DEVELOPMENT AND APPLICATION OF LABORATORY AND FIELD IMMUNOASSAYS FOR CHLORPYRIFOS IN WATER AND SOIL MATRICES

Two sensitive tests were developed for monitoring the environmental di ssipation of chlorpyrifos, using a high-affinity polyclonal antibody i mmobilized onto microwells and polystyrene tubes. The microwell assay, which required 90-120 min to perform, was designed for laboratory use and could detect 0.05-0.07 ppb of chlorpyrifos (85% B-0), with 50% in hibition of antibody binding (50% B-0) at 0.2-0.6 ppb of chlorpyrifos. The tube assay was designed for field use, required 15-20 minutes to perform, and had a lower limit of detection for chlorpyrifos of 0.15 p pb and 50% inhibition of antibody binding at 0.8-1.6 ppb. The assays w ere thus sufficiently sensitive for direct analysis of chlorpyrifos in irrigation drainage water samples, after addition of phosphate buffer to 0.025 M to the sample to slow its hydrolysis. The assay was unaffe cted by several cations and anions that may be found in surface water. Performance of the assays was examined for three situations represent ing a wide range of incurred chlorpyrifos residue concentrations: trac e levels in irrigation drainage water, moderate levels in runoff from horticultural application, and high levels in soil following applicati on as a termiticide. These assays were applied to the analysis of surf ace water and soil. No cleanup was required for any matrix. Good corre lations were obtained between chlorpyrifos levels determined using the immunoassays and chlorpyrifos levels determined by gas chromatography -mass spectroscopy (GC-MS) or HPLC.