Reentry field data and conclusions.

Abstract

A review of the reported foliar residue data has revealed a number of deficiencies in the reentry intervals currently regulated, in particular, by the EPA and some by California. Deficiencies were also identified in the available information necessary to recommend better reentry intervals. Information regarding the frequency of exposure for individual or groups of harvesters is the most fundamental deficiency. It is needed to define a more realistic chronic criterion of allowable daily cholinesterase inhibition without cumulative symptoms. The second criterion of preventing acute overexposure is more readily defined. For the purposes of this study, the criteria of 4% mean daily inhibition and 50% acute inhibition were chosen as acceptable. Based on these criteria, the available data, and by using the unified field model assessment as the basis for comparison (Table 9), EPA reentry intervals for nine insecticides in Table 4 appear inadequate (i.e., not within the range of the model recommendations); 10 are adequate; and only one appears excessive as summarized in Table 10. A similar comparison of California's reentry intervals indicates only two may be inadequate or marginal; 13 are adequate; and five may be excessive. Although these conclusions are based on a considerable amount of residue data, the data are not equally distributed among all pesticides nor has the model been confirmed in all the cropping and harvest conditions examined. However, the model has been developed under realistic field tests, most of its premises have been confirmed in a limited number of tests, and its simulated predictions appear to parallel experience in California where pesticide use and decay conditions may have been most severe but recently well scrutinized. The model's recommendations largely substantiate the regulations developed in California. However, its conclusions definitely suggest that improved levels of protection are needed in other regions. Future reentry intervals will require more comprehensive residue data. The toxicities of detectable metabolites for a few insecticides will need to be determined. More crop residue dosing coefficients are also needed for manually harvested crops. These data must be interpreted in terms of the potential both for acute poisoning from variable residues and for chronic poisoning from repeated exposure to more consistent residues. Surveys of the temporal exposure patterns of harvesters or crews of harvesters are vital to assess the cumulative effects and set the most appropriate chronic cholinesterase response limits. While we await further data, there is sufficient information now to justify longer reentry intervals to protect harvesters nationally.