Two quality assurance measures for pesticide analysis of wellwater: degradation in storage and GC/ELISA comparison
1996
Newman, J.K. | Glanville, T.D. | Baker, J.L.
At the request of Environmental Protection Agency (EPA) project coordinators, two special quality assurance components were included in a study of herbicides in rural wells in Iowa. Since the study involved daily sampling of 88 rural wells for a period of four to five weeks, it was anticipated that samples would be in refrigerated storage for up to eight weeks during which microbial and chemical activity could lead to analyte loss. The sample degradation study reported here was conducted to insure that water samples containing three herbicides (atrazine, alachlor, and metolachlor) did not undergo excessive losses during storage. Results indicate no reduction in pesticide concentrations in six refrigerated water samples analyzed weekly during an eight-week storage period. Due to budget and time limitations, the rural well-water study employed enzyme-linked immunosorbent assay (ELISA) techniques to determine atrazine, alachlor, and metolachlor concentrations in well-water samples. Since ELISA techniques generally are considered to be less accurate than the more costly gas chromatography (GC) technique, a GC/ELISA comparison study was designed to evaluate the accuracy of the water quality data from this study. Results of the GC/ELISA comparison show that the ELISA method may over-estimate pesticide concentrations or register a positive detection for a chemical that is not present. Based on results of this study and information from the ELISA test kit manufacturers, it is believed that ELISA results for this study were affected by cross-reactive parent compounds and/or metabolites. Deethylatrazine and prometon were identified as compounds that may have cross-reacted with the antibody of the atrazine test kit.
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