Zinc methacrylate

Carcinogenicity

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Reference 1

Endpoint:

carcinogenicity: inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Study period:

28 January 1981 - 24 January 1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Justification for type of information:

Please refer to section 13 of the dataset for read across justification.

Reason / purpose for cross-reference:

read-across source

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Portage, MI)
- Age at study initiation: 7-8 weeks
- Housing: Animals were housed individually in stainless steel wire cages (Lab Products, Inc., Rochelle Park, NJ)
- Diet: NIH 07 Rat and Mouse Ration (Zeigler Bros., Inc., Gardners, PA and Wayne LAB BLOX), ad libitum except during exposure
- Water: Automatic watering system (Edstrom Industries, Waterford, WI), ad libitum
- Acclimation period: 22 days

ENVIRONMENTAL CONDITIONS
- Temperature: 72-79 °F
- Humidity: 45-65 %
- Air changes: 20 room air changes/hour
- Photoperiod: 12 h dark / 12 h light

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

Methyl methacrylate was pumped from a stainless steel reservoir to a vaporizer by a stable micrometering pump with adjustable drift-free pump rates. The vaporizer was heated to 50 ± 2 °C, and the study material vapor, along with an air stream, entered the test chamber. The uniformity of the vapor concentration in the exposure chambers was measured periodically throughout the studies.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Methyl methacrylate concentrations were monitored on-line twice during each exposure hour, initially by a photoionization detector and later by gas chromatographic analysis.
Results: Mean daily concentrations were within 2 % of the target concentrations.

Duration of treatment / exposure:

2 years (102 weeks)

Frequency of treatment:

6 h/day, 5 days/week

Post exposure period:

Not applicable

Remarks:

Doses / Concentrations:
0, 500 and 1000 ppm (males) and 0, 250 and 500 ppm (females)
Basis:
other: analytically confirmed nominal concentrations

No. of animals per sex per dose:

50

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale: Doses were selected based on the results of 14- week study. Because of the deaths, incidences of lesions of the nasal turbinates and brain, and weight gain depression at higher concentrations, the concentrations selected for rats for the 2-year studies were 500 and 1000 ppm for males and 250 and 500 ppm for females.

Positive control:

No

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed twice daily, and clinical signs were recorded once per week.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Individual clinical examinations were made at weighing.

BODY WEIGHT: Yes
- Time schedule for examinations: Once per week for the first 13 weeks of the study and once per month thereafter.

FOOD CONSUMPTION, FOOD EFFICIENCY AND WATER CONSUMPTION: No data

HAEMATOLOGY, CLINICAL CHEMISTRY, URINALYSIS, NEUROBEHAVIOURAL EXAMINATION: No data

Sacrifice and pathology:

GROSS PATHOLOGY AND HISTOPATHOLOGY: Yes
- Animals found moribund and those surviving to the end of the studies were humanely killed. A necropsy was performed on all animals including those found dead, unless they were excessively autolyzed or cannibalized, missexed, or found missing.
- During necropsy, all organs and tissues were examined for grossly visible lesions. Tissues were preserved in 10 % neutral buffered formalin, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. Three separate sections of the nasal turbinates were examined. One section was made at the level just caudal to the incisor teeth, the second section was midway between the incisors and first molar, and the third section was at the middle of the second molar.
- Necropsy and histologic examination performed on all animals; the following tissues were examined: gross lesions and tissue masses, regional lymph nodes, mandibular lymph node, sternebrae including marrow, thyroid gland, parathyroids, small intestine, rectum, colon, liver, mammary gland, prostate/testes/epididymis or ovaries/uterus, lungs and mainstem bronchi, nasal cavity and turbinates, skin, heart, esophagus, stomach, salivary gland, brain, thymus, trachea, pancreas, spleen, kidneys, adrenal glands, urinary bladder, pituitary gland, preputial or clitoral gland, and tracheobronchial lymph nodes.

Other examinations:

None

Statistics:

- Survival: Statistical analyses for possible dose-related effects on survival used Cox’s (1972) method for testing two groups for equality and Tarone’s (1975) life table test to identify dose-related trends.
- Neoplasm and nonneoplastic lesion incidences: Incidental tumor analysis, life table test (Cox, 1972; Tarone, 1975), Fisher exact test and the Cochran-Armitage trend test (Armitage, 1971; Gart et al., 1979) were used to assess neoplasm and nonneoplastic lesion prevalence.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

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

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

MORTALITY
- No significant differences in survival were observed between any groups of either sex.

BODY WEIGHT AND WEIGHT GAIN
- Mean body weights of 1000-ppm male rats were 5-10 % lower than those of the controls after Week 81. Mean body weights of 500-ppm female rats were 6-11 % lower than those of the controls after Week 73.

HISTOPATHOLOGY: NON-NEOPLASTIC
- No histopathological findings other than local findings in the respiratory tract. Systemic histopathological effects, as for example in the brain in females particularly at 2000 ppm and above in the subchronic range finding study (Batelle, 1980), are absent in this 104 week study.
- Nasal cavity and Olfactory sensory epithelium: Serous and suppurative inflammation and degeneration of the olfactory epithelium in the nasal cavity were observed at increased incidences in exposed male and female rats relative to controls. Serous inflammation was characterized by noncellular mucus in the lumen of the posterior region of the nasal cavity. Suppurative inflammation was characterized by an infiltration of neutrophils and varying numbers of mononuclear cells into the mucosa and submucosa of the nasal turbinates and wall of the nasal cavity. Degeneration of the olfactory epithelium was characterized by a loss of sensory neuroepithelial cells from the epithelium (atrophy) and, in the most severely affected areas, replacement by respiratory epithelium (metaplasia). This degeneration was accompanied by variable atrophy of the nerve bundles in the submucosa.
- Lung: Alveolar macrophages were observed at increased incidences in exposed male and female rats. The severity in all groups was considered minimal. Focal or multifocal fibrosis was observed at an increased incidence in 500-ppm female rats.

HISTOPATHOLOGY: NEOPLASTIC
- There was no treatment-related increase in tumour incidence.
- Hematopoietic System: There were no differences in the character of the mononuclear cell leukemia found in the dosed female rats and the controls. The incidences of mononuclear cell leukemia in the three groups of male rats were not statistically different by life table analysis.
- Pituitary Gland: Pituitary gland adenomas or carcinomas (combined) in male rats occurred with a significant negative trend, and the incidence in the 1000 ppm group was significantly lower than that in the controls. The incidences of pituitary gland adenomas in the three groups of female rats were not different statistically.
- Preputial Gland: Preputial gland adenomas and carcinomas occurred in male rats with a significant negative trend, and the incidence in the high dose group was significantly lower than that in the controls.

Key result

Dose descriptor:

LOAEC

Effect level:

ca. 250 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Histopathology (irritation)

Key result

Dose descriptor:

NOAEC

Effect level:

ca. 500 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Gross pathology and histopathology (organ effects)

Key result

Dose descriptor:

NOAEC

Effect level:

ca. 1 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No effects up to the highest dose

None

Conclusions:

Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for rats; whereas the NOAEC for systemic effects and LOAEC for local effects (nasal irritation) were 500 ppm and 250 ppm, respectively.

Executive summary:

In a carcinogenicity study performed similarly to OECD Guideline 451, read across substance Methyl methacrylate was administered via inhalation (whole body exposure) to groups of Fischer 344 rats (50/sex/dose) at the concentrations of 0, 500 and 1000 ppm (males) and 0, 250 and 500 ppm (females) for 102 weeks (6 h/day, 5 days/week). All animals were observed twice daily, and clinical signs were recorded once per week and bodyweights were recorded once per week for the first 13 weeks and once per month thereafter. Necropsy and histopathological examination performed on all animals at the end of study. No significant differences in survival were observed between any groups of either sex. Male and female rat body weights were lower at the 1000 ppm (5-10%) and 500 ppm (6-11%) exposure levels, respectively, presumably due to reduced food consumption due to nasal irritation and damage of olfactory epithelium. While food consumption was not recorded in this study this association is confirmed by two other studies, the developmental toxicity study with Methyl methacrylate with reduced food consumption and reduced body weight gain at concentrations higher than 99 ppm (Solomon, 1993) and a subchronic inhalation study with methacrylic acid where there was also an association of irritative effects in the nose and reduced food consumption and reduced body weight gain (BASF, 2008). Consequently, reduced body weight gain, while clearly treatment-related is considered to be secondary to the local effects in the nose and not the result of true systemic toxicity. The primary finding was inflammation of rat nasal cavity as well as olfactory epithelial degeneration at all exposure levels in male and female rats. In contrast to the 90 d range finding study with histopathological changes in females at exposures of 1000 ppm and above (Battelle, 1980), no other significant histopathological changes were reported in male and female rats after 104-week exposures to Methyl methacrylate vapour in this study. There was no treatment-related increase in tumour incidence. Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for rats; whereas the NOAEC for systemic effects and LOAEC for local effects (nasal irritation) were 500 ppm and 250 ppm, respectively (Chan, 1986). Similar results can be expected for zinc dimethacrylate.

Reference 2

Endpoint:

carcinogenicity: inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Study period:

28 January 1981 - 24 January 1983

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Remarks:

NTP standard protocol, cancer bioassay with limited dose range

Justification for type of information:

Please refer to section 13 of the dataset for read across justification.

Reason / purpose for cross-reference:

read-across source

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 451 (Carcinogenicity Studies)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

no

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories (Portage, MI)
- Age at study initiation: 8-9 weeks
- Weight at study initiation: males 151-155 g; females 117-119 g (mean weights per treatment group)
- Housing: individually
- Acclimation period: 3 weeks

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

Methyl methacrylate was pumped from a stainless steel reservoir to a vaporizer by a stable micrometering pump with adjustable drift-free pump rates. The vaporizer was heated to 50 ± 2 °C, and the study material vapor, along with an air stream, entered the test chamber. The uniformity of the vapor concentration in the exposure chambers was measured periodically throughout the studies.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Methyl methacrylate concentrations were monitored on-line twice during each exposure hour, initially by a photoionization detector and later by gas chromatographic analysis.
Results: Mean daily concentrations were within 2 % of the target concentrations.

Duration of treatment / exposure:

2 years (102 weeks)

Frequency of treatment:

6 h/day, 5 days/week

Post exposure period:

Not applicable

Remarks:

Doses / Concentrations:
0, 500 and 1000 ppm (corresponding to 2.05 and 4.1 mg/L)
Basis:
other: analytically confirmed nominal concentrations

No. of animals per sex per dose:

50

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale: Doses were selected based on the results of 14-week study.

Positive control:

No

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed twice daily, and clinical signs were recorded once per week.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Individual clinical examinations were made at weighing.

BODY WEIGHT: Yes
- Time schedule for examinations: Once per week for the first 13 weeks of the study and once per month thereafter.

FOOD CONSUMPTION, FOOD EFFICIENCY AND WATER CONSUMPTION: No data

HAEMATOLOGY, CLINICAL CHEMISTRY, URINALYSIS, NEUROBEHAVIOURAL EXAMINATION: No data

Sacrifice and pathology:

GROSS PATHOLOGY AND HISTOPATHOLOGY: Yes
- Animals found moribund and those surviving to the end of the studies were humanely killed. A necropsy was performed on all animals including those found dead, unless they were excessively autolyzed or cannibalized, missexed, or found missing.
- During necropsy, all organs and tissues were examined for grossly visible lesions. Tissues were preserved in 10 % neutral buffered formalin, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. Three separate sections of the nasal turbinates were examined. One section was made at the level just caudal to the incisor teeth, the second section was midway between the incisors and first molar, and the third section was at the middle of the second molar.
- Necropsy and histologic examination performed on all animals; the following tissues were examined: gross lesions and tissue masses, regional lymph nodes, mandibular lymph node, sternebrae including marrow, thyroid gland, parathyroids, small intestine, rectum, colon, liver, mammary gland, prostate/testes/epididymis or ovaries/uterus, lungs and mainstem bronchi, nasal cavity and turbinates, skin, heart, esophagus, stomach, salivary gland, brain, thymus, trachea, pancreas, spleen, kidneys, adrenal glands, urinary bladder, pituitary gland, preputial or clitoral gland, and tracheobronchial lymph nodes.

Other examinations:

None

Statistics:

- Survival: Statistical analyses for possible dose-related effects on survival used Cox’s (1972) method for testing two groups for equality and Tarone’s (1975) life table test to identify dose-related trends.
- Neoplasm and nonneoplastic lesion incidences: Incidental tumor analysis, life table test (Cox, 1972; Tarone, 1975), Fisher exact test and the Cochran-Armitage trend test (Armitage, 1971; Gart et al., 1979) were used to assess neoplasm and nonneoplastic lesion prevalence.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

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

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

MORTALITY
- No significant differences in survival were observed between any groups of either sex.

BODY WEIGHT AND WEIGHT GAIN
Mean body weights of both male and female mice at both concentrations were lower than those of the controls throughout most of the study (males: up to 16% lower mean body weight; females: up to 17%).

HISTOPATHOLOGY: NON-NEOPLASTIC
Acute and chronic inflammation, epithelial hyperplasia, cytoplasmic inclusions in the epithelial cells, and degeneration of the olfactory epithelium in the nasal cavity occurred at increased incidences in male and female mice exposed to the test substance. Accumulation of homogeneous, eosinophilic material in the cytoplasm of cells, primarily of the respiratory epithelium (cytoplasmic inclusions) was significantly increased in treated animals when compared to that of the controls.
Uterine adenocarcinomas were reduced in animals from both of the treatment groups, but statistical significance was not observed.
In the lungs, interstitial inflammation was increased in the male mice from the high-group, while alveolar/bronchiolar adenomas and alveolar/bronchiolar adenomas and carcinomas (combined) were significantly reduced in the male mice exposed to 500 and 1000 pp

A NOAEC could not be established based on nasal lesions. No significant differences of the survival rates were observed between any groups. No treatment-related tumors were observed.

Key result

Dose descriptor:

LOAEC

Remarks:

for local effects in the URT

Effect level:

ca. 500 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: inflammation, epithelial hyperplasia, cytoplasmic inclusions in the epithelial cells, and degeneration of the olfactory epithelium in the nasal cavity

Key result

Dose descriptor:

NOAEC

Remarks:

for systemic effects

Effect level:

ca. 1 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no biologically relevant adverse systemic effects observed

Key result

Dose descriptor:

NOAEC

Remarks:

for systemic effects

Effect level:

ca. 1 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No effects up to the highest dose

None

Conclusions:

Under the study conditions, there was no evidence of carcinogenic activity of Methyl methacrylate for mice; whereas the NOAEC for systemic and LOAEC for local effects (nasal irritation) were 500 ppm and 250 ppm, respectively. Similar results can be expected for zinc dimethacrylate.

Executive summary:

In a carcinogenicity study performed similarly to OECD Guideline 451, read across substance Methyl methacrylate was administered via inhalation (whole body exposure) to groups of mice (50/sex/dose) at the concentrations of 0, 500 and 1000 ppm for 102 weeks (6 h/day, 5 days/week). All animals were observed twice daily, and clinical signs were recorded once per week and bodyweights were recorded once per week for the first 13 weeks and once per month thereafter. Necropsy and histopathological examination performed on all animals at the end of study. Mean body weights of both male and female mice at both concentrations were lower than those of the controls throughout most of the study (males: up to 16% lower mean body weight; females: up to 17%). Acute and chronic inflammation, epithelial hyperplasia, cytoplasmic inclusions in the epithelial cells, and degeneration of the olfactory epithelium in the nasal cavity occurred at increased incidences in male and female mice exposed to the test substance. Accumulation of homogeneous, eosinophilic material in the cytoplasm of cells, primarily of the respiratory epithelium (cytoplasmic inclusions) was significantly increased in treated animals when compared to that of the controls. Uterine adenocarcinomas were reduced in animals from both of the treatment groups, but statistical significance was not observed. In the lungs, interstitial inflammation was increased in the male mice from the high-group, while alveolar/bronchiolar adenomas and alveolar/bronchiolar adenomas and carcinomas (combined) were significantly reduced in the male mice exposed to 500 and 1000 ppm. Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for mice; whereas the NOAEC for systemic and LOAEC for local effects (nasal irritation) were 500 ppm and 250 ppm, respectively (Chan, 1986). Similar results can be expected for zinc dimethacrylate.

Reference 3

Endpoint:

carcinogenicity: inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Justification for type of information:

Please refer to section 13 of the dataset for read across justification.

Reason / purpose for cross-reference:

read-across source

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

no

Principles of method if other than guideline:

Not applicable

GLP compliance:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

Three hundred male and 300 female rats were received form Charles River Breeding Laboratories, Inc. (Wilmington, MA, USA). Animals were maintained under quarantine for 19 days, during such time all rats were evaluated for clinical signs of disease and an ophthalmoscopic examination. Following the quarantine period, 70 males and 70 females were assigned to each of the four exposure groups (including the control). The animals were housed by sex in wire mesh cages (seven/cage). Animals were provided feed and water ad libitum, except during the exposure period.

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

Animals were exposed to the test substance vapor in 6000 L inhalation chambers under dynamic conditions of 1000 L/minute of air flow. The control animals were exposed to filtered room air in a chamber with similar air-flow characteristics.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Concentrations of the test substance in each chamber were measured hourly during each exposure period using an infrared analyzer.

Duration of treatment / exposure:

2 years (104 weeks)

Frequency of treatment:

6 h/day, 5 days/week

Post exposure period:

Not applicable

Remarks:

Doses / Concentrations:
25, 100 and 400 ppm (corresponding to 0.10, 0.41 and 164 mg/L, respectively)
Basis:
other: analytically confirmed nominal concentrations

No. of animals per sex per dose:

70

Control animals:

yes, concurrent no treatment

Details on study design:

None

Positive control:

No

Observations and examinations performed and frequency:

All animals were observed for mortality and morbidity daily. Individual body weight data were collected at the start of the study, weekly for the first twelve weeks and biweekly to week 24, every fourth week to week 78 and biweekly until study termination (week 104). At such time, a more detailed evaluation of gross toxicity and tissue masses was performed. Ophthalmoscopic evaluations were conducted at weeks 13, 52 and 102.

Sacrifice and pathology:

Blood samples were collected from 10 males and 10 females per dose group at weeks 13, 52 and 104 and 10 males and 10 females in the control and the high-dose group at weeks 26 and 78. The following hematological parameters were evaluated at each sampling interval: hematocrit, hemoglobin, red blood cells counts, erythrocyte counts, total white blood cell counts, erythrocyte morphology and prothrombin time. Bone marrow samples were collected from the femurs of all rats killed at week 13 and 52 and from 10 males and 10 females from each group at study termination. Blood also was obtained from the abdominal aorta of all rats killed at week 13, 52 and study termination. The following clinical chemistry parameters were evaluated: glucose, blood urea nitrogen, serum glutamic-pyruvic transaminase, alkaline phosphatase, total protein, total albumin, total cholesterol (except for week 13) and triglycerides (except for week 13). Twenty-four hour urine samples were collected from 10 animals per sex per group at weeks 13, 52 and 104. The following parameters were evaluated: appearance, pH, specific gravity, glucose, ketones, total protein, bilirubin, and occult blood. Necropsy: Ten rats per sex per group were sacrificed after 13 and 52 weeks of exposure. The remaining animals were sacrificed after 104 - 106 weeks of exposure. Necropsies were performed on all decedents. The brain, kidneys, lungs spleen, adrenal and thyroid glands and the testis or ovaries were weighed and the organ to body weight ratios were calculated. The following tissues were preserved in buffered 10% formalin: brain, pituitary, spinal cord, esophagus, salivary glands, thyroid glands with parathyroid, lings, mediastinal lymph nodes, thymus, heart, aorta, larynx, spleen, kidneys, adrenals, stomach, duodenum, ileum, jejunum, colon, skin, mesenteric lymph nodes, urinary bladder, uterus, mammary gland, prostate, seminal vesicles, costochondral junction, liver, sciatic nerve, skeletal muscle, pancreas, nasal cavity and gross lesions. The eyes from all rats and the testes with epididymides were preserved in Bouin's fixative. Microscopic evaluations were made using the tissue listed above in the control and the high-dose groups at study termination. The brain, spinal cord, pituitary, thyroid, adrenal, heart, lung, liver, spleen, kidney, and ovaries/testes from 10 animals per sex in the low- and mid-dose groups and the nasal cavities from all animals in the low- and mid-dose groups were evaluated microscopically. Sections from the adrenals, testes or ovaries, heart, kidneys, pituitary, thyroids, liver, nasal cavities and lungs of control and high-dose animals were examined microscopically after the week 13 and 52 interim sacrifices. Following the issuance of the original report, tissue blocks of the nasal cavities from the animals killed at the terminal sacrifice and the control and high-dose dose group at week 13, were obtained and a composite cross-sectional map of representative nasal cavity lesions with the approximate distribution was prepared for the mid- and high-dose groups.

Other examinations:

None

Statistics:

Pair-wise comparisons of the mean body weights were performed. Clinical laboratory data, with the exception of urinalysis and leukocyte differentials, terminal body weights and absolute and relative organ weights of all animals killed at weeks 13 and 52 and at study termination were subjected to a preliminary test for the equality of variance. To evaluate tumor incidence, Fisher's one-sided exact test was conducted between the control and high-dose groups. For all analyses, statistical significance was determined by a p value < 0.05.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not examined

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

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

The mean analytical concentrations of the test substance in the exposure chambers were 25.0, 99.8 and 396.1 ppm less than 10% per dose level.

Mortality rates for the treated animals were similar to those of the controls. No signs of treatment-related toxicity were observed. At the 13, 52 and 104-week observation intervals, cloudy eyes and bloody crusts around one or both eyes were noted in all of the treatment groups, as well as the control animals. Body weights for males were lower than the control at various intervals but overall were considered equivalent over the 104-week period. Mean body weights for females were lower than the controls at ca. 1.64 mg/L (400 ppm) after week 52. Hematology, clinical chemistry and urinalyses did not indicate any treatment-related effects in any of the parameters evaluated.

Gross necropsy of the rats sacrificed at weeks 13 and 52 did not show any treatment-related effects.

The following information was obtained from the reevaluation of the nasal tissues from this study originally conducted by Reno et al. (1979) - see also summary for this study in this Dossier. Microscopic evaluation of the of the nasal cavity sections obtained from the animals exposed to the test substance for 13 weeks showed degeneration of the neuroepithelial cell lining of the dorsal meatus in conjunction with atrophy of Bowman's glands and focal basal cell hyperplasia. Lesions were identified on the tips of the maxilloturbinates and nasoturbinates and focally along the nasal septum in the more anterior regions of the nose. These lesions were characterized by chronic

active inflammation, respiratory epithelial hyperplasia and squamous metaplasia. No microscopic findings were identified in the ocular tissue or the lungs or other tissues. Blocks of the nasal cavities of animals from the 52-week sacrifice were unable to be located and, therefore, were not evaluated. No new findings were identified in the tissues that were available for animals exposed to the test substance for 52 weeks. Spontaneous disease lesions included early respiratory disease in both the control animals and the animals exposed to 400 ppm of the test substance. Also focal areas of pneumonitis were observed in two females in the control group. Gross necropsy after

two years of exposure to the test substance showed no treatment-related effects. The nasal cavity was the target organ for chronic toxicity. Rats exposed to the 0.41 and 1.64 mg/L (100 and 400 ppm) dose group had dose-dependant lesions in the anterior portions of the nasal cavity. The olfactory epithelium lining the dorsal meatus in the anterior region of the nasal cavity was affected by exposure to higher concentrations of the test substance. The microscopic changes consisted of degeneration of the olfactory epithelium and underlying Bowman's glands, hyperplasia of basal cells, replacement of olfactory epithelium by ciliated epithelium and inflammation of the mucosa and/or submucosa. Lesions tended to be bilateral in distribution. The olfactory lesions in rats exposed to ca. 0.41 mg/L (100 ppm) were localized in the more posterior (level 3) portion of the dorsal meatus, while those in animals exposed to 400 ppm were found in levels 2 and 3. Hyperplasia of glands in the lamina propria and/or goblet cells and inflammation of the mucosa/lamina propria were observed in the respiratory epithelium in the high exposure group animals. No effects were seen in nasal epithelium of rats exposed to 25 ppm Methyl methacrylate. No statistically significant differences were observed in the frequency of tumors between the rats exposed to ca. 1.64 mg/L (400 ppm) of the test substance and that of the controls. In female rats exposed to ca. 1.64 mg/L (400 ppm) of the test substance, a statistically significant decrease in pituitary adenoma/carcinomas and mammary gland fibroadenomas was recorded. In male rats, a decreased incidence of pheochromocytoma was observed.

Key result

Dose descriptor:

NOAEC

Effect level:

ca. 400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No increase in tumour incidence up to the highest concentration tested

None

Conclusions:

Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for rats; whereas the NOAEC for systemic and LOAEC for local effects (nasal irritation) were considered as 400 ppm and 100 ppm, respectively. Similar results can be expected for zinc dimethacrylate.

Executive summary:

In a combined chronic toxicity/carcinogenicity study in F344 rats, 70 male and 70 female F344 rats were exposed to vapor concentrations of 0, 25, 100 or 400 ppm read across substance methyl methacrylate for two years. Ten male and ten female rats from all groups were sacrificed after 13 and 52 weeks of exposure and all surviving rats were killed during week 104-106. Histological examination was conducted on more than 35 tissues including 3-4 cross-sections of the nasal cavity. Tissues from the trachea and the pharynx/larynx were not preserved for histopathologic examination. Mortality rates of treatment and control groups did not show significant differences. No compound-induced clinical signs were observed. After week 52, mean body weight of high dose females was generally lower than controls gaining intermittently significance. Reduced growth represented the only adverse effect outside the respiratory tract. Evaluation of hematology, clinical chemistry and urinalysis data did not reveal any methyl methacrylate associated effect. At the end of the study, there were weight changes of some organs in males or females without any consistent relationship to the treatment. Similarly, no treatment-related macroscopic findings were observed in any of the dose groups. No histomorphological lesions other than nasal lesions were attributable to methyl methacrylate exposure of any exposed group. The examination of nasal cavities from male and female rats exposed to 400 ppm for 13 weeks or 52 weeks revealed a degeneration of the neuroepithelial olfactory cells lining the dorsal meatus of the anterior portions of the nasal cavities in conjunction with atrophy of Bowman’s glands and focal basal cell hyperplasia. Chronic active inflammation, respiratory epithelial hyperplasia and squamous metaplasia characterized the lesions on the tips of the maxilloturbinate and nasoturbinats and focally along the nasal septum in more anterior regions of the nose. At the final sacrifice, nasal lesions were evident in males and females of the 100 ppm and 400 ppm exposure groups characterised by inflammatory degeneration of nasal epithelium (Lomax, 1997). Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for rats; whereas the NOAEC for systemic and LOAEC for local effects (nasal irritation) were considered as 400 ppm and 100 ppm, respectively. Similar results can be expected for zinc dimethacrylate.

Reference 4

Endpoint:

carcinogenicity: oral

Type of information:

read-across from supporting substance (structural analogue or surrogate)

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

Justification for type of information:

Please refer to section 13 of the dataset for read across justification.

Reason / purpose for cross-reference:

read-across source

Qualifier:

no guideline followed

Principles of method if other than guideline:

Chronic, repeated dose study with exposure via drinking water.

GLP compliance:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: "young" (unspecified)
- Weight at study initiation: Male: 63 g; Female: 60 g
- Housing: Animals were individually housed
- Diet: Food (finely ground Purina Dog Chow Kibbled Meal, ad libitum
- Water: Drinking water, ad libitum

Route of administration:

oral: drinking water

Vehicle:

unchanged (no vehicle)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples were analyzed polarographically for monomer content. It is apparent that there was a maximal loss of 15 % of the methyl methacrylate within 72 h.

Duration of treatment / exposure:

104 weeks (2 years)

Frequency of treatment:

Daily, ad libitum

Remarks:

Doses / Concentrations: 6, 60 and 2000 ppm at the start of the study; raised after 5 months to 7, 70 and 2000 ppm (limited by palatability)
Basis:

No. of animals per sex per dose:

25

Control animals:

yes, concurrent no treatment

Details on study design:

- Twenty-five male and female albino (Wistar) rats were administered 6, 60 or 2000 ppm of methyl methacrylate in the drinking water. The concentrations of the low- and mid-dose groups were increased to 7 and 70 ppm at the beginning of the fifth month of the study.
- Stock solutions of the monomers were prepared in tightly stoppered carboys once a week and the drinking bottles were filled twice a week, water remaining in the bottles at refilling being discarded. Rats quickly learn to drink from these bottles. Dripping does not occur unless the cage or bottle is jarred; evaporation loss averages 5 mL in 72 h at 72 °C.
- Prior to the start of the study, it was apparent that methyl methacrylate was volatilizing at the tip of the water bottles. A special design was employed to reduce the volatilization and measurements showed that the methyl methacrylate concentrations remained within 15% of nominal for 72 h.
- The low and medium concentrations in the water were selected with the expectation that the diet equivalents would approximate 10 and 100 ppm. The high concentration was selected following preliminary tests that indicated that this level would significantly depress fluid consumption.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: Body weights were measured prior to study initiation, at weeks 1, 3, 6, 13, 26, 52, 78 and 104.

FOOD AND WATER CONSUMPTION:
- Food and water consumption was measured over a three day period at the end of one and four weeks, monthly through month six and during even months thereafter.

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- How many animals: Five rats/sex/dose at three month intervals
- Parameters checked: Hematocrit, hemoglobin, total white and differential white cell counts

CLINICAL CHEMISTRY: No

URINALYSIS: Yes
- Semiquantitative tests for urinary concentrations of reducing substances and protein were performed on urines pooled from 5 rats/sex/group at three month intervals.

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes; At two years, survivors were sacrificed and organ to body weight measurements were made for heart, spleen, kidney, liver and testes. Tissues preserved from all animals on study included heart, lung, kidney, liver, urinary bladder, spleen, gastroenteric, skeletal muscle, bone marrow, skin, brain, thyroid, adrenal, pancreas, pituitary and gonad.
HISTOPATHOLOGY: Yes; Histopathology was conducted on all tissues collected except from animals in the low dose group.

Other examinations:

None

Statistics:

No data

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

no effects observed

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

effects observed, treatment-related

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

not examined

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

MORTALITY
- No statistical differences were noted in the mortality of the animals exposed to methyl methacrylate and those in the control group.

BODY WEIGHT AND WEIGHT GAIN
- Body weight depression observed at 2000 ppm did not persist beyond the first few weeks of the study.
- A statistically significant decrease in body weight was observed in the first week for the female rats and in weeks one through three in the male rats administered 2000 ppm methyl methacrylate.

FOOD CONSUMPTION
- Food consumption was not affected by the administration of methyl methacrylate in the drinking water. Individual observations of depressed food consumption tended to parallel periods of depressed growth. These effects were considered as temporary non-adverse effects.

WATER CONSUMPTION
- Significant depression of fluid consumption was observed at 2000 ppm, although this tended to regress at the end of the study.

HAEMATOLOGY
- Hematologic values varied within normal ranges in all groups of rats throughout the study.

URINALYSIS
- Urine concentrations of protein and reducing substances showed no trends that appeared relatable to treatment.

ORGAN WEIGHTS
- Organ to body weight ratios obtained at sacrifice of 2-year survivors differed from the controls only in significantly increased kidney ratios in female rats receiving 2000 ppm of methyl methacrylate (controls 0.0082 ± 0.0019; treated 0.0094 ± 0.0011). Since no substance-related effects were reported from histopathologic examinations in the kidneys, this effect is not considered as biologically relevant.

HISTOPATHOLOGY
- Histopathologic findings showed no abnormalities or lesions, in kind or incidence, not explicable on the basis of naturally occurring ones in this strain of rat at this age.

Key result

Dose descriptor:

NOAEL

Effect level:

> 2 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: see 'Remark'

- Diet equivalents of the test materials were calculated from the fluid and food consumption data.

- In these calculations, corrections were not made for evaporation losses of the test materials from the drinking water, the orders of magnitude of which are given under methods described above (maximum 15 %). Allowing for such losses, it would appear that the concentrations of test materials in the drinking water were equivalent to approximately 10, 100, and 3000 ppm in the diet.

Conclusions:

Under the study conditions, the No Observed Adverse Effect Level (NOAEL) of read across substance Methyl methacrylate was considered to be higher than 2000 ppm in rats. Similar results can be expected for zinc dimethacrylate.

Executive summary:

In a repeated dose oral toxicity study, read across substance Methyl methacrylate was administered by oral (drinking water) to groups of Wistar rats (25/sex/dose) at the dose-levels of 6, 60 and 2000 ppm at the start of the study; raised after 5 months to 7, 70 and 2000 ppm (limited by palatability) for 104 weeks (2 years). Examinations during the study included: mortality, body weight, food and water consumption, hematology, organ weights and histopathology. No statistical differences were noted in the mortality of the animals exposed to methyl methacrylate and those in the control group. Body weight depression observed at 2000 ppm did not persist beyond the first few weeks of the study. A statistically significant decrease in body weight was observed in the first week for the female rats and in weeks one through three in the male rats administered 2000 ppm methyl methacrylate. Food consumption was not affected by the administration of methyl methacrylate in the drinking water. Individual observations of depressed food consumption tended to parallel periods of depressed growth. These effects were considered as temporary non-adverse effects.Water consumption was reduced in the animals from the high-dose group; however, it was reported that this finding tended to regress towards the end of the study. Hematologic values varied within normal ranges in all groups of rats throughout the study. Urine concentrations of protein and reducing substances showed no trends that appeared relatable to treatment. There were significantly increased kidney weight ratios for female rats at 2000 ppm. Since no substance-related effects were reported from histopathological examinations in the kidneys, this effect is not considered as biologically relevant. Histopathological findings showed no abnormalities or lesions, in kind or incidence, not explicable on the basis of naturally occurring ones in this strain of rat at this age. Under these test conditions, the No Observed Adverse Effect Level (NOAEL) of read across substance Methyl methacrylate was considered to be higher than 2000 ppm in rats (Borzelleca, 1964). Similar results can be expected for zinc dimethacrylate.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the results of the carcinogenicity studies on zinc sulphate and methyl methacrylate, no classification is warranted for zinc methacrylate under the EU CLP Regulation (EC) 1272/2008. 

Additional information

Inhalation

In a carcinogenicity study performed similarly to OECD Guideline 451, read across substance Methyl methacrylate was administered via inhalation (whole body exposure) to groups of Fischer 344 rats (50/sex/dose) at the concentrations of 0, 500 and 1000 ppm (males) and 0, 250 and 500 ppm (females) for 102 weeks (6 h/day, 5 days/week). All animals were observed twice daily, and clinical signs were recorded once per week and bodyweights were recorded once per week for the first 13 weeks and once per month thereafter. Necropsy and histopathological examination performed on all animals at the end of study. No significant differences in survival were observed between any groups of either sex. Male and female rat body weights were lower at the 1000 ppm (5-10%) and 500 ppm (6-11%) exposure levels, respectively, presumably due to reduced food consumption due to nasal irritation and damage of olfactory epithelium. While food consumption was not recorded in this study this association is confirmed by two other studies, the developmental toxicity study with Methyl methacrylate with reduced food consumption and reduced body weight gain at concentrations higher than 99 ppm (Solomon, 1993) and a subchronic inhalation study with methacrylic acid where there was also an association of irritative effects in the nose and reduced food consumption and reduced body weight gain (BASF, 2008). Consequently, reduced body weight gain, while clearly treatment-related is considered to be secondary to the local effects in the nose and not the result of true systemic toxicity. The primary finding was inflammation of rat nasal cavity as well as olfactory epithelial degeneration at all exposure levels in male and female rats. In contrast to the 90 d range finding study with histopathological changes in females at exposures of 1000 ppm and above (Battelle, 1980), no other significant histopathological changes were reported in male and female rats after 104-week exposures to Methyl methacrylate vapour in this study. There was no treatment-related increase in tumour incidence. Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for rats; whereas the NOAEC for systemic effects and LOAEC for local effects (nasal irritation) were 500 ppm and 250 ppm, respectively (Chan, 1986). Similar results can be expected for zinc dimethacrylate.

 In a carcinogenicity study performed similarly to OECD Guideline 451, read across substance Methyl methacrylate was administered via inhalation (whole body exposure) to groups of mice (50/sex/dose) at the concentrations of 0, 500 and 1000 ppm for 102 weeks (6 h/day, 5 days/week). All animals were observed twice daily, and clinical signs were recorded once per week and bodyweights were recorded once per week for the first 13 weeks and once per month thereafter. Necropsy and histopathological examination performed on all animals at the end of study. Mean body weights of both male and female mice at both concentrations were lower than those of the controls throughout most of the study (males: up to 16% lower mean body weight; females: up to 17%). Acute and chronic inflammation, epithelial hyperplasia, cytoplasmic inclusions in the epithelial cells, and degeneration of the olfactory epithelium in the nasal cavity occurred at increased incidences in male and female mice exposed to the test substance. Accumulation of homogeneous, eosinophilic material in the cytoplasm of cells, primarily of the respiratory epithelium (cytoplasmic inclusions) was significantly increased in treated animals when compared to that of the controls. Uterine adenocarcinomas were reduced in animals from both of the treatment groups, but statistical significance was not observed. In the lungs, interstitial inflammation was increased in the male mice from the high-group, while alveolar/bronchiolar adenomas and alveolar/bronchiolar adenomas and carcinomas (combined) were significantly reduced in the male mice exposed to 500 and 1000 ppm. Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for mice; whereas the NOAEC for systemic and LOAEC for local effects (nasal irritation) were 500 ppm and 250 ppm, respectively (Chan, 1986). Similar results can be expected for zinc dimethacrylate.

   

In a combined chronic toxicity/carcinogenicity study in F344 rats, 70 male and 70 female F344 rats were exposed to vapor concentrations of 0, 25, 100 or 400 ppm read across substance methyl methacrylate for two years. Ten male and ten female rats from all groups were sacrificed after 13 and 52 weeks of exposure and all surviving rats were killed during week 104-106. Histological examination was conducted on more than 35 tissues including 3-4 cross-sections of the nasal cavity. Tissues from the trachea and the pharynx/larynx were not preserved for histopathologic examination. Mortality rates of treatment and control groups did not show significant differences. No compound-induced clinical signs were observed. After week 52, mean body weight of high dose females was generally lower than controls gaining intermittently significance. Reduced growth represented the only adverse effect outside the respiratory tract. Evaluation of hematology, clinical chemistry and urinalysis data did not reveal any methyl methacrylate associated effect. At the end of the study, there were weight changes of some organs in males or females without any consistent relationship to the treatment. Similarly, no treatment-related macroscopic findings were observed in any of the dose groups. No histomorphological lesions other than nasal lesions were attributable to methyl methacrylate exposure of any exposed group. The examination of nasal cavities from male and female rats exposed to 400 ppm for 13 weeks or 52 weeks revealed a degeneration of the neuroepithelial olfactory cells lining the dorsal meatus of the anterior portions of the nasal cavities in conjunction with atrophy of Bowman’s glands and focal basal cell hyperplasia. Chronic active inflammation, respiratory epithelial hyperplasia and squamous metaplasia characterized the lesions on the tips of the maxilloturbinate and nasoturbinats and focally along the nasal septum in more anterior regions of the nose. At the final sacrifice, nasal lesions were evident in males and females of the 100 ppm and 400 ppm exposure groups characterised by inflammatory degeneration of nasal epithelium (Lomax, 1997). Under the study conditions, there was no evidence of carcinogenic activity of read across substance Methyl methacrylate for rats; whereas the NOAEC for systemic and LOAEC for local effects (nasal irritation) were considered as 400 ppm and 100 ppm, respectively. Similar results can be expected for zinc dimethacrylate.

 

Oral

 

In a repeated dose oral toxicity study, read across substance Methyl methacrylate was administered by oral (drinking water) to groups of Wistar rats (25/sex/dose) at the dose-levels of 6, 60 and 2000 ppm at the start of the study; raised after 5 months to 7, 70 and 2000 ppm (limited by palatability) for 104 weeks (2 years). Examinations during the study included: mortality, body weight, food and water consumption, hematology, organ weights and histopathology. No statistical differences were noted in the mortality of the animals exposed to methyl methacrylate and those in the control group. Body weight depression observed at 2000 ppm did not persist beyond the first few weeks of the study. A statistically significant decrease in body weight was observed in the first week for the female rats and in weeks one through three in the male rats administered 2000 ppm methyl methacrylate. Food consumption was not affected by the administration of methyl methacrylate in the drinking water. Individual observations of depressed food consumption tended to parallel periods of depressed growth. These effects were considered as temporary non-adverse effects.Water consumption was reduced in the animals from the high-dose group; however, it was reported that this finding tended to regress towards the end of the study. Hematologic values varied within normal ranges in all groups of rats throughout the study. Urine concentrations of protein and reducing substances showed no trends that appeared relatable to treatment. There were significantly increased kidney weight ratios for female rats at 2000 ppm. Since no substance-related effects were reported from histopathological examinations in the kidneys, this effect is not considered as biologically relevant. Histopathological findings showed no abnormalities or lesions, in kind or incidence, not explicable on the basis of naturally occurring ones in this strain of rat at this age. Under these test conditions, the No Observed Adverse Effect Level (NOAEL) of read across substance Methyl methacrylate was considered to be higher than 2000 ppm in rats (Borzelleca, 1964). Similar results can be expected for zinc dimethacrylate.

A chronic study was conducted to evaluate the carcinogenic potential of the read across substance zinc sulphate in mice. Chester Beatty stock mice (newly-born litters) were used. They were housed in the metal cages (4-6 per cage). The doses of zinc sulphate were 22 g/L (5,000 ppm zinc) and 4.4 g/L (1,000 ppm zinc) in drinking water along with a control group fed a basal diet and normal drinking water. The animals were examined thoroughly once a wk throughout the experiment and daily when fed. Weighing was done once every 2 wk. Deaths of animals occurred during the first 8 wk of experiment due to an epizootic of ectromelia. The survivors were vaccinated with sheep lymph and animals showing a negative or accelerated response were sacrificed. New group of weanling mice (4 -5 wk old) were added to supplement the control group. All the surviving animals were sacrificed after 1 year of treatment and examined for gross pathology. Histopathological examination was done for suspected neoplastic lesions. Stomachs were examined for tumours and other changes in the forestomach and glandular epithelium. No differences in carcinogenic effects were observed between treatment and control groups under the test conditions. Under the test conditions, zinc sulphate was found to be non-carcinogenic in mice (Walters, 1965).