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control; females: 6/10 exposed, 0/14 control; p < 0.01). Other tumors noted in exposed animals but
not control animals include single cases of thyroid adenoma and liver hemangiosarcoma in males,
malignant lymphoma and bronchial adenoma in females.
Toth et al. (1961a) exposed Syrian golden hamsters (31 male; 30 female) to drinking water containing
0.2% urethane. Control groups of 54 male and 47 female received plain drinking water. Dosing began
at 5 weeks and continued to 25 weeks at which point the drinking water urethane concentration was
increased to 0.4%. At 40 weeks treatment was discontinued due to diarrhea among the animals. At 48
weeks, treatment with 0.4% urethane resumed, but was discontinued permanently at 50 weeks due to
diarrhea. Survival was significantly decreased in exposed male and female hamsters. Among exposed
animals, significant increases in incidence of dermal melanotic tumors (12/27 exposed males vs. 0/54
control males; 11/25 exposed females vs. 0/47 control females; p ≤ 10 -6 ; Fisher’s exact test),
forestomach papillomas (22/27 exposed vs. 0/54 control, p < 10 -15 , males; 18/25 exposed vs. 1/47
control; p < 10 -9 , females) and carcinomas (3/27 exposed vs. 0/54 control; p = 0.04, males; 2/25
exposed vs. 0/47 control; p = 0.1, females), pulmonary adenomatosis (3/27 exposed vs. 0/54 control;
p = 0.04, males), mammary tumors (3/25 exposed vs. 0/47 control; p = 0.04, females), hepatomas
(3/27 exposed vs. 0/54 control; p = 0.04, males), and hepatic or splenic hemangiomas (5/27 exposed
vs. 0/54 control; p = 0.04, males) were found.
Toth and Boreisha (1969) exposed Syrian golden hamsters (48 male and 52 female) to drinking water
containing 0.1% urethane for life, beginning at 5 weeks of age. Control groups (100/sex) received plain
drinking water. Survival was significantly decreased in exposed male and female animals. An increased
incidence of dermal melanocytosis (26/49 exposed males vs. 1/88 control males; 25/41 exposed
females vs. 0/79 control females; p = 10 -14 ; Fisher’s exact test), forestomach papillomas (36/49
exposed vs. 6/88 control, p = 10 -15 , males; 35/44 exposed vs. 2/84 control, p = 10 -20 , females) and
adenomatous polyps of the cecum (4/40 exposed vs. 0/79 control, p = 0.01, males; 7/33 exposed vs.
0/72 control, p = 0.001, females) was noted in both males and female animals. Among females an
increased incidence of gall bladder papillomas, adrenal cortex carcinomas, thyroid carcinomas, ovarian
carcinomas, vaginal carcinomas, and lung adenomatosis was observed (p < 0.05). Hemangiosarcoma
incidence was increased in exposed males.
Tannenbaum et al. (1962) exposed Sprague-Dawley rats (15/group) to drinking water containing 0.1%
urethane. Two “young” groups, one virgin females and the other males, were treated from age 7 weeks
to 32 weeks. A third group of virgin females was treated for 14 weeks from age 32 weeks. Age and
sex matched control groups of 15 each receiving plain drinking water were included in the study.
Animals were autopsied at the time of natural death unless sacrificed when moribund. Survival was
reduced in the treated groups. Incidence of Zymbal gland carcinoma was increased in treated “young”
male rats (4/15 treated vs. 0/15 control, p = 0.05, Fisher’s exact test) and female rats (3/15 treated vs.
0/15 control, p = 0.11). Control animals showed higher incidence of mammary tumors than treated
animals, most likely because of the reduced survival of treated animals. Tumors noted among treated
animals, but not control animals, include malignant lymphoma, sarcoma, and kidney tumors.
Schmähl et al. (1977) and Port (1976) report on exposure of rats and mice to urethane in drinking
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