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species, sex and study, in the absence of evidence that the data are not representative. The Innes et
al.(1969) study presents the highest, and thus most sensitive, cancer potency value of 0.061 (mg/kgday)
-1 . The lower 95% confidence bound on the Innes et al. (1969) potency value
also exceeds the potency values derived from Cardy et al. (1979) indicating the mouse strain used by
Innes et al. (1969) may be more sensitive. The small number of animals used in this preliminary study,
however, suggests the possibility this value may be overly conservative. The two q human values for
NDPA in male and female rats derived from Cardy et al. (1979) are close, 0.0032 and 0.0034
(mg/kg-day) -1 , respectively. Since these data were derived from a large, thorough study, the
development of a reference cancer potency value should include these values. The potency estimate
was therefore derived from the geometric mean of the three q human values described above according to
the approach of Anderson et al. (1983). The resulting reference q human is 0.009 (mg/kg-day) -1 .
A unit risk value based upon air concentrations was derived by OEHHA/ATES using an assumed
human breathing rate of 20 m 3 /day, 70 kg human body weight, and 100% fractional absorption after
inhalation exposure. The calculated unit risk value is 2.6 E-6 (µg/m 3 ) -1 .
V. REFERENCES
Anderson EL and the US Environmental Protection Agency (US EPA). 1983. Quantitative
approaches in use to assess cancer risk. Risk Anal 3:277-295.
Argus MF, and Hoch-Ligeti, AM. 1961. Comparative study of the carcinogenic activity of
nitrosamines. J Natl Cancer Inst 27:695-709.
Boyland E, Carted RL, Gorrod JW, Roe FJC. 1968. Carcinogenic properties of certain rubber
additives. Eur J Cancer 4:233-239.
California Department of Health Services (CDHS). 1985. Guidelines for Chemical Carcinogen Risk
Assessment and Their Scientific Rationale. CDHS, Health and Welfare Agency, Sacramento, CA.
California Department of Health Services (CDHS). 1988. Proposition 65 Risk-Specific Levels: N-
Nitrosodiphenylamine. Reproductive and Cancer Hazard Assessment Section, Office of Environmental
Health Hazard Assessment, Berkeley, CA.
Cardy RH, Lijinsky W, Hildebrandt PK. 1979. Neoplastic and nonneoplastic urinary bladder lesions
induced in Fischer 344 rats and B6C3F 1 hybrid mice by N-nitrosodiphenylamine. Ecotoxicol Environ
3:29-35.
Crouch EAC. 1983. Uncertainties in interspecies extrapolation of carcinogenicity. Environ Health
Perspect 5:321-327.
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