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female dogs received toothpaste base with 0, 15 or 30 mg chloroform/kg-day, 6 days/week for 7.5<br />

years (8-16 dogs/sex), followed by a 20-24 week recovery period. Treatment with chloroform at the<br />

high dose was associated with significant elevations in SGPT levels but no treatment-related tumors<br />

were observed.<br />

Chloroform treatment of rats via drinking water was associated with hepatic neoplastic nodules and<br />

hepatic adenofibrosis (Tumasonis et al., 1985). Chloroform was administered to male and female<br />

Wistar rats in the drinking water at about 220 mg/kg/day and 160 mg/kg/day for the female and male<br />

rats, respectively. The incidence of hepatic neoplastic nodules was significantly elevated in treated<br />

females compared to controls (p < 0.03, Fisher exact test). In males, the incidence of hepatic<br />

neoplastic nodules did not differ in control and chloroform-treated groups. Increased incidences of<br />

hepatic adenofibrosis were observed in chloroform-treated males and females relative to controls. In<br />

contrast to the NCI and the Jorgenson et al. studies, renal tumors were not associated with chloroform<br />

treatment. However, Tumasonis et al. indicated that kidneys were only examined when grossly<br />

observable lesions were evident. Hence, kidney tumors may have been missed by this protocol.<br />

Tumasonis et al. concluded that chloroform is a hepatocarcinogen in Wistar rats.<br />

Table 1:<br />

Chloroform carcinogenicity bioassay tumor incidence data used to estimate<br />

cancer potency (CDHS, 1990)<br />

Study Strain/Species Sex Tumor Site Lifetime Daily Dose<br />

(mg/kg-day)<br />

NCI (1976) B6C3F 1 mouse M hepatocellular carcinoma control<br />

83<br />

167<br />

Jorgenson<br />

et al. (1985)<br />

Roe et al.<br />

(1979)<br />

B6C3F 1 mouse F hepatocellular carcinoma control<br />

143<br />

287<br />

Osborne-Mendel rat M renal tubular adenoma or<br />

adenocarcinoma<br />

Osborne-Mendel rat M renal tubular adenoma or<br />

adenocarcinoma<br />

ICI mouse<br />

(Experiment I)<br />

ICI mouse<br />

(Experiment II)<br />

M<br />

M<br />

renal tubular adenoma or<br />

adenocarcinoma<br />

renal tubular adenoma or<br />

adenocarcinoma<br />

ICI mouse<br />

M renal tubular adenoma or<br />

(Experiment III) a adenocarcinoma<br />

ICI mouse<br />

M renal tubular adenoma or<br />

(Experiment III) b adenocarcinoma<br />

control<br />

45<br />

90<br />

control<br />

18<br />

38<br />

79<br />

155<br />

control<br />

12<br />

43<br />

control<br />

40<br />

control<br />

42<br />

control<br />

42<br />

Tumor<br />

Incidence<br />

1/18<br />

18/50<br />

44/45<br />

0/20<br />

36/45<br />

39/41<br />

0/19<br />

4/38<br />

12/27<br />

4/301<br />

4/313<br />

4/148<br />

3/48<br />

7/50<br />

0/72<br />

0/37<br />

8/37<br />

6/237<br />

9/49<br />

1/49<br />

5/47<br />

1/50<br />

12/48<br />

196

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