home edit2 whole TSD November 2002 PDF format - OEHHA

male or female rats. Increases in hepatocellular carcinoma incidence were noted in all male and female
mouse 1,1,2-trichloroethane-exposed treatment groups. The Fisher exact test comparing tumor
incidences of dosed to control groups and the Cochran-Armitage test for positive dose-related trend
indicated a highly significant association (p < 0.001) between hepatocellular carcinomas and 1,1,2-
trichloroethane exposure. A positive dose-related association between 1,1,2-trichloroethane exposure
and adrenal gland pheochromocytoma incidence in male and female mice was also indicated by the
Cochran-Armitage test (p = 0.003 for males, p < 0.001 for females). Fisher exact tests confirmed
these results for high dose female mice (p = 0.006) but not for other mouse treatment groups. Mouse
tumor incidence data is listed in Table 1.
Table 1.
1,1,2-Trichloroethane-induced B6C3F 1 mouse tumor incidence data
(NCI, 1978)
Treatment group 1
(mg/kg/day)
Time-weighted 2
average dose
(mg/kg/day)
Human equivalent
dose 2
(mg/kg/day)
Tumor incidence 3
hepatocellular carcinomas
males
vehicle control 0 0 2/20
low dose 139 9.3 18/49
high dose 279 18.6 37/49
females
vehicle control 0 0 0/20
low dose 139 9.3 16/48
high dose 279 18.6 40/45
1. Low and high doses: 150 and 300 mg/kg body weight, respectively, for 8 weeks, followed by
200 and 400 mg/kg, respectively, for 70 weeks, followed by 12-13 weeks without treatment.
2. Doses as reported by US EPA (1994).
3. Tumor incidences as reported by US EPA (1994).
IV.
DERIVATION OF CANCER POTENCY
Basis for Cancer Potency
The NCI (1978) carcinogenicity bioassay of 1,1,2-trichloroethane indicated that 1,1,2-trichloroethane
induced tumor formation in male and female B6C3F 1 mice. The cancer potency value is based on the
dose-response data for hepatocellular carcinomas in male mice.
520