Styrene

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well-documented publication/report meeting basic scientific principles. Oral study in rats and mice.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1979

Reference 2

Reference Type:

secondary source

Title:

European risk assessment report, Styrene CAS No. 100-42-5, EINECS No. 202-851-5, Draft for submission to SCHER, November 2007.

Author:

European Union

Year:

2007

Bibliographic source:

European risk assessment report, Styrene CAS No. 100-42-5, EINECS No. 202-851-5, Draft for submission to SCHER, November 2007.

Materials and methods

Principles of method if other than guideline:

A bioassay for the possible carcinogeniclty of styrene was conducted using Fischer 344 rats. Styrene was administered by gavage for 78 to 103 weeks to groups of 50 male and 50 female animals. The high, medium, and low dosages administered were, respectively, 2000, 1000 and 500 mg/kg. The period of compound administration was followed by an observation poriod of 27 weeks for high and medium dose rate and 1 week for low dose rate.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Styrene

EC Number:

202-851-5

EC Name:

Styrene

Cas Number:

100-42-5

Molecular formula:

C8H8

IUPAC Name:

ethenylbenzene

Details on test material:

- Name of test material (as cited in study report): styrene (6 batches, batch 1 from Dow Chemical Company, Midland, Michigan; batch 6 from Amoco Chemicals Corporation, Chicago, Illinois, origin of 4 batches unknown)
- Impurities (identity and concentrations): t-butylcatochol as an inhibitor.

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: A. R. Schmidt, Madison, Wisconsin, and Breeding Laboratories, Inc., Wilmington, Massachusetts
- Age at study initiation: approximately 6 weeks
- Weight at study initiation: no data
- Fasting period before study: no
- Housing: 4/sex/polycarbonate cages (Lab products, Inc., Garfield, New Jersey) suspended from aluminium racks
- Diet: Lab Blox meal ad libitum
- Water: acidulated (pH 2.5) water ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22-26
- Humidity (%): 45-55
- Air changes (per hr): 12-15
- Photoperiod (hrs dark / hrs light): 16 / 8

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
The concentrations of styrene in corn oil ranged from 21.5 to 43 percent.
The inhibitor, t-butylcatechol was removed from the test material with anhydrous calcium sulphate (white Drierite) 2 to 4 weeks prior to dosage preparation. Drierite crystals were placed in the styrene and refrigerated at 4°C for a 2-to 4-week period. The treated styrene was mixed with corn oil (Great Atlantic & Pacific Tea Company, New Baltimore, Maryland) and used within 2 hours. Excess portions of the corn oil and styrene mixtures were disposed rather than stored.


VEHICLE
- Concentration in vehicle: 455 mg styrene/mL

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

78 weeks to high and medium dose rats and for 103 weeks to low dose rats. Due to excessive mortality in the high and medium dose groups, an additional group of male and female rats were placed in test in week 23. These rats were treated for 103 weeks, followed by a 1-week observation period.

Frequency of treatment:

daily (5 days/week)

Doses / concentrations

Remarks:

Doses / Concentrations:
500, 1000 and 2000 mg/kg
Basis:
actual ingested

No. of animals per sex per dose:

50

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: subchronic toxicity testing with 681, 1000, 1470, 2150 and 3160 mg styrene/kg body weight for 7 weeks followed by a 1-week observation period.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily


BODY WEIGHT: Yes
- Time schedule for examinations: high dose, medium dose, and high and medium dose vehicle control rats prior to study initiation, once a week for the first 6 weeks, every 2 weeks for the next 12 weeks, and at monthly intervals thereafter.


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Monthly intervals from 20 percent of the animals in each group.


No further observations or examinations.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes; all major tissues, organs, and gross lesions.
HISTOPATHOLOGY: Yes
skin, subcutaneous tissue, lungs and bronchi, trachea, bone marrow, spleen, lymph nodes, thymus, heart, salivary gland, liver, pancreas, esophagus, stomach, small intestine, large intestine, kidney, urinary bladder, pituitary, adrenal, thyroid, parathyroid, testis, prostate, brain, uterus, mammary gland, and ovary.

Statistics:

Kaplan-Meier procedure, Cox test (survival), Tarone's extension of Cox's method (dose-response-relationship), Fisher exact test, Cochran-Armitage test, life-table methods (tumour incidence)

Results and discussion

Results of examinations

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY: Mortality: male rats: high dose: 12 percent (6/50) survived on test past week 53; 94 percent (47/50) of the medium dose, 88 percent (44/50) of the low dose, 90 percent (18/20) of the high and medium dose vehicle controls and 85 percent (17/20) of the low dose vehicle controls survived on test for at least 90 weeks; females: high dose: 14 percent (7/50) were dead by week 70; 92 percent (46/50) of the medium dose, 92 percent (46/50) of the low dose, 90 percent (18/20) of the high and medium dose vehicle controls and 75 percent (15/20) of the low dose vehicle controls survived on test for at least 90 weeks. No clinical signs were recorded.

BODY WEIGHT AND WEIGHT GAIN: Distinct dose-related mean body weight depression was apparent in male rats. In female rats the mean body weight among the medium dose group was slightly less than that of their vehicle control

HISTOPATHOLOGY: NON-NEOPLASTIC: A variety of sporadic (no dose-response) inflammatory, degenerative and proliferative lesions commonly seen in aged Fischer 344 rats was observed in dosed and vehicle control animals. Hepatic necrosis, observed in several of the high dose rats, may be related to the high mortality observed in these groups.

HISTOPATHOLOGY: NEOPLASTIC: A variety of neoplastic lesions was seen with approximately equal frequency in the vehicle control and dosed rats. In the high dose rats of both sexes, there was a distinct lack of neoplasia. This was most likely due to a large number of early deaths which occurred in high dose rats.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: mortality; histopathology (hepatic necrosis)

2

Dose descriptor:

LOAEL

Effect level:

2 000 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: mortality; histopathology (hepatic necrosis)

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

The Cox test for comparison of survival of a dosed group relative to its vehicle control was significiat for high dose males (P < 0.001) and high dose females (P < 0.001). There were inadequate numbers of high dose male rats at risk from late-developing tumors as only 12 percent (6/50) survived on test past veek 53. Survival was adequate in the other rat group, as 94 percent (47/50) of the medium dose, 88 percent (44/50) of the low dose, 90 percent (18/20) of the high and medium dose vehicle control and 85 percent (17/20) of the low dose vehicle controls survived on test for at least 90 weeks. An increased incidence of alveolar/bronchiolar neoplasms was observed in dosed male. Mortality among male and female high dose rats was significantly higher than that among their respective vehicle controls. In response to this elevated and early mortality, an additional dosed group of each sex was included in the chronic bioassay. No significant positive association was apparent between dosage and mortality among any other dosed rat groups.