ε-caprolactam

Carcinogenicity

Description of key information

Based on the results of studies similar to OECD TG 451, the NOAEL for carcinogenicity was determined to be >375 mg/kg bw/d in rats and > 2143 mg/kg bw/d in mice.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report): Caprolactam
- Analytical purity: purity and identity analyses performed at Midwest Research Institute were consistent with the structure and literature values. Results from thin-layer and vapor-phase chromatography indicated a single homogeneous compound.
- Lot/batch No.: DB 7-7-75 from Dow Badische Company

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: NCI Frederick Cancer Research Center
- Age at study initiation: 3 weeks old
- Mean weight at study initiation: male 18 g, female 16 g
- Housing: 5 per cage
- Diet (e.g. ad libitum): Purina Lab Chow and required amount of Caprolactam
- Water (e.g. ad libitum): Tap water
- Acclimation period: 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22-26
- Humidity (%): 30-70
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: feed

Details on exposure:

DIET PREPARATION
- Test diets were formulated by mixing Purina Lab Chow and the required amount of Caprolactam in a Patterson-Kelly twin-shell blender for 20 minutes.
- Storage temperature of food: 4°C for no longer than 2 weeks

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

103 weeks

Frequency of treatment:

daily

Post exposure period:

2 weeks

Remarks:

Doses / Concentrations:
7500 and 15000 ppm
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
Ca. 1071 and 2143 mg/kg bw
Basis:
other: calculated based on a conversion factor of 7 (Derelanko, M.J., The Toxicologist's Pocket Handbook. 2nd Ed., p 29, 2008)

No. of animals per sex per dose:

50

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale:
A subchronic study was conducted to determine the concentrations to be used in the chronic 2-year cancer study (see 7.5.1 for details).
Diets containing 0, 5000, 10000, 15000, 20000 or 30000 ppm test substance were fed for 13 weeks to groups of 10 male and 10 female mice. Clinical observations were made twice daily and animals were weighed weekly. At the end of the 13-weeks study survivors were killed, necropsies were performed on all animals, and tissues were taken fore histopathologic analysis. Two of the ten female mice that received 30000 ppm diet and one female that received 20000 ppm died as a result of an accident. No deaths occurred among male mice. A depression in mean body weight gain was observed in all dosed mice, but mean body weight gain was no different for male mice fed 30000 ppm (36%) than for those fed 5000 ppm. Weight gain depression for females was dose related. No compound-related histopathologic effects were observed. Based on deaths and decreased mean weight gain, doses selected for the chronic studies in mice were 7500 and 15000 ppm test substance in feed.

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily


BODY WEIGHT: Yes
- Time schedule for examinations: every 2 weeks for the first 13 weeks and monthly thereafter


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Tissue masses were recorded.

HISTOPATHOLOGY: Yes. The following tissues and organs were examined microscopically: abnormal lymph nodes, skin, mandibular lymph nodes, mammary gland, salivary gland, thigh muscle, sciatic nerve, bone marrow, costochondral junction (rib), thymus, larynx, trachea, lungs and bronchi, heart, thyroid, parathyroid, esophagus, stomach, duodenum, jejunum, ileum, colon, mesenteric lymph nodes, liver, gallbladder, pancreas, spleen, kidneys, adrenals, bladder, seminal vesicles/prostate/testes or ovaries/uterus, nasal tissues, brain, pituitary, eyes, and spinal cord. Special staining techniques were utilized as necessary.

Statistics:

Method of Cox (1972) for testing two groups for equality and Tarone's (1975) extensions of Cox's methods for testing for a dose-related trend.
One-tailed P values have been reported except the departure from linearity test, which is reported only when its two-tailed P value is less than 0 .05.

Clinical signs:

no effects observed

Description (incidence and severity):

No compound-related clinical signs were reported.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

No compound-related mortalities were reported. In the males survival at termination of the experiment was 40/50 (80%) in the control group, 48/50 (96%) in the low dose group, and 43/50 (86%) in the high-dose group.
In the females, survival at termination was 38/50 (76%) of the controls, 41/50 (82%) of the low-dose group, and 46/50 (92%) of the high-dose group.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Throughout the study, mean body weights of dosed rats of either sex were lower than those of controls, and the decrements in mean body weight gain were dose related. The decrease in body weight in the high dose group was up to 14% in males and 12% in females. The decrease in lower dose group was below 10%.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

No effect on food consumption was observed.

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Description (incidence and severity):

No compound-related alterations were observed.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

No compound-related alterations were observed.

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

A variety of neaplasms occurred in both the control and dosed mice, but no increased incidences of any types of neoplasms were seen in dosed mice. The observed neoplasms were typical of those seen in this strain of mouse.
A treatment-related effect can therefore not be identified.

Other effects:

not specified

Dose descriptor:

NOAEL

Effect level:

> 2 143 mg/kg bw/day (actual dose received)

Sex:

male/female

Basis for effect level:

other: no effects in highest dose level

Dose descriptor:

NOAEL

Effect level:

ca. 1 071 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: decrease in bw

Conclusions:

The NOAEL for carcinogenicity was found to be > 2143 mg/kg bw/d.

Executive summary:

A subchronic study was conducted to determine the concentrations to be used in the chronic 2-year cancer study. Diets containing 0, 5000, 10000, 15000, 20000 or 30000 ppm test substance were fed for 13 weeks to groups of 10 male and 10 female mice. Clinical observations were made twice daily and animals were weighed weekly. At the end of the 13-weeks study survivors were killed, necropsies were performed on all animals, and tissues were taken fore histopathologic analysis. Two of the ten female mice that received 30000 ppm diet and one female that received 20000 ppm died as a result of an accident. No deaths occurred among male mice. A depression in mean body weight gain was observed in all dosed mice, but mean body weight gain was no different for male mice fed 30000 ppm (36%) than for those fed 5000 ppm. Weight gain depression for females was dose related. No compound-related histopathologic effects were observed. Based on deaths and decreased mean weight gain, doses selected for the chronic studies in mice were 7500 and 15000 ppm test substance in feed.

No evidence of neoplastic or non-neoplastic lesions associated with oral administration of the test substance was demonstrated by histopathologic examination. Based on the results, the NOAEL for carcinogenicity was found to be > 2143 mg/kg bw/d.

Reference 2

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

GLP compliance:

not specified

Specific details on test material used for the study:

- Name of test material (as cited in study report): Caprolactam
- Analytical purity: purity and identity analyses performed at Midwest Research Institute were consistent with the structure and literature values. Results from thin-layer and vapor-phase chromatography indicated a single homogeneous compound.
- Lot/batch No.: DB 7-7-75 from Dow Badische Company

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: NCI Frederick Cancer Research Center
- Age at study initiation: 3 weeks old
- Mean weight at study initiation: male 100 g, female 90 g
- Housing: 4 per cage
- Diet (e.g. ad libitum): Purina Lab Chow and required amount of Caprolactam
- Water (e.g. ad libitum): Tap water
- Acclimation period: 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22-26
- Humidity (%): 30-70
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: feed

Details on exposure:

DIET PREPARATION
- Test diets were formulated by mixing Purina Lab Chow and the required amount of Caprolactam in a Patterson-Kelly twin-shell blender for 20 minutes.
- Storage temperature of food: 4°C for no longer than 2 weeks

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

103 weeks

Frequency of treatment:

daily

Post exposure period:

2 weeks

Remarks:

Doses / Concentrations:
3750 and 7500 ppm
Basis:
nominal in diet

Remarks:

Doses / Concentrations:
Ca. 187.5 and 375 mg/kg bw
Basis:
other: calculated based on a conversion factor of 20 (Derelanko, M.J., The Toxicologist's Pocket Handbook. 2nd Ed., p 29, 2008)

No. of animals per sex per dose:

50

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale:
A subchronic study was conducted to determine the concentrations to be used in the chronic 2-year cancer study (for details see 7.5.1). in brief, diets containing 0, 625, 1250, 2500 or 7500 ppm test substance were fed for 13 weeks to groups of 12 male and 12 female rats. Clinical observations were made twice daily and animals were weighed weekly. At the end of the 91-days, study survivors were killed, necropsies were performed on all animals, and tissues were taken for histopathologic analysis. Observed weight gain depression (12% or less for males and 14% or less for females) was not dose related. Food consumption compared with controls was decreased by 23% and 19% for males and females of thr high dose group (7500 ppm), respectively. No compound-related histopathologic effects were observed. Based on decreased mean weight gain, doses selected for the chronic studies in rats were 3750 and 7500 ppm test substance in feed.

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily


BODY WEIGHT: Yes
- Time schedule for examinations: every 2 weeks for the first 13 weeks and monthly thereafter


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes.
Tissue masses were recorded.

HISTOPATHOLOGY: Yes.
The following tissues and organs were examined microscopically: abnormal lymph nodes, skin, mandibular lymph nodes, mammary gland, salivary gland, thigh muscle, sciatic nerve, bone marrow, costochondral junction (rib), thymus, larynx, trachea, lungs and bronchi, heart, thyroid, parathyroid, esophagus, stomach, duodenum, jejunum, ileum, colon, mesenteric lymph nodes, liver, pancreas, spleen, kidneys, adrenals, bladder, seminal vesicles/prostate/testes or ovaries/uterus, nasal tissues, brain, pituitary, eyes, and spinal cord. Special staining techniques were utilized as necessary.

Statistics:

Method of Cox (1972) for testing two groups for equality and Tarone's (1975) extensions of Cox's methods for testing for a dose-related trend.
One-tailed P values have been reported except the departure from linearity test, which is reported only when its two-tailed P value is less than 0 .05.

Clinical signs:

no effects observed

Description (incidence and severity):

No compound-related clinical signs were reported.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

No compound-related mortalities were reported. In the males survival at termination of the experiment was 32/50 (64%) in the control group, 33/50 (66%) in the low dose group, and 37/50 (74%) in the high-dose group.
In the females, survival at termination was 40/50 (80%) in the controls, 42/50 (84%) in the low-dose group, and 38/50 (76%) in the high-dose group.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Throughout the study, mean body weights of dosed rats of both genders were lower than those of controls. The decrements in mean body weight gain were dose related. The decrease in body weight in the high dose group was upto 20% in males and 14% in females. The decrease in lower dose group was below 10%.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Feed consumption was inversely related to dose. Feed consumption by high-dose rats of either sex was only 70%-80% that of the controls.

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Description (incidence and severity):

No compound-related alterations were observed.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

No compound-related alterations were observed.

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

The various types of neoplasm occurring in dosed and control rats were not related to the chemical administration.
In all exposed groups including the control, high rates of interstitial-cell tumors were observed in testes (84% control, 86% low dose, 96% high dose). Although this tumor commonly occurred in historical control groups at levels above 80% , a treatment-related effect can therefore not be identified.

Other effects:

not specified

Dose descriptor:

NOAEL

Effect level:

> 375 mg/kg bw/day (actual dose received)

Sex:

male/female

Basis for effect level:

other: no effect in highest dose tested

Dose descriptor:

NOAEL

Effect level:

ca. 187.5 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: decrease in body weight

Conclusions:

The NOAEL for carcinogenicity was determined to be >375 mg/kg bw/d.

Executive summary:

A subchronic study was conducted to determine the concentrations to be used in the chronic 2-year cancer study. in brief, diets containing 0, 625, 1250, 2500 or 7500 ppm test substance were fed for 13 weeks to groups of 12 male and 12 female rats. Clinical observations were made twice daily and animals were weighed weekly. At the end of the 91-days, study survivors were killed, necropsies were performed on all animals, and tissues were taken for histopathologic analysis. Observed weight gain depression (12% or less for males and 14% or less for females) was not dose related. Food consumption compared with controls was decreased by 23% and 19% for males and females of thr high dose group (7500 ppm), respectively. No compound-related histopathologic effects were observed. Based on decreased mean weight gain, doses selected for the chronic studies in rats were 3750 and 7500 ppm test substance in feed.

No evidence of neoplastic or non-neoplastic lesions associated with oral administration of the test substance was demonstrated by histopathologic examination. This is indicating that the test substance was not carcinogenic to F344 rats under the conditions of this bioassay. The NOAEL for carcinogenicity was determined to be >375 mg/kg bw/d.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

375 mg/kg bw/day

Study duration:

chronic

Species:

rat

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

The test substance is not warranted for classification and labelling according to Directive 67/548/EEC Annex I and

according to the EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.

Additional information

The test substance was tested for its carcinogenic potential in 2 species (rats and mice; NTP, 1982).

50 male and 50 female Fischer-344 rats per dose group were fed diets containing 187.5 mg/kg bw and 375 mg/kg bw test substance for 103 weeks. A dietary control group was also included.

Similarly B6C3F1 mice were fed with 2143 mg/kg bw and 1071 mg/kg bw test substance for 103 weeks. Survival in both species was similar to that of controls. The various types of neoplasms occurring in dosed groups and control group in both species were comparable and did not appear to be related to the test substance administration.

Summarized, no carcinogenic potential was detected by feeding maximal dose levels of 187.5 mg/kg bw to rats or 2143 mg/kg bw to mice. Besides a decrease in body weight gain no further signs of systemic toxicity were observed.

Inconsistent results were reported in various cell transformation assays.

In one cell transformation assay the test substance failed to transform Hamster Embryo cells at dose levels up to 10000 µg/ml (ACC, 1979).

In an interlaboratory comparison treatment of Syrian hamster embryo (SHE) cells with the test substance dose levels up to 1000 µg/ml resulted in consistently higher transformation rates compared to non-treated control cells (Jones et al., 1988).

However, in a second interlaboratory comparison, results were negative with SHE cells at doses of 1-1000 µg/ml (LeBoeuf et al., 1989). In both interlaboratory validations significant cyotoxicity was observed with and above 1000 µg/ml. An apparent variance between both was the use of a slightly lower pH value by LeBoeuf et al., resulting in higher transformation efficiencies. Furthermore in this assay known carcinogens were consistently positive and non-carcinogens consistently negative, assigning a certain level of reliability to the test design chosen.

In a weight of evidence approach no indications for a carcinogenic potential can be deduced from these cell transformation assays and based on the 2-years carcinocenicity bioassays, the test substance does not require any classification according to EU and GHS standards.