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interpretation of dose extrapolation, preclude the development of cancer potency values from these<br />

studies.<br />

Methodology<br />

The most sensitive experimentally determined endpoint for tumor development is mammary<br />

adenocarcinoma induction in female rats exposed to 3,3’-dichlorobenzidine (26/44 treated, 3/44<br />

control) (Stula et al., 1975). A linearized multistage procedure (CDHS, 1985) applied to these data<br />

resulted in an estimation of the upper 95% confidence bound of cancer potency (q 1 * ) of 0.023 (mg/kgday)<br />

-1 . With a study duration of 49.9 weeks for females (T e ) and a natural lifespan assumption of 104<br />

weeks (T), the cancer potency for animals (q animal ) was derived to be 0.21 (mg/kg-day) -1 from the<br />

following relationship:<br />

q animal = q 1 * × (T/T e ) 3<br />

Human cancer potency (q human ) of 1.2 (mg/kg-day) -1 based upon body weight assumptions of 0.35 kg<br />

for female rats (bw a ) and 70 kg for humans (bw h ) and the following relationship:<br />

q human = q animal × (bw h /bw a ) 1/3<br />

A unit risk value of 3.4 E-4 (µg/m 3 ) -1 based upon air concentrations was derived by <strong>OEHHA</strong>/ATES<br />

assuming a human breathing rate of 20 m 3 /day, a human body weight of 70 kg, and 100% fractional<br />

absorption after inhalation exposure.<br />

V. REFERENCES<br />

California Department of Health Services (CDHS). 1985. Guidelines for Chemical Carcinogen Risk<br />

Assessment and Their Scientific Rationale. CDHS, Health and Welfare Agency, Sacramento, CA.<br />

California Department of Health Services (CDHS). 1988. Proposition 65 Risk-Specific Levels: 3,3’-<br />

Dichlorobenzidine. Reproductive and Cancer Hazard Assessment Section (RCHAS), Office of<br />

Environmental Health Hazard Assessment (<strong>OEHHA</strong>), Berkeley, CA.<br />

Gadian T. 1975. Carcinogens in industry, with special reference to dichlorobenzidine. Chemistry and<br />

Industry 4 October, pp.821-831.<br />

Gerarde HW and Gerarde DF. 1974. Industrial experience with 3,3’-dichlorobenzidine. An<br />

epidemiological study of chemical manufacturing plant. J Occup Med 16:322-344.<br />

Golub NI, Kolesnichencko TS, and Shabad LM. 1974. Blastomogenic action of some nitrogencontaining<br />

compounds in the progeny of experimental mice. Bjull Eksp Biol Med 68:83-87.<br />

250

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