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The Future Role of Pesticides in US Agriculture
All exposures to pesticides, dietary and nondietary, should be considered in evaluating risks to infants and children. Exposure distributions, rather than single-point data, should be used to characterize the likelihood of exposure to different concentrations of pesticide residues.
Virtually all of the recommendations of the committee were incorporated in some way in FQPA, primarily in its amendments to FFDCA. These included:
Mandated consideration of the special sensitivity and exposure of children to pesticides
Requirement of an explicit determination that tolerances are safe for children.
Requirement of an additional safety factor of up to 10 based on available information and evidence, to account for the uncertainty of exposures and sensitivities of children.
Requirement of consideration of exposure to all other pesticides with a common mechanism of toxicity in the setting of allowable residue concentrations.
The conventional method of calculating acceptable daily intake, or reference dose, (RfD) (Barnes and Dourson 1988) for pesticides included use of an experimentally determined no-observed-adverse-effect-level (NOAEL) derived from long-term animal toxicity tests. This is coupled with an uncertainty factor (or safety factor) for extrapolating from animals to humans and across the human population. The latter was generally 10 for intraspecies differences (other humans and animals) and 10 for interspecific or individual differences (Ui) Differences in susceptibility among species were assigned an additional uncertainty factor of 10 (Us). A further uncertainty factor of 10 could be assigned for studies that encompassed less than a full life span (Ut), and a modifying factor (M, ranging from 0.1 to 10) could be used to account for issues related to the quality of the studies. Consequently RfD = NOAEL ÷ (Ui × Us × Ut × M).
FQPA adjusted this “acceptable risk” for each pesticide by recommending an expanded uncertainty factor, up to 1,000. It also requires that all chemicals with a common mechanism of toxicity be included in calculating the RfD for a single chemical. For organophosphates, for example, calculating an RfD for one member must include the possibility that other organophosphates might co-occur in food or drinking water. The FQPA requirement that all exposure (dietary, home use, water, air) be considered in setting an RfD for a single chemical still further restricts the RfD for a given chemical.
The concept of a “risk cup” was developed to illustrate the new regu-