Reproductive and Cancer Hazard Assessment Branch Office of Environmental Health Hazard Assessment (OEHHA) California Environmental Protection Agency

The human cancer potency of chlorothalonil was estimated and used to calculate a “No Significant Risk Level ” (NSRL). The human cancer potency was estimated from dose-response data for multiple treatment-related tumor sites in male Fischer 344 rats exposed via their feed (Wilson and Killeen, 1989). An overall estimate of cancer potency associated with all treatment-related renal and forestomach tumors observed in the study was derived using a multisite statistical approach. The potency derivation takes into account differences in body size between humans and experimental animals. The human cancer potency estimate for chlorothalonil is 0.017 (mg/kg-day)-1. The Proposition 65 NSRL is defined in regulation as the daily intake level posing a 10-5 lifetime risk of cancer. The NSRL for chlorothalonil is calculated to be 41 g/day