(chloromethyl)vinylbenzene

Carcinogenicity

Administrative data

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1976

Report date:

1976

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study was conducted before the time of adoption of OECD Test Guidelines on carcinogenicity and combined chronic toxicity/carcinogenicity.
6-month exposure period of 144-159 mice per dose level, with consecutive observation of most of the animals for their whole lifespan (maximum 25 months), and pathological as well as histopathological examination of lungs and liver after necropsy

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

(chloromethyl)vinylbenzene

EC Number:

250-005-9

EC Name:

(chloromethyl)vinylbenzene

Cas Number:

30030-25-2

Molecular formula:

C9H9Cl

IUPAC Name:

1-(chloromethyl)-3-ethenylbenzene; 1-(chloromethyl)-4-ethenylbenzene

Test material form:

liquid

Details on test material:

The test sample of vinylbenzyl chloride was 98.49% pure with 0.14% of vinyl toluene, 0.20% of alpha chlorinated vinyl toluene, 0.47% of beta chlorinated vinyl toluene, 0.23% of dichloroethyl toluene and 0.24% of unknown a impurities.
The sample contained 67.91% meta- and 30.58% para-isomers of vinylbenzyl chloride.

Test animals

Species:

mouse

Strain:

Swiss Webster

Sex:

not specified

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

Exposures were conducted in 3.7 m3 stainless steel chambers under dynamic airflow conditions. The exposure atmosphere in each chamber was generated by metering liquid vinylbenzyl chloride into a heated glass vaporizer at a calculated rate. The vapors emerging from the vaporizer were diluted with room air at a rate to provide the desired test material concentration. The nominal concentration in the chamber atmosphere was the ratio of the rate of vinylbenzyl chloride delivery to the rate of total chamber airflow (the volume of air ejected from the vaporizer plus the volume of make-up air).

Analytical verification of doses or concentrations:

yes

Remarks:

by gas chromatography, two times on 124 or 125 days

Details on analytical verification of doses or concentrations:

20 L of air from the exposure chamber were drawn at the rate of 1 L/min through 25 mL of cold methanol in a fritted bottom bubbler. The vinylbenzyl chloride (VBC) dissolved in methanol was extracted with 10 mL of carbon disulfide. The quantity of VBC in a 2 µL sample of VBC-CS2 solution was analyzed by means of a gas chromatographic technique. The concentration of VBC in each sample was found by interpolation from a curve prepared with standard VBC solutions in CS2.

There were some day-to-day variations in chamber VBC concentration. However, 80-90% of the total exposure days were within +50% of the designated levels. There was no overlapping of concentration between the high and low range throughout the exposure period.

Duration of treatment / exposure:

6 hours per day

Frequency of treatment:

5 days per week (months 1-6 of study)

Post exposure period:

months 7-25 of study

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0.1 ppm (nominal)

Doses / concentrations 2

Dose / conc.:

1 ppm (nominal)

No. of animals per sex per dose:

144-159

Control animals:

yes, concurrent vehicle

yes, historical

Details on study design:

In total, animals were exposed on 131 days in 6 months. Food and water were removed from all animals during the exposure period. Even though controls were not placed in chambers, food and water were removed from them during the exposure period. After the 6 month exposure period, the mice were kept under ambient conditions and observed for the duration of their lifespan (maximum of 25 months).

Examinations

Observations and examinations performed and frequency:

Animals were observed throughout the study for changes and demeanor. Body weights were recorded once a week for 3 months of the study and monthly thereafter.

Sacrifice and pathology:

All mice were held for observation until they died or were killed in a moribund condition. Each mouse was subjected to a thorough necropsy examination, with specific emphasis on the presence or absence of tumorous lesions. All major organs and tissues were preserved in 10% formalin. Microscopic examination was conducted on all lungs and livers in which gross necropsy examination had revealed the presence of nodular lesions suggestive of a proliferative pathologic process, such as tumor formation.

Statistics:

Statistical analysis of body weights were carried out using an analysis of variance and Dunnett's Test. The mortality data and tumor incidence were analyzed with Fisher's Exact Probability Test. The level of significance in all statistical analysis was p <0.05.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

During the exposures, the mice exposed to 1 ppm vinylbenzyl chloride (VBC) exhibited slight transient eye and nasal irritation. The signs of irritation disappeared soon after termination of exposure to VBC each day.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Examination of the mortality data for mice reveals that deaths began to occur soon after initiation of exposure. Deaths of exposed mice began to accelerate by the fifth exposure week and continued until the second or third month of the post-exposure period. For the control mice, there were no deaths until the third month of the exposure period, at which time a similar mortality pattern began to occur. Necropsy examination revealed an ascending urinary tract infection in a majority of these mice. This presented as a necrotic purulent balanoposthitis, purulent urethritis, urinary retention in the urinary bladder and urocystitis. Microbiological cultures from these cases revealed the presence of various bacterial organisms, including species of Salmonella, Proteus, Pseudomonas, E. coli and Staphylococcus. Some of the mice had traumatic lesions indicative of cannibalism.

Body weight and weight changes:

no effects observed

Food efficiency:

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Lungs and livers of the mice were examined for tumors. Pulmonary adenomas and carcinomas as well as benign hepatic tumors, hepatocellular carcinomas and angiosarcomas in liver were distinguished by gross pathological and histopathological inspection (see histopathological findings, non-neoplastic).

Neuropathological findings:

not specified

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

Lungs and livers of the mice were examined for tumors. Pulmonary adenomas and carcinomas as well as benign hepatic tumors, hepatocellular carcinomas and angiosarcomas in liver were distinguished by gross pathological and histopathological inspection.

Pulmonary adenomas and adenocarcinomas, both of probable alveolar origin, were noted in both control and two exposed groups of mice, with a lower incidence in the exposed groups of mice. The pulmonary tumors observed in the mice of this study were of the type commonly observed as spontaneous occurrences in mice of this strain. The temporal occurrence of the pulmonary tumors within intervals of six months did not appear to be influenced by exposure to vapors of vinylbenzyl chloride (VBC).

Some mice from control and exposed groups showed gross and microscopic evidence of liver tumors. The incidence was highest in the control group. Tumors of hepatocellular origin included one morphologically benign hepatic tumor in a mouse of the 1.0 ppm VBC group and 4 morphologically malignant hepatocellular carcinomas, of which 3 out of 4 occurred i n the control group and one out of 4 occurred in the low exposure (0.1 ppm) group. In the liver of one control mouse a tumorous mass was found which was considered to be a hemangioma. No tumors of this latter type were noted in the groups of mice exposed to vapors of VBC.

Other effects:

not specified

Relevance of carcinogenic effects / potential:

The occurance of benign and malign lung and liver tumors, which in total were more frequently found in the control group, was distinguished by gross pathological and histopathological examination. The incidence of these tumors did not appear to be influenced by exposure to vapors of vinylbenzyl chloride (VBC).

Effect levels

Key result

Dose descriptor:

NOAEC

Effect level:

ca. 1 ppm (nominal)

Basis for effect level:

gross pathology

histopathology: neoplastic

Applicant's summary and conclusion

Conclusions:

The results of this study are interpreted to indicate that lifetime observation of mice inhaling 0.1 or 1.0 ppm VBC for 6 hours/day, 5 days per week for 6 months had no discernible ill effects, including carcinogenesis in lungs and liver, except for clinically observed reversible eye and nasal irritation in animals exposed to the 1.0 ppm level of VBC.

Executive summary:

Groups of 144 -159 Swiss Webster mice were exposed to atmospheres containing 0, 0.1 and 1.0 ppm of vinylbenzyl chloride (VBC) 6 hours/day, 5 days/week for 6 months and subsequently observed for their natural lifespan (at maximum for 25 months). There was clinical evidence of slight reversible eye and nasal irritation during exposure to 1 ppm VBC but not during inhalation of 0.1 ppm VBC. Body weight of control and treatment groups showed no significant differences. An increased mortality observed from the fifth week in exposure groups and from the ninth week in control animals was considered to be not treatment-related as necropsy examination revealed an ascending urinary tract infection in a majority of these mice. The occurance of benign and malign lung and liver tumors, which in total were more frequently found in the control group, was distinguished by gross pathological and histopathological examination. The incidence of these tumors did not appear to be influenced by exposure to vapors of vinylbenzyl chloride (VBC).

The results of this study are interpreted to indicate that lifetime observation of mice inhaling 0.1 or 1.0 ppm VBC for 6 hours/day, 5 days per week for 6 months had no discernible ill effects, including carcinogenesis in lungs and liver, except for clinically observed reversible eye and nasal irritation in animals exposed to the 1.0 ppm level of VBC.