Cereal Chem. 73 (5):605-612  |  VIEW ARTICLE

Analytical Techniques and Instrumentation

Analysis of Organophosphate, Pyrethroid, and Methoprene Residues in Wheat End Products and Milling Fractions by Immunoassay.

John H. Skerritt (1), Simone L. Guihot (2), Amanda S. Hill (1), Jim Desmarchelier (3), and Peter J. Gore (4). (1) CSIRO, Division of Plant Industry, GPO Box 1600, Canberra ACT 2601 Australia. Fax: + 61 6 246 5351. E-mail: <skerritt@pican.pi.csiro.au> (2) CSIRO, Division of Plant Industry, PO Box 7, North Ryde NSW 2113 Australia. (3) CSIRO, Stored Grains Research Laboratory, GPO Box 1700, Canberra, ACT 2601 Australia. (4) Bread Research Institute of Australia Incorporated, PO Box 7, North Ryde, NSW 2113 Australia. Current address: Cereform, 74-76 Redfern St, Wetherill Park, NSW 2164 Australia. Accepted June 27, 1996. Copyright 1996 by the American Association of Cereal Chemists, Inc. 

Wheat grain was spiked with five levels of three grain protectant mixtures, aged, then milled and further processed into a wide range of end products including seven types of bread and noodles. Enzyme-immunoassay methods for quantitation of residues of three organophosphate (fenitrothion, chlorpyrifos-methyl, and pirimphos-methyl), two synthetic pyrethroid (bioresmethrin, permethrin) grain protectants and an insect growth regulator (methoprene) were applied to the analysis of both the milling fractions and the end products. Three parameters were investigated: 1) potential matrix interferences obtained using a simple methanol extraction protocol; 2) a comparison of data obtained using the immunoassay and conventional instrumental methods (gas-liquid chromatography or high-performance liquid chromatography); and 3) changes in the residue levels during milling and processing. Where matrix interference did occur, it was typically manifested as a decrease in assay sensitivity in the presence of the extract of the sample under study. However, methanol extraction of residues gave relatively few matrix interferences in the case of organophosphates, and matrix effects were seen in only some of the pyrethroid assays. The simplest approach to obtaining accurate results, when matrix effects were present, was to prepare the assay standards in an extract of a pesticide-free sample of the matrix under study. Generally, there was a close relationship between residue levels as measured by immunoassay and by instrumental analysis. The extent of residues in different milling fractions and persistence in 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 products prepared from high-extraction-rate flours contained higher levels of pesticide, while white noodles (low-extraction-rate flour) and yellow noodles (alkali treated) contained low levels. Although the application rates used are lower, a greater proportion of pyrethroids, especially permethrin, were retained after milling and subsequent processing, compared with that of the organophosphates.