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Male and female CD-1 mice and Sprague-Dawley CD rats (120/sex/group) were exposed to 0, 0.05<br />

or 0.15 ppm (0, 0.36 or 1.07 mg/m 3 ) industrial-grade TDI (approximately 80% 2,4 isomer, 20% 2,6<br />

isomer) by inhalation for 6 hours/day, 5 days/week, for 104 (mice), 108 (female rats) or 110 (male rats)<br />

weeks (Loeser, 1983). No treatment-induced increase in tumor incidence was noted in rats or mice.<br />

However, the rat histopathological evaluation was incomplete. Also, NTP (1986) noted that the<br />

exposure levels used corresponded to daily gavage doses of less than 1 mg/kg, and may not have been<br />

adequate doses to detect a potential carcinogenic response.<br />

IV.<br />

DERIVATION OF CANCER POTENCY<br />

Basis for Cancer Potency<br />

The NTP carcinogenicity study (1986) demonstrated that TDI induced tumors in several species (rats<br />

and mice), in both sexes in at least one of those species, at multiple sites. The male rat subcutaneous<br />

fibroma/fibrosarcoma tumor data was chosen as the basis of a cancer potency factor because it was the<br />

most sensitive endpoint in the most sensitive of the responsive species and sexes tested.<br />

Methodology<br />

Expedited Proposition 65 methodology (with cross-route extrapolation) was used to derive a cancer<br />

potency factor. A unit risk factor was then calculated by <strong>OEHHA</strong>/ATES from the cancer potency<br />

factor using a reference human body weight of 70 kg and an inspiration rate of 20 m 3 /day.<br />

V. REFERENCES<br />

California Environmental Protection Agency (Cal/EPA) 1992. Expedited Cancer Potency Values and<br />

Proposed Regulatory Levels for Certain Proposition 65 Carcinogens. Office of Environmental Health<br />

Hazard Assessment, Reproductive and Cancer Hazard Assessment Section, Berkeley, CA.<br />

Gold L, Slone T, Backman G, Eisenberg S, Da Costa M, Wong M, Manley N and Ames B. 1990.<br />

Third chronological supplement to the Carcinogenic Potency Database; Standardized results of animal<br />

bioassays published through December 1986 and by the National Toxicology Program through June<br />

1987. Environ Health Perspect 84:215-285.<br />

Hazardous Substance Data Bank (HSDB) 1994. National Library of Medicine, Bethesda MD (CD-<br />

ROM Version). Micromedix, Inc., Denver CO, Edition 22.<br />

International Agency for Research on Cancer (IARC) 1985. Toluene diisocyanate. In: IARC<br />

Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man, Volume 39. IARC, Lyon,<br />

France, pp. 287-323.<br />

Loeser E. 1983. Long-term toxicity and carcinogenicity studies with 2,4/2,6-toluene diisocyanate<br />

(80/20) in rats and mice. Toxicol Lett 15:71-81.<br />

517

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