||Health Effects Research Lab., Research Triangle Park, NC. ;National Toxicology Program, Research Triangle Park, NC. ;PATHCO, Inc., Research Triangle Park, NC.
Approximately 41% (26/63) of the pesticides evaluated in the chronic toxicity and carcinogenicity studies of the National Toxicology Program (NTP) showed varying degrees of carcinogenicity. Since those chemicals nominated to the NTP for carcinogenicity studies usually represent a sampling of potentially 'problem' chemicals, this ratio does not implicate the actual percentage of carcinogenic chemicals among all pesticides. In general, results from epidemiological studies are of limited value in prevention and have been done on few pesticides. To assess potential risks of chemicals to humans, extrapolation of the findings in laboratory animals to possible health effects in humans is inevitable. Several important biological issues must be considered in such a process; these include extrapolation between doses, species (including strain and sex), routes of administration and exposure regimens (e.g., intermittent vs.constant rate). Any imperfection in such a process (e.g., hazard identification and risk assessment of any given chemical or other agent) must be taken into consideration during extrapolation.