IMMUNOASSAY DETECTION OF HERBICIDE RESIDUES IN CORN

Immunoassay detection kits were used to detect herbicide residues in s piked corn samples. Five herbicide compounds (atrazine, alachlor [Lass o], metolachlor [Dual], cyanazine [Bladex], and 2,4-dichlorophenoxy ac etic acid [2,4-D]) commonly used by corn producers were selected as an alytes. Selection was based on a survey of 200 Iowa Corn Grower Associ ation members. Commercial test kits for water analysis for these compo unds were available from Ohmicron Corporation, Newtown, PA. Two extrac tion methods, blender and heated shaker, were compared for efficiency of herbicide recovery at three spike levels. The blender method yielde d recoveries of 80-100% of herbicide spike in the immunoassay for all compounds. Recoveries from the heated shaker method were comparable fo r four of the five compounds. Low detection limits for the immunoassay in corn were 20 ppb, with greater variability near the low end of the calibration. Variability decreased with increasing levels of herbicid e spike. Recoveries on selected spiked samples were confirmed by tradi tional detection methods. Blank adjustments were made to compensate fo r the interferences caused by the corn. Iowa farmers provided 200 corn samples and accompanying two-year herbicide usage history. These samp les were assayed for the five compounds, using the immunoassay test ki ts. Herbicide usage patterns were close to those reported in Iowa and Illinois industry data. No samples tested positive for atrazine, alach lor, metolachlor, or cyanazine. There were two positive, above-toleran ce results, not confirmed by chromatography, for 2,4-D. The immunoassa y required 0.5 hr of labor per sample in addition to the cost of the k it.