• When less than 100% of a given crop is treated with a particular pesticide, consideration might be given to adjusting exposure estimates according to the percentage of crop acreage treated. This adjustment can result in substantial reductions in estimates of exposure. This adjustment will be appropriate when the percentage of the crop treated is similar in different regions of the country, or when the crop is uniformly distributed throughout the country. Such adjustments should not be considered in the case of pesticides inducing acute toxic effects, since peak exposures are of importance in this case.

When these adjustments are used to adjust national data, they may result in averages that do not account for regional differences in pesticide use. It is therefore important that exposure estimates that have not been adjusted for acreage treated be presented and that such adjustments be critically examined.

The following recommendations were developed by the committee.

• Probability distributions based on actual data rather than simple summary statistics such as means or percentiles should be used to characterize human exposure to pesticide residues on food.

The advantage of using probability distributions rather than summary statistics to characterize exposure is that variation in individual food consumption patterns and residue levels in food are taken into account. This will require the collection of more detailed data on food consumption and residue levels as discussed in Chapters 5 and 6, respectively, but will provide more statistically robust estimates than the agency currently develops.

• The distribution of average daily exposure of individuals in the population of interest is recommended for use in chronic toxicity risk assessment; the distribution of individual daily exposures is recommended for evaluating acute toxic effects.

This recommendation is based on the committee's observation that chronic toxicity is typically related to long-term average exposure, whereas acute toxicity is more often mediated by peak exposures occurring within a short period, either over the course of a day or even during a single meal.

• If appropriately designed and conducted, surveillance studies of pesticide residues in food provide unbiased data on residue levels in food products. Field trials are also useful sources of information on pesticide residues in food. Such studies should be continued in order to expand the data base for evaluating dietary exposures to pesticides.