PESTICIDE-RESIDUES IN FOOD - INVESTIGATION OF DISPARITIES IN CANCER RISK ESTIMATES

Much of the public perceives that exposure to synthetic pesticide resi dues in the diet is a major cause of cancer. The National Research Cou ncil (NRC), in a 1987 report, Regulating Pesticides in Food: The Delan ey Paradox, evaluated cancer risks for 29 pesticides that are rodent c arcinogens and estimated that the risks for 23 were greater than one-i n-a-million. In contrast, our group has ranked possible carcinogenic h azards from a variety of human exposures to rodent carcinogens using t he HERP (Human Exposure/Rodent Potency) index, and found that dietary residues of synthetic pesticides ranked low. This paper evaluates the disparities in these analyses by examining the two components of risk assessment: carcinogenic potency in rodents and human exposure. Potenc y estimates based on rodent bioassay data are shown to be similar whet her calculated, as in the NRC report, as the regulatory q(1) or as TD 50. In contrast, estimates of dietary exposure to residues of syntheti c pesticides vary enormously, depending on whether they are based on t he Theoretical Maximum Residue Contribution (TMRC) calculated by the E nvironmental Protection Agency vs. the average dietary residues measur ed by the Food and Drug Administration in the Total Diet Study (TDS). The TMRC is the theoretical maximum human exposure anticipated under t he most severe field application conditions, which are far greater tha n dietary residues measured in the TDS. Several independent exposure s tudies suggest that the FDA dietary residues are reasonable estimates of average human exposures, whereas TMRC values are large overestimate s. Using standard methodology and measured dietary residues in the TDS , the estimate of excess cancer risk from average lifetime exposure to synthetic pesticide residues in the diet appears to be less than one- in-a-million for each of the ten pesticides for which adequate data we re available. Published by Elsevier Science Ireland Ltd.