mechanism (NRC 1987), any residue consumed can produce a statistical increase in lifetime dietary cancer risk.

Population subgroups differ in exposures to residues. Infants and children, for example, can receive higher exposures to pesticides that occur regularly as residues on such foods as apples, bananas, and pears because they consume more of these foods than adults and because they are smaller than adults. Their exposure to a pesticide in these foods is higher, on a bodyweight basis, than adults' (NRC 1993). The higher exposure, combined with the greater susceptibility of infants and children to some pesticides, can increase risks for these population subgroups.

People can be exposed through water or air or by dermal contact, in addition to food intake. Thus, their total, or aggregate, exposure can be considerably higher than their exposure via food intake. Exposure can be to several chemical residues simultaneously because some commodities are treated with more than one pesticide and because people consume many foods, any or all of which can contain residues. The effect of these cumulative residues and whether they act independently of each other or in an additive or synergistic manner, are subjects of active debate.

Other acute or chronic effects in people can be associated with residues in food, particularly in the context of illegal use of pesticides. Although aldicarb is still used legally on some food crops, thousands of people in the western United States became ill in 1985, some seriously, from consuming watermelons contaminated by the illegal use of this insecticide. Although random, composite sampling might show the remaining residues to be well within tolerance, there is some concern that individual samples or other commodity units could contain above-tolerance, possibly harmful residues (NRC 1993). Suspicions regarding potential teratogenic, neurotoxic, or hormone-disrupting effects also exist for some chemicals or residue mixtures; these are additional subjects of current research and public interest.

The concentration of pesticide residues in foods and the frequency with which they occur have decreased substantially in recent years. Data on pesticide residues in foods are generally available from field trials conducted by the registrant, monitoring programs of FDA and state agencies, and marketbasket surveys of FDA and USDA. Marketbasket surveys—such as FDA's Total Diet Study, in which foods purchased from supermarkets and prepared for consumption are analyzed—provide perhaps the best record of dietary intake, although the data are few. Marketbasket surveys support the idea that, generally, very low exposure to pesticide residues occurs through foods in the United States.

In part, the low exposure is due to the effects of commercial processing and food preparation (NRC 1993, Elkins 1989, Gelardi and Mountford 1993). The decline in food residues has occurred in large part, however,

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