ANALYSIS OF ORGANOPHOSPHATE, PYRETHROID, AND METHOPRENE RESIDUES IN WHEAT END-PRODUCTS AND MILLING FRACTIONS BY IMMUNOASSAY

Wheat grain was spiked with five levels of three grain protectant mixt ures, aged, then milled and further processed into a wide range of end products including seven types of bread and noodles. Enzyme-immunoass ay methods for quantitation of residues of three organophosphate (feni trothion, chlorpyrifos-methyl, and pirimphos-methyl), two synthetic py rethroid (bioresmethrin, permethrin) grain protectants and an insect g rowth regulator (methoprene) were applied to the analysis of both the milling fractions and the end products. Three parameters were investig ated: 1) potential matrix interferences obtained using a simple methan ol extraction protocol; 2) a comparison of data obtained using the imm unoassay and conventional instrumental methods (gas-liquid chromatogra phy or high-performance liquid chromatography); and 3) changes in the residue levels during milling and processing. Where matrix interferenc e did occur, it was typically manifested as a decrease in assay sensit ivity in the presence of the extract of the sample under study. Howeve r, methanol extraction of residues gave relatively few matrix interfer ences in the case of organophosphates, and matrix effects were seen in only some of the pyrethroid assays. The simplest approach to obtainin g accurate results, when matrix effects were present, was to prepare t he assay standards in an extract of a pesticide-free sample of the mat rix under study. Generally, there was a close relationship between res idue levels as measured by immunoassay and by instrumental analysis. T he extent of residues in different milling fractions and persistence i n different products varied with the compound and the product. As the milling extraction rate increased, the levels of residue in the flour, relative to the application rate, were greater. Similarly, baked prod ucts prepared from high-extraction-rate flours contained higher levels of pesticide, while white noodles (low extraction-rate flour) and yel low noodles (alkali treated) contained low levels. Although the applic ation rates used are lower, a greater proportion of pyrethroids, espec ially permethrin, were retained after milling and subsequent processin g, compared with that of the organophosphates.