home edit2 whole TSD November 2002 PDF format - OEHHA

male and female rats. Tumor incidences were 0/10, 2/26 and 15/26 in pooled control, low-dose and
high-dose male rats, respectively, and 0/10, 2/26 and 6/26 in pooled control, low-dose and high-dose
female rats, respectively.
IV.
DERIVATION OF CANCER POTENCY
Basis for Cancer Potency
The results of several studies are listed in Gold et al. (1984). Innes et al. (1969) administered ethylene
thiourea (ETU) to small groups of both sexes of B6C3F 1 and B6AKF 1 mice; Graham et al. (1973,
1975) performed relatively large multiple dose studies in Charles River CD rats of both sexes;
Weisburger et al. (1981) and Ulland et al. (1972) conducted moderately sized studies in male and
female Charles River CD rats. Because all male B6C3F 1 and female B6AKF 1 mice treated with ETU
developed liver tumors, an upper bound estimate on potency could not be determined for these studies.
The lower bound estimates of cancer potency derived from the mouse data are consistent with
potencies derived from the studies in rats. Further, cancer potencies derived from the rat studies are
consistent with one another. The value selected is derived from the highest quality study, Graham
(1973, 1975), which had a large sample size and used multiple dose groups. The target site chosen for
the analysis was the thyroid in the Charles River CD rats, the most sensitive site (see Table 2)
(Cal/EPA, 1992).
Methodology
Expedited Proposition 65 methodology (with cross-route extrapolation) was used to derive a cancer
potency factor. A unit risk factor was then calculated by OEHHA/ATES from the cancer potency
factor using a reference human body weight of 70 kg and an inspiration rate of 20 m 3 /day.
V. REFERENCES
Bionetics Research Labs, I. 1968. Evaluation of Carcinogenic, Teratogenic and Mutagenic Activities of
Selected Pesticides and Industrial Chemicals. Volume I. Carcinogenic study. Prepared for National
Cancer Institute. NTIS Publication No. PB-223 159.
California Environmental Protection Agency (Cal/EPA) 1992. Expedited Cancer Potency Values and
Proposed Regulatory Levels for Certain Proposition 65 Carcinogens. Office of Environmental Health
Hazard Assessment, Reproductive and Cancer Hazard Assessment Section, Berkeley, CA.
Gold L, Sawyer C, Magaw R, Backman G, de Veciana M, Levinson R, Hooper N, Havender W,
Bernstein L, Peto R, Pike M and Ames B. 1984. A Carcinogenic Potency Database of the
standardized results of animal bioassays. Environ Health Perspect 58:9-319.
Graham SL, Davis KJ, Hansen WH and Graham CH. 1975. Effects of prolonged ethylene thiourea
ingestion on the thyroid of the rat. Food Cosmet Toxicol 13:493-499.
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