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Carcinogenicity

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Description of key information

There are rat and mouse studies conducted by the US National Toxicology Program (NTP, 1986) on the carcinogenic effects of a C23(average) 43%Cl LCCP. These studies were conducted by gavage using very high doses, up to 5000 mg/kg/day.  Based on expert reviews of the strength and weight of available evidence, LCCPs are not expected to pose a carcinogenic hazard to humans.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

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Endpoint:
carcinogenicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1986
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
EPA OPP 83-2 (Carcinogenicity)
Principles of method if other than guideline:
US National Toxicology Program
GLP compliance:
yes
Specific details on test material used for the study:
Chlorinated Paraffins
Average Chain Length: C23
43% Chlorine by Weight
Molecular Weight 560 (average)
Species:
mouse
Strain:
B6C3F1
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Diet: ad libitum
- Water: ad libitum
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
No data
Analytical verification of doses or concentrations:
not specified
Details on analytical verification of doses or concentrations:
No data
Duration of treatment / exposure:
103 weeks
Frequency of treatment:
5 days/week
Post exposure period:
No data
Remarks:
Doses / Concentrations:
0, 2500, 5000 mg/kg body weight
Basis:

No. of animals per sex per dose:
50
Control animals:
yes, concurrent vehicle
Details on study design:
Dosing solutions were stored for no longer than 8 days.
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations checked included: signs of overt toxicity, morbidity and mortality.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Clinical signs were recorded weekly and palpation was started at week 41.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were recorded weekly for 13 weeks and then monthly.
Sacrifice and pathology:
GROSS PATHOLOGY: Yes, Each mouse received a post mortem examination, either on their death or at the termination of the study. Each mouse was subjected to a gross examination and a microscopic examination of a wide range of tissues (as specified).
Statistics:
Survival and tumour incidence data were subjected to statistical analyses by comparing the treated groups with the controls using a range of techniques. Tumour incidence in the treated groups was also compared with historical control data when there appeared to be a treatment related increase. Male: Historical incidence at study laboratory (mean +/- SD): 35/299 (12% +/- 5%); historical incidence in NTP studies: 132/1,097 (12% +/- 4%). Female: incidence at study laboratory (mean +/- SD): 18/300 (6% +/- 3%); historical incidence in NTP studies: 74/1092 (7% +/- 4%).
Clinical signs:
no effects observed
Mortality:
mortality observed, non-treatment-related
Description (incidence):
No significant differences in survival between dosed and vehicle control groups were observed. For female mice, 60%-70% of the early deaths in each group were attributed to utero-ovarian infection.
Body weight and weight changes:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Description (incidence and severity):
No significant nonneoplastic lesions were considered compound related in mice.
Description (incidence and severity):
The incidences of malignant lymphoma in male mice and hepatocellular carcinoma in female mice both showed a positive trend although only the incidence of malignant lymphoma in male mice exposed to 5000 mg/kg bw was statistically significant different from controls (Table 1).
Relevance of carcinogenic effects / potential:
Maligant lymphoma in male mice.
Dose descriptor:
NOAEL
Effect level:
> 5 000 mg/kg bw/day
Sex:
male/female
Remarks on result:
other: Effect type: toxicity (migrated information)
Dose descriptor:
NOAEL
Effect level:
> 5 000 mg/kg bw/day
Sex:
male/female
Remarks on result:
other: Effect type: carcinogenicity (migrated information)

Table 1. Incidence of malignant lymphoma in male mice and hepatocellular carcinoma in female mice.

Dose group(mg/kg/day)  0  2500  5000
Number males examined  50  50  50
Incidence of malignant lymphoma in males  6**  12  16*
Number females examined  50  49  50
Incidence of liver tumours in females      
Hepatocellular adenoma  3  2  7
Hepatocellular carcinoma  1**  1  6
Adenoma/carcinoma combined  4  3  10

* P < 0.05 relative to controls

** p< 0.05 increasing trend

There were no other treatment-related pathological lesions observed in either the male or female mice. The significance of the increased incidence of malignant lymphoma in male mice is unclear. Malignant lymphoma is a commonly occurring tumour in this strain of mouse and the effect was not seen in female mice. At most, the study shows equivocal evidence of carcinogenicity for this long-chain chlorinated paraffin in the mouse.

Conclusions:
An increased incidence of malignant lymphoma in male mice was reported at the highest dose tested, 5000 mg/kg/day.
Executive summary:

An increased incidence of malignant lymphoma in male mice was reported at the highest dose tested, 5000 mg/kg/day.

The significance of the increased incidence of malignant lymphoma in male mice is unclear. Malignant lymphoma is a commonly occurring tumour in this strain of mouse and the effect was not seen in female mice. Given the very high dose and the limited nature of the finding it appears the study shows just limited evidence of carcinogenicity for long-chain chlorinated paraffin in the mouse.

 

Overall, while there were some positive findings from this study, they occurred at an exposure level that is so high (5000 mg/kg/day) that the relevance of this property to a human health hazard assessment is doubtful.  IARC conclusion for LCCP is Class 3.

Endpoint:
carcinogenicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1982
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Deviations:
not specified
Principles of method if other than guideline:
US National Toxicology Program
GLP compliance:
yes
Specific details on test material used for the study:
Chlorinated Paraffins
Average Chain Length: C23
43% Chlorine by Weight
Molecular Weight 560 (average)
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Diet: ad libitum
- Water: ad libitum
Route of administration:
oral: gavage
Vehicle:
corn oil
Analytical verification of doses or concentrations:
yes
Duration of treatment / exposure:
103 weeks
Frequency of treatment:
5 days/week
Post exposure period:
No data
Remarks:
Doses / Concentrations:
male: 0, 1875, 3750 mg/kg body weight; female: 0, 100, 300, 900 mg/kg body weight
Basis:

No. of animals per sex per dose:
groups of 70 males/70 females.
Control animals:
yes, concurrent vehicle
Details on study design:
Initially, the test material was administered to groups of 70 male and 70 female Fischer 344 rats orally, by gavage, in corn oil. Control groups of 70 male and 70 female rats received corn oil alone. 10 rats from each group were terminated after 6 and 12 months respectively. The remaining 50 rats in each group were dosed for 103 weeks. Dosing solutions were stored for no longer than 8 days.
Positive control:
No data
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations checked included: signs of overt toxicity, morbidity and mortality.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Clinical signs were recorded weekly and palpation was started at week 41.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were recorded weekly for 13 weeks and then monthly.
Sacrifice and pathology:
GROSS PATHOLOGY: Yes, Each rat received a post mortem examination, either on their death or at the termination of the study. Each rat was subjected to a gross examination and a microscopic examination of a wide range of tissues (as specified).
Statistics:
Survival and tumour incidence data were subjected to statistical analyses by comparing the treated groups with the controls using a range of techniques. Tumour incidence in the treated groups was also compared with historical control data when there appeared to be a treatment related increase. Historical incidence of pheochromocytomas (all types) at study laboratory (mean +/- SD): 16/300 (5% +/- 3%); historical incidence in NTP studies: 65/1,093 (6% +/- 3%)
Clinical signs:
no effects observed
Mortality:
mortality observed, non-treatment-related
Description (incidence):
Survival of dosed and vehicle control rats was similar.
Body weight and weight changes:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
The primary nonneoplastic lesion associated with chlorinated paraffins (C23, 43% chlorine) administration was a diffuse lymphohistiocytic inflammation in the liver and in the pancreatic and mesenteric lymph nodes of male and female rats. Splenic congestion was a secondary effect. These lesions occurred in most animals of all treated groups, earlier and at lower doses in female rats than in male rats.
Description (incidence and severity):
The incidence of adrenal medullary phaeochromocytomas was increase in treated female rats compared to controls, although there was no evidence of hyperplasia. The increase was statistically significantly different in the group receiving 900 mg/kg bw (Table 1).
Relevance of carcinogenic effects / potential:
No significant findings of carcinogenic potential.
Dose descriptor:
LOAEL
Remarks:
noncancer
Effect level:
1 875 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male
Basis for effect level:
histopathology: non-neoplastic
Remarks on result:
other:
Remarks:
lowest dose tested
Dose descriptor:
LOAEL
Remarks:
noncancer
Effect level:
100 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
female
Basis for effect level:
histopathology: non-neoplastic
Remarks on result:
other:
Remarks:
lowest dose tested
Critical effects observed:
not specified

Table 1. Incidence of adrenal medullary hyperplasia and phaeochromocytomas in female rats.

 Dose group (mg/kg/day)  0  100  300  900
 Number examined  50  50  50  50
 Incidence of hyperplasia  6  3  1  6
 Incidence of phaeochromocytoma  1  4  6  7*

* p < 0.05

There were no other pathological lesions observed in either the female or male rats.

 

Conclusions:
Not anticipated to be carcinogenic. Non-carcinogenic effects were similar to other repeat-dose studies.

Additional information

There are rat and mouse studies conducted by the US National Toxicology Program (NTP, 1986) on the carcinogenic effects of a C23(average) 43%Cl LCCP. These studies were conducted by gavage using very high doses, up to 5000 mg/kg/day. Under the conditions of these 2-year gavage studies, NTP concluded there wasno evidence of carcinogenicity*of chlorinated paraffins (C23. 43% chlorine) for male F344/N rats given 1,875 or 3,750 mg/kg per day. There wasequivocal evidence of carcinogenicityof chlorinated paraffins (C23. 43% chlorine) for female F344/N rats as shown by an increased incidence of adrenal gland medullary pheochromocytomas. There wasclear evidence of carcinogenicityof chlorinated paraffins (C23, 43% chlorine) for male B6C3Fl mice as shown by an increase in the incidence of malignant lymphomas. There wasequivocal evidence of carcinogenicityof chlorinated paraffins (C23, 43% chlorine) for female B6C3F1 mice as shown by a marginal increase in the incidence of hepatocellular neoplasms.

In discussing whether the conclusion in male mice should remain clear evidence of carcinogenicity or be changed to some evidence of carcinogenicity, the NTP Science Advisory Board Technical Review Subcommitee members noted that malignant lymphoma is one of the more variable tumors and has a viral origin in many cases, and that statistically significant trends were obtained only if the lymphocytic and histiocytic tumor types were combined. The conclusion for male mice, clear evidence of carcinogenicity, was approved by five affirmative votes to four negative votes with two abstentions.

In contrast to these results, malignant lymphomas were not increased in similar NTP studies carried out on a mixture of shorter chain paraffins chlorinated to approximately 60% by weight (C12, 60% chlorine).

The NTP results and conclusions have been subjected to various reviews (IARC, 1990; NRC, 2000; UK EA, 2009, OECD SIDS, 2009, US EPA, 2013). These are summarized below.

 

IARC, 1990 concluded that the NTP studies provided limited evidence for the carcinogenicity of LCCP (C23, 43% chlorine), and did not assign a cancer classification for LCCPs.

 

The US National Research Council (NRC, 2000) reviewed the toxicological risks of selected flame retardant, including a LCCP (C24with 70 wt% Chlorine). It was concluded that: “LCCP are not likely to be a human carcinogen and derivation of a cancer potency factor is unnecessary.

 

The UK Environment Agency, 2009 concluded there is evidence that LCCPs are carcinogenic, but only at very high exposure levels. Because the chlorinated paraffins do not appear to have mutagenic potential it is likely that this carcinogenic activity is the result of a non-genotoxic mode of action and it can therefore be assumed that the carcinogenicity will have a threshold exposure level. Accordingly, a NOAEL of 2,500 mg/kg/day, at which the incidence of malignant lymphomas was similar to historical controls, can be identified.

 

The OECD SIDS Assessment, 2009 concluded that LCCPs present a low carcinogenic potential for humans.

 

Most recently, the US EPA, 2013 concluded that vLCCPs are not expected to pose a carcinogenic hazard to humans. In their review, US EPA commented:

“An increased incidence of malignant lymphoma in male mice was reported at the highest dose of

5,000 mglkg-bw/day when tested using a vLCCP (C23, 43 wt% Cl) in carcinogenicity studies in

male and female rats and mice. Malignant lymphoma is one of the more variable tumors in mice

and has a viral origin in many cases. In addition, data on the analogous short-chain chlorinated

paraffins ("SCCPs") have shown no increase in the incidence of malignant lymphoma in a carcinogenicity study of SCCPs. Therefore, EPA concludes that the increased incidence of

malignant lymphoma in male mice was not test-article related. Based on the foregoing

information, along with the lack ofin vitroandin vivogenotoxicity of vLCCPs, the Agency

concludes that vLCCPs are not expected to pose a carcinogenic hazard to humans.”

Finally, the dose at which the increased incidence of malignant lymphoma was observed in male mice by NTP was 5000 mg/kg/day. This is very high dose by current testing standards. Current OECD testing guidelines for chronic toxicity studies state that the top dose should not exceed 1000 mg/kg body weight/day (limit dose), except in cases when human exposure indicates the need for a higher dose level to be used.

References

IARC, 1990 IARC Monograph on the Evaluation of Carcinogenic Risks to Humans. Some Flame Retardants and Textile Chemicals, and Exposures in the Textile Manufacturing Industry. Volume 48. International Agency for Research on Cancer, Lyon, France, 1990.

 

NTP, 1986. Toxicology and carcinogenesis studies of chlorinated paraffins (C23, 43 percent chlorine) (Cas no. 633449-39-8) in F344/N rats and B6C3F1 (gavage studies). NTP Technical Report No. 305.

 

UK Environment Agency (EA, of England and Wales) (2009). Environmental Risk Evaluation Report: Long-Chain Chlorinated Paraffins. January 2009.

US EPA, 2013. EPA-HQ-OPPT-2013-0399-0012.

NRC, 2000. Toxicological Risks of Selected Flame-Retardant Chemicals. 

OECD SIDS Assessment Report,Long Chain Chlorinated Paraffins (LCCPs).October, 2009

Justification for classification or non-classification

Based upon the available data and expert reviews, no carcinogenicity classification is assigned to LCCPs. This decision is supported by various expert reviews of the strength and weight of available evidence. Key factors underlying the justification for no classification include the following: evidence of carcinogenicity is limited to increases in malignant lymphoma observed in a single sex of one species tested at an unusually high dose; malignant lymphoma is one of the more variable tumors in mice and has a viral origin in many cases; studies of analogous shorter chain chlorinated paraffins have not shown similar findings; a lack of in vitro and in vivo genotoxicity by LCCPs.