Formaldehyde

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Nov 8, 1984 to Nov 8, 1986

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Two-years drinking-water study of formaldehyde in rats

Author:

Til HP, Woutersen R, Feron V, Hollanders V, Falke H, Clary J

Year:

1989

Bibliographic source:

Fd Chem Toxic 27: 77-87

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1988

Report date:

1988

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Formaldehyde

EC Number:

200-001-8

EC Name:

Formaldehyde

Cas Number:

50-00-0

Molecular formula:

CH2O

IUPAC Name:

formaldehyde

Details on test material:

- Name of test material (as cited in study report): formaldehyde

Specific details on test material used for the study:

TEST MATERIAL
- Source: Celanese Chemicals, Dallas, TX, USA
- Lot/Batch number: UN2213
- Paraformaldehyde prills 95 % (plus 5 % water)

Test animals

Species:

rat

Strain:

Wistar

Remarks:

Cpb:WU, SPF

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: TNO Central institute for the breeding of laboratory animals, Zeist, the Netherlands
- Age at study initiation: 5 weeks old
- Weight at study initiation: 35 - 50 g
- Housing condition: 5 per cage, stainless-steel cages fitted with wire-mesh floor and front
- Diet: Institute's grain-based open-formula diet, ad libitum
- Water: drinking water, ad libitum
- Acclimatization period: 9 days

DETAILS OF FOOD AND WATER QUALITY
- The contaminants in basal diet and in drinking water are determined twice a year

ENVIRONMENTAL CONDITIONS
- Temperature: 20 - 24°C
- Humidity: 40 - 70 %
- Air changes: about 10 times per hour
- Photoperiod: 12 hours / 12 hours

Administration / exposure

Route of administration:

oral: drinking water

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS
The test substance was administered to the rats in the drinking-water (tap-water), to provide target intake levels of 5, 25 and 125 mg test substance/kg body weight/day. Fresh solutions were prepared every week and stored in closed plastic containers in a room kept at 15°C. The concentrations of the test substance in the solutions were adjusted weekly for the first 12 weeks of the study on the basis of the estimated mean body weight and liquid consumption for the next week. Such adjustments were made every 4 week from week 12 to 52, on the basis of the estimated mean body weight and liquid consumption for the forthcoming 4 weeks. After week 52, the concentrations were kept constant, because of the considerable decrease in liquid consumption in the top-dose rats due to their rejection of the test solution. The concentrations of the test substance present in the various experimental solutions at the time of consumption were calculated to be on average 20, 260 or 1900 mg/L for the low-, mid- and high-dose groups, respectively.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The determination of formaldehyde in drinking water was conducted by iodometric titration according to Van der Linden and Visser (1968).

Duration of treatment / exposure:

24 months (interim sacrifice after 12 or 18 months)

Frequency of treatment:

daily, 7 days each week

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

5 mg/kg bw/day (nominal)

Remarks:

1.2 mg/kg bw/day measured dose levels in males (mean)
1.8 mg/kg bw/day measured dose levels in females (mean)

Doses / concentrations 2

Dose / conc.:

25 mg/kg bw/day (nominal)

Remarks:

15 mg/kg bw/day measured dose levels in males (mean)
21 mg/kg bw/day measured dose levels in females (mean)

Doses / concentrations 3

Dose / conc.:

125 mg/kg bw/day (nominal)

Remarks:

82 mg/kg bw/day measured dose levels in males (mean)
109 mg/kg bw/day measured dose levels in females (mean)

No. of animals per sex per dose:

70, 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

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS
- Time schedule: daily

CLINICAL OBSERVATIONS
- Time schedule: daily

BODY WEIGHT
- Time schedule: at the start of the study, weekly in the first 12 weeks, once every 4 weeks thereafter

FOOD CONSUMPTION
- Time schedule: weekly in the first 12 weeks, 2week periods every 3 months thereafter

WATER CONSUMPTION AND COMPOUND INTAKE
- Time schedule: weekly periods throughout the study
- Compound intake was calculated on the basis of intended levels of the test substance it the solutions, and liquid intake and body weight figures as measured in the corresponding weeks and after correction for the stability of diluted test substance solutions

OPHTHALMOSCOPIC EXAMINATION
- Cornea, conjunctivae, sclera, iris and fundus oculi
- Were made in all rats of the control and top-dose groups prior to the administration of the test substance and in week 52 end 103
- Eye examinations were carried out using a hand slit lamp after induction of medriasis by a 1 %solution of atropine sulphate

HAEMATOLOGY AND CLINICAL CHEMISTRY
- Blood samples were collected from the tail tips of ten rats/sex/group in week 26 and 103 and were examined for haemoglobin concentrations, packed cell volume and erythrocyte, leucocyte and thrombocyte counts
- Whole blood taken from ten rats/sex/group after overnight fasting in week 27, 52, 78 and 104 was examined for glucose
- Orbital blood samples taken from ten rats/sex/group in week 28 and abdominal blood samples taken from ten rats/sex/group in week 53, 79 and 105 were centrifuged at 1250 g for 15 min and then analyzed by conventional methods for alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, total protein, albumin, total bilirubin, urea, creatinine, cholesterol, y-glutamyl transferase and calcium, inorganic phosphate, chloride, sodium and potassium

URINALYSIS
- In week 27, 52, 78 and 104, ten rats/sex/group were deprived of water for 24 hour and of food for 16 hour
- Urine was collected during the last 16 hour of the deprivation period and its volume and density were determined
- In pooled urine samples collected in week 27 and 104 semi-quantitative observations of protein, glucose, occult blood, ketones, urobilinogen and bilirubin were made and the sediment was examined by microscopy
- pH determinations were carried out in week 27, 52, 78 and 104 in freshly voided 3-hour urine samples

Sacrifice and pathology:

Before the start of the study, two subsets each of 10 male and 10 female rats and one of 50 rats of each sex were defined in each group. The survivors of the first (10 rats/sex/group), second (10 rats/sex/group) and third (50 rats/sex/group) subsets were killed in week 53, 79 and 105, respectively. The rats were killed by exsanguination from the abdominal aorta, whilst under light ether anaesthesia, and a thorough autopsy was performed. The following organs of each rat were weighed and the organ to body weight ratios were calculated: adrenals, brain, heart, kidneys, liver, ovaries, pituitary, spleen, testes and thyroid. Samples of these organs and of the skin, skeletal muscle, mammary glands (females), Harderian and exorbital lachrymal glands, nose, lungs, aorta, parotid, submandibular and sublingual salivary glands, oesophagus, forestomach, glandular stomach, small and large intestine, pancreas, urinary bladder, epididymides, prostate, uterus, stemum, mesenteric and axillary lymph nodes, spinal cord, sciatic nerve and eyes were fixed in 10% neutral buffered formalin, embedded in paraffin wax, sectioned at 5 μm, and stained with haematoxylin and eosin. Detailed microscopic examinations were carried out on all mentioned organs of all rats of the control and the high-dose groups. The liver. lungs, stomach and nose of all rats of the low- and mid-dose groups were also examined. In addition, we examined the adrenals, kidneys, spleen, testes, thyroid, ovaries, pituitary and mammary glands (females) of the rats of subset three (killed in wk 105) of the low- and mid-dose groups. A thorough autopsy was also performed on rats that were found dead or were killed when moribund during the study. The organs of these animals were not weighed, but tissues were preserved if autolysis was not too advanced.

Statistics:

Data on body weight were evaluated by a one-way analysis of covariance, followed by Dunnett's multiple comparison tests. The laboratory determinations and organ weights were evaluated by a one-way analysis of variance, followed by Dunnett's multiple comparison tests, except for the differential white blood cell counts, which were analyzed by the Mann-Whitney U-test. Data on food and liquid intake were evaluated by analysis of variance, followed by least significant difference tests (experimental unit: the cage). The mortality incidences and the histopathological changes were examined by Fisher's exact probability test (two-sided).

Results and discussion

Results of examinations

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

No overt signs of toxicity due to the administration of the test substance were observed. The behaviour of the rats during the first year of the study was unremarkable. After 12 months, ageing symptoms developed in all groups and the number of unthrifty rats increased. The incidence of partly closed eyes was more frequently observed in the top-dose rats than in the rats of the other groups, including the controls. The incidences of all the other phenomena observed were about equally distributed among the groups; there were no consistent differences between groups in time of appearance of clinical signs. In general the animals remained in good health. Of the 12- and 18-month interim kill grossly visible or palpable masses were observed in a few rats only, without evidence of a relationship with the treatment. In the 24-month study grossly visible or palpable masses occurred frequently in all groups. In females of the top-dose group, both the total number of masses and the number of animals bearing masses was slightly higher than in controls, however, the differences were not statistically significant.
An incidental finding was the slight yellowing of the fur in the mid- and top-dose rats from week 3 - 6. The yellow colour was more intense on the back and flanks than on the belly and cheeks of the animals. The individual hairs were coloured from the skin till the top of the hair. The colour intensified to canary yellow in the course of the next 10 - 12 weeks and then did not change much in intensity. In the mid-dose rats the phenomenon was much less pronounced than in the top-dose rats. The low-dose rats did not show any yellow discolouration.

Mortality:

mortality observed, treatment-related

Description (incidence):

From the mortality data it appears that up to week 72 mortality was very low in both sexes. Thereafter, mortality gradually increased. Mortality rate was statistically significantly increased in males of the mid-dose group at the end of the study (p < 0.05), but increased mortality was not observed in the top-dose group. In females there were no significant differences in mortality amnong the groups. After 24 months mortality for males and females of the control group was 25 and 31 %, respectively.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean body weights of the top-dose males were statistically significantly decreased throughout the study. Mean body weights of the females of this group were invariably bower than those of the controls; the 5 differences reached the level of statistically significance only in week 1, 24 to 40 and 76 to 104.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Food intake of the top-dose males was statistically significantly diminished. In females of this group a similar effect was observed, but it was less pronounced. The differences with the controls reached the level of significance only incidentically.

Food efficiency:

effects observed, treatment-related

Description (incidence and severity):

Food conversion efficiency of the top-dose males calculated over the period of rapid growth (week 0 to 12) was generally lower than in controls, the differences being statistically significant in wneek 1, 7 and 10 (p < 0.001). In females no treatment-related differences in food conversion efficiency were observed amongst groups.

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

Liquid intake showed a considerable decrease in the top-dose group in both sexes. The mid-dose group consumed slightly less liquid than did the controls, but the differences were generally not statistically significant. In the last week of the study there was a significant decrease in liquid intake in males of the low- and mid-dose groups. We have no explanation for this irregularity.

Ophthalmological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Ophthalmoscopic examination, carried out prior to the start of the study and week 52 and 103, did not reveal any difference between test rats and controls that suggested an effect of the test substance.

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

Haematology did not show statistically significant differences among the various groups in week 26. In week 103 packed cell volume was decreased in the top-dose females (p < 0.05), but this phenomenon was not associated with significant changes in other red blood cell parameters and therefore, no toxicological significance was attached to this finding. White blood cell counts in week 103 were relatively low in all test groups in males, the differences with the controls being statistically significant in the mid- and top-dose groups (p < 0.05). However, there was no evidence of a dose-related response. In the top-dose females the percentage of neutrophils was increased and that of the lymphocytes decreased (p < 0.05).

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

In week 27/28 plasma alkaline phosphatase activity and total plasma protein content were slightly decreased at the mid- and top-dose level in both sexes; the differences with the controls were not always statistically significant in the mid-dose group. Total plasma protein content was also slightly decreased in the top-dose males in week 78/79. Plasma urea content was slightly increased in the top-dose males in week 27/28 only. In week 78/79 plasma cholesterol levels were slightly, though statistically significantly decreased in the mid- and top-dose groups in males. There was, however, no evidence of a dose-related response. Plasma potassium concentration was statistically significantly increased in females of the top-dose group. Clinical chemistry values -including the above mentioned parameters obtained in week 52/53 and 103/104 did not show statistically significant differences among the various groups. Therefore, no toxicological significance is attached to the slight changes seen in week
26/27 and 78/79.

Endocrine findings:

not examined

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

A statistically significant increase in density of the urine, accompanied by a tendency towards lower urine production was observed in the top-dose group in males in week 27 and 52 and in females in week 27. Mean urinary pH was increased in males of the low- and mid-dose group in week 27 and 78 and decreased in females of the top-dose group in week 27 and 78. The occurrence of occult blood in the urine was increased in all test groups in males in week 27 and in the mid- and top-dose group in females in week 104. However, there was no evidence of a dose-related response. Therefore, no toxicological significance was attached to this finding. There were no changes of any significance in the composition of the urine with respect to appearance, protein, glucose, ketones, urobilinogen, bilirubin or microscopy of the sediment either in week 27 or 104 .

Behaviour (functional findings):

no effects observed

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

The absolute weights of the heart and liver were statistically significantly decreased in males of the top-dose group in week 79 and 105, while testes and kidney weight were decreased in top-dose males in week 79 and 105, respectively. The decreases are most probably the result of the lower body weights in this group. Absolute organ weights of the rats killed after one year did not show statistically significant differences among the various groups. The relative weight of the kidneys in females was increased in the top-dose group at all stages, the differences with the controls being statistically significant only in week 53 and 105. The relative weight of the brain was statistically significantly increased in the top-dose group in males at all stages and in females in week 105. Relative testes weight was increased in the top-dose group in week 105 only. These increases in relative brain and testes weights are ascribed to the lower body weights of the rats in this group and the well-known inverse correlation between body weight and 1relative brain and testes weights.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

FIRST SUBSET (rats found dead, killed in extremis or killed in week 53)
Gross examination at autopsy revealed treatment-related changes in the stomach of both males and females. These changes comprised: i) a raised or thickened limiting ridge in one female of the low-dose group, in several mid-dose rats and in most top-dose animals. The severity of this alteration was positively correlated with the test substance level. ii) nodular thickenings and irregular areas of the mucosa of the fundus (glandular stomach) in one female of the bow-dose group and in a few animals of the mid- and top-dose groups.

SECOND SUBSET (rats found dead, killed in extremis or killed in week 79)
Gross examination at autopsy of the rats killed in week 79 revealed treatment-related abnormalities in the stomach only. The limiting ridge of the forestomach was raised and thickened in most animals of the top-dose group. Two females of the mid-dose group and one of the bow-dose group also showed slight thickening of the limiting ridge. In addition, slight surface irregularities in the glandular stomach were seen in 3 male and 6 female top-dose rats as well as in one female control animal. All other gross changes observed were about equally distributed among the various groups or occurred only in a single animal. Three female animals of this subset ware found dead or were killed in extremis before week 79. One control female bad a large polyp in the uterus and one female mid-dose rat bad a large tumour of the pituitary. The cause of death of the third animal (a mid-dose female) could not be established at autopsy.

THIRD SUBSET (rats found dead, killed in extremis or killed in week 105)
Gross examination at autopsy of the rats of the main study revealed treatment-related changes in the stomach only. The limiting ridge of the forestomach was raised and thickened in most male (36/50) and female (43/50) rats of the top-dose group. A few animals, both males and females, of the other groups, controls included, showed the same phenomenon. In addition, several animals of the top-dose group exhibited surface lesions in the forestomach (8 males and 6 females) and/or a strickingly smooth appearance of the glandular stomach (4 males and 13 females). Occasionally, the same changes were found in animals of the other
groups, controls included. The number of male top-dose rats showing gross signs of nephropathy (discolouration and irregular surface of the kidneys frequently accompanied by enlarged parathyroids) was significantly lower than the number of controls showing these lesions. Moreover, the number of male rats with atrophic testes was also remarkably low in the top-dose group as compared to controls (3 in the top-dose group versus 12 in the controls). The incidence of some other gross changes such as ovarian cysts, pituitary tumorous mass, hydrothorax and spotted appearance of the lungs varied considerably among the groups. Since, however, a distinct dose-response relationship was absent and large variations in incidence of these age-associated lesions are not uncommon, these differences are not considered to be related to treatment.

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

FIRST SUBSET (rats found dead, killed in extremis or killed in week 53)
Treatment-related changes were found only in the stomach of top-dose animals. The changes included papillary epithelial hyperplasia in the forestomach and focal atrophic gastritis occasionally accompanied by ulceration of the fundic mucosa. The hyperplasia in the forestomach was seen as a thickenend layer of keratinized stratified squamous epithelium which was mainly found on the limiting ridge or in the vicinity of the limiting ridge. Cellular or nuclear atypia was not observed. In the glandular stomach focal atrophic gastritis occasionally accompanied by mucosal ulceration occurred to a varying degree in each of the top-dose males and females. In the affected areas the mucosa was reduced in width compared to an unaffected mucosa, and the lesions had bulky borders. Occasionally, bulky plugs of necrotic tissue, inflammatory exudate, mucus and feed particles were seen to be attached to the damaged mucosa. The inflammatory process was generally restricted to the lamina propria but in some cases involved the entire mucosa. In a few animals the defect in the wall was seen to extend to the muscularis mucosae and was diagnosed as ulceration. In one top-dose female a focus of glandular hyperplasia was present in affected mucosa. "Blinded" histopathological review of the stomach slides of all animals of the low- and mid-dose rats did not demonstrate microscopic changes even not in the additional sections of the rats with grossly visible mucosal alterations. lt is well-known from previous studies performed in our Institute that a thickened limiting ridge, which is clearly visible at gross examination is not always recognizable as such upon microscopic examination. The nodular irregularities grossly seen in the fundic mucosa of several rats of the mid-dose group and of one female of the low-dose group most probably represent aggregates of mucus and feed particles attached to the mucosa and formed as a result of fixation by the test substance. These aggregates may have disappeared during processing of the organ or may not be recognizable as such upon microscopy. However, in several top-dose rats such plugs of mucus and feed particles indeed were visible upon microscopy but in these cases they also contained inflammatory exudate and necrotic material; in addition in these animals the plugs were seen to be attached to the damaged mucosa. All other non-neoplastic histopathological changes obser-ved were commnon findings in rats of this age and strain or they occurred in one or a few animals and are therefore not considered to be treatrnent-related.

SECOND SUBSET (rats found dead, killed in extremis or killed in week 79)
Treatment-related changes were found only in the stomach of top-dose animals. The changes included focal hyperkeratosis of the forestomach epithelium and chronic atrophic gastritis of the glandular stomach. Focal ulceration in the forestomach or glandular stomach was observed in two male top-dose rats. The histopathological changes observed in the forestomach ware mainly seen as papillary epithelial hyperplasia frequently accompanied by hyperkeratosis located on the limiting ridge or in the vicinity of the limiting ridge. Frequently the mucosa showed an irregular layer of hyperplastic basal cells. Occasionally, similar changes but to a minimal degree ware observed in one or two animals of the other groups, controls included. In the glandular stomach chronic atrophic gastritis occurred to a varying degree in each of the top-dose animals. In the affected areas the mucosa was reduced in width compared to the unaffected mucosa, and the lesions had bulky borders. Occasionally, bulky plugs of necrotic tissue, inflammatory exudate, mucus and feed particles were seen to be attached to the damaged mucosa. The inflammatory process, characterized by infiltrations of lymphocytes and macrophages (or mononuclear cells) and fibrosis was restricted to the lamina propria but in some cases involved the entire mucosa. When the defect in the wall was seen to extend to the muscularis mucosae, the lesion was diagnosed as ulceration. The slight thickening of the limiting ridge seen in 3 female rats of the lower dose groups was not seen at microscopy. This phenomenon is not unexpected since it is well-known from previous studies performed in our Institute that a thickened limiting ridge, which is easily recognizable at gross examination is not always found as such upon microscopical examination. All other non-neoplastic histopathological changes observed were common findings in rats of this age and strain or they occurred in one or a few animals and are therefore not considered to be treatment-related.

THIRD SUBSET (rats found dead, killed in extremis or killed in week 105)
Microscopical examination of rats in the main study revealed test substance-related gastric and renal changes in animals of the top-dose group only. In the forestomach, an increased degree and/or incidence of the following histopathological changes were seen in the top-dose group: (i) Papillary epithelial hyperplasia frequently acconipanied by hyperkeratosis, and ii) Focal ulceration. Hyperkeratosis of a remarkably folded, slightly hyperplastic layer of keratinized stratified squamous epithelium was mainly seen on the limiting ridge or in the vicinity of the limiting ridge. Frequently, the mucosa showed an irregular layer of hyperplastic basal cells. An ulcer of the forestomach was found in 8 male and 5 female rats of the top-dose group; it invariably occurred near the limiting ridge.
Similar histopathological changes were occasionally seen in rats of the other groups, controls included and are known to occur in rats due to stress (e.g. starvation). They are not uncommon in historical control animals. In the glandular stomach the following compound-related changes were observed: chronic atrophic gastritis, in several animals accompanied by ulceration and/or glandular hyperplasia. Chronic atrophic gastritis occurred to a varying degree in each of the top-dose animals, except for one male rat. In the affected areas the mucosa was reduced in width as compared to the unaffected mucosa, and the lesions demonstrated bulky borders. In some cases the inflammatory process involved the entire mucosa arid was seen to extend to the whole muscularis mucosae meeting the criteria for the diagnosis ulceration. The incidence and/or degree of renal papillary necrosis was higher in males and females of the top-dose group than in the other groups, controls included. This renal change was seen as an early interstitial lesion located in the tip of the papilla. lt was characterized by patchy necrosis of interstitial cells, capillaries and loops of Henle, and in more severe cases the necrotic papilla appears as a rather homogeneous eosinophilic structure with ghost-like remnants of the normal architecture. Remarkably, nephrosis was less severe in males of the top-dose group than in males of the other groups. In females, however, the incidence of nephrosis was slightly higher in the test groups than in the controls, but a dose-response relationship was absent. The decrease in severity of nephrosis in males of the top-dose group was accompanied by a decrease in both the incidence of (bilateral) glandular hyperplasia of the parathyroids and the incidence of periarteritis in the testes. This relationship is not unexpected since these histopathological changes are all part of the well-known nephrotic syndrome in rats. The incidence of several other histopathological changes varied considerably among the various groups, but in no case a consistent or relevant relationship with doses was observed. Thus, there were no indications that the incidence or severity of any of these lesions was influenced by the exposure to the test substance. Moreover, the changes observed are age-associated and a considerable variation in their incidence and severity is not uncommon in rats of the strain used.

Histopathological findings: neoplastic:

effects observed, treatment-related

Description (incidence and severity):

FIRST SUBSET (rats found dead, killed in extremis or killed in week 53)
The following neoplastic lesions were observed in various groups: one fibroadenoma of the mammary glands, one haemorrhagic tumour of the pituitary gland, one mesenchymoma in the skin and two fibroznatous polyps in the uterus. Except for the mesenchymoma all tumours are commnon findings in the strain of rats used. The mesenchymoma found in a male top-dose animal is an uncommon finding; it is considered to be a fortuitous observation unrelated to the test compound.

SECOND SUBSET (rats found dead, killed in extremis or killed in week 79)
The following neoplastic lesions ware observed: 3 fibroadenomas of the mammary glands (all females; 2 controls and 1 top-dose rat); 1 fibroadenoma in the skin of a male control animal; 6 tumours of the pituitary gland (1 mid-dose male; 1 control, 1 low-dose and 3 top-dose females); 1 adenoma in the thyroid of a male control rat; 5 polyps in the uterus (2 controls, 2 low-dose and 1 mid-dose animal); 1 mesenchymal tumour (male mid-dose rat) and 1 lipoma (male low-dose rat) in the abdominal cavity. The tumours observed are common findings in the strain of rats used and moreover there was no indication that the incidence had been influenced by the test compound. Therefore, these tumours were not ascribed to the ingestion of the test substance.

THIRD SUBSET (rats found dead, killed in extremis or killed in week 105)
Apart from 2 (benign) papillomas, one in a male of the low-dose group and one in a female control rat, gastric tumours were not observed. All tumours are common neoplasms in the strain of rats used. In males of the top-dose group the total number of tumourous and the number of tumour-bearing rats were lower than in controls. Although differences in their incidence occurred between the groups, there was no indication that these differences ware related to the exposure to the test substance. They are considered to be related to normal ageing or to represent incidental findings without any toxicological significance.

Effect levels

Dose descriptor:

NOAEL

Effect level:

25 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

gross pathology

haematology

organ weights and organ / body weight ratios

urinalysis

water consumption and compound intake

Remarks on result:

other: actual doses: males 15 mg/kg, females 21 mg/kg

Target system / organ toxicity

Critical effects observed:

yes

Lowest effective dose / conc.:

82 mg/kg bw/day (actual dose received)

System:

gastrointestinal tract

Organ:

stomach

Treatment related:

yes

Dose response relationship:

yes

Relevant for humans:

yes

Applicant's summary and conclusion

Conclusions:

NOAEL = 15 mg/kg bw/day

Executive summary:

In a reliable GLP-conform study similar to OECD TG 453, a combined chronic toxicity/carcinogenicity study, 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.

Oral exposure via the drinking water induced 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.