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dose group; in addition, 3/12 animals exposed to the 5000 mg/kg diet for 10 weeks had thyroid tumors.
Clitoral gland tumors (squamous-cell, sebaceous-cell or squamous-sebaceous-cell carcinomas) were
noted in 0/37 controls, 8/47 of the low-dose group, 15/33 of the mid-dose group and 9/40 of the high
dose-group, as well as in 1/12 of the animals in the 10 week high-dose group.
IV.
DERIVATION OF CANCER POTENCY
Basis for Cancer Potency
Cancer potency for 2, 4-diaminoanisole was derived from that for the sulfate using a molecular weight
conversion (Cal/EPA, 1992):
q h (base) = q h (sulfate) ×
MW(sulfate)
MW(base)
where q h is the human potency and MW is the molecular weight. This conversion assumes that the
intake of equivalent moles of the two forms of the chemical results in equivalent concentrations of the
active species in vivo. Gold et al. (1984) list the results of the NCI (1978) feeding studies in male and
female F344 rats and B6C3F 1 mice, and the feeding study by Evarts and Brown (1980) in female F344
rats. Cancer potency is based on dose-response data for benign and malignant thyroid tumors in male
rats, the most sensitive sex and species (see Table 1) (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
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.
Evarts RP and Brown CA. 1980. 2,4-diaminoanisole sulfate: early effect on thyroid gland morphology
and late effect on glandular tissue of Fischer 344 rats. J Natl Cancer Inst 65:197-204.
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.
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