lites or breakdown products; decomposition products can be toxic and so need to be considered when dietary exposures are being calculated.
The occurrence and concentrations of pesticide residues in foods are monitored by several organizations (OTA 1988). USDA annually performs one of the most important surveys of fresh and processed fruit, grain, vegetables, and milk in the Pesticide Data Program as part of its efforts to meet the mandates of the FQPA. This effort includes collecting data on pesticide residues in foods most likely to be consumed by infants and children. FDA monitors residues in crops and other foods, harvested in and imported into the United States except meat, milk, and eggs, which fall under the purview of USDA. Several states, including California, Florida, and Texas, conduct random monitoring of residues in foods. And several food industries, most notably those dealing with infant food or such high-value products as wine and some packaged and canned foods, analyze food ingredients for pesticide residues.
The percentage of food that tests positive for pesticide residues is usually 20% or less for all pesticides (Archibald and Winter 1990). The frequency varies widely with the pesticide and the food commodity. For example, ethylene bisdithiocarbamate (EBDC) fungicides were found in 49 of 124 samples of succulent garden-variety peas but in only four of 100 samples of bananas (NRC 1993). Chlorpyrifos was found in 116 of 968 samples of fresh apples but in only nine of 751 samples of succulent peas (NRC 1993). The differences are in part a result of the specifics of registration (chlorpyrifos is registered for use on apples but not on succulent peas) and of the percentage of acreage treated even when registration and a tolerance exists for a chemical-commodity combination.
When residues are detected, they rarely exceed established tolerance limits. Of all FDA surveillance samples, both domestic and imported, 3% or fewer were found to be in violation (Archibald and Winter 1990). Violations are very rare because tolerances are set to take into account the maximal residue expected at harvest when the pesticide is used according to its label. Violations also occur when a residue is found on a commodity for which there is no registration for the pesticide found—often the result of illegal use or inadvertent residue contamination.
The concern over pesticide residues in foods has many dimensions. Some pesticides, such as benomyl and EBDCs, or their metabolites (ethylene thiourea-ETU is a metabolite of EBDC) are animal carcinogens or suspected carcinogens (NRC 1987, Winter 1992). Their presence in foods can increase the risk of death due to cancer. Risk is proportionate to the frequency with which a residue is encountered, the concentration of the residue, and the frequency of consumption of foods containing the residue. But because carcinogens do not appear to act through a threshold