative exposure while for chronic myeloid leukemia a suggestive association with peak exposure was observed, albeit based on very small numbers. For Hodgkin lymphoma relative risk estimates were increased in the highest cumulative and peak exposure categories. No other lymphohematopoetic malignancy was related to chronic or peak exposure. It was concluded that this reanalysis does not support formaldehyde as a cause for acute myeloid leukemia. As no prior epidemiological evidence exists for Hodgkin leukemia and chronic myeloid leukemia, any causal interpretation for these malignancies was considered at most tentative.

Conclusion

1) A statistically increased risk for nasopharyngeal cancer in workers exposed to formaldehyde has only been detected at one out of ten plants in one cohort study but not in others. The validity and robustness of this specific observation is unclear as it suffers from small numbers of cases and an incomplete mortality follow-up.

2) A non-significant correlation between formaldehyde exposure and leukaemia, especially myeloid leukaemia was seen in some studies but not all. This tumour type is considered to be biologically not plausible taking into account all information from animal and human data in a weight of evidence approach.

A summary and evaluation of data on carcinogenicity available up to 2009 is reported in reviews of the IARC working group (IARC, 2006; 2012; Baan et al., 2009); details on epidemiological data are presented in Section 7.10.2 and carcinogenicity in experimental animals in Section 7.7 of the technical dossier.

Justification for classification or non-classification

The studies from 2009 up to 2015 did not strengthen an association between formaldehyde exposure and NPC or leukemia.

Although NPC is a rare tumor, specific dietary habit and smoking have been associated with the incidence rates of this tumor. In the updates of the 3 large cohort studies no strengthening indications have been obtained: in the NCI study only one additional NPC was identified, but this occurred in the lowest exposure category. No additional NPCs were observed in the UK cohort and in the NIOSH garment workers studies. In addition, two further epidemiological investigations did not identify an association with NPC: an Italian study comprised a smaller cohort of 2750 employees with 457 deaths and a study on 1.2 million empoyees from the Finnish Cancer Registry with 149 cases of NPC. Thus the former evidence, mainly from the NCI study, was not reinforced by the recent investigations.

In the updates of the 3 large cohort studies no further support for an association between formaldehyde and lymphohematopoetic neoplasms, especially for myeloid leukemias, were obtained. In the NCI study there was still a significant increase in some exposure categories, but the associations generally were weaker as compared to the former follow-up. The authors concluded that there was limited evidence for an association between formaldehde and leukemia. Similarly, in the NIOSH garment worker study an association with formaldehyde still prevailed, but theformer limited evidence was not strengthened by the update. In the UK cohort no significant associations with formaldehyde were seen for the different hematopoetic malignancies including a nested case-control study for all leukemias and myeloid leukemia. Also, the Italian study gave no indication in this respect. A metaanalysis focussing on high exposure groups reported an increased risk for leukemia, especially for myeloid leukemia. But this analysis suffered from methodological shortcomings by not using all available information. Some further analyse that included specifically the the recents studies of Beane-Freeman et al. (2009) and Hauptmann et al. (2009), that were pivotal for the Group 1 decision of IARC, concluded that the overall ecvidence for leukemia was at most weak and may be due to chance or confounding.

For other tumor types, no clear associations were seen for lung and pharyngeal cancer in epidemiological studies from 2011, 2012, and 2013.

RAC (2012) did not consider the epidemiological evidence as sufficient for a classification as a human carcinogen. RAC 2012 proposed the classification as Carc. Cat. 2; R45, according to Directive 67/548/EEC1999/45/ EC, and according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008, Annex VI, the classification isCarc. Cat 1B (H350).