Detection of chlorpyrifos-ethyl (Dursban) and its metabolites in urine samples using immunoassays with confirmation by gas chromatography/mass spectrometry

Abstract

Chlorpyrifos-ethyl (Dursban) belongs to the organophosphate class of pesticides. Many organophosphates, such as parathion and chlordane, are highly toxic and have restricted usage. Others, including chlorpyrifos-ethyl, are widely used for domestic and agricultural purposes because of their relatively low toxicity. Exposure to chlorpyrifos-ethyl is commonly determined by measuring cholinesterase inhibition. This method requires blood. sample analysis via gas chromatography/mass spectrometry (GC/MS), and can be expensive and time consuming. Immunoassay techniques have been developed for measuring chlorpyrifos-ethyl concentrations in water. Compared to conventional methodology, these new techniques are economical, rapid, and statistically equivalent to GC/MS results. This study attempted to quantify the amount of chlorpyrifos-ethyl in urine samples using the two-step indirect competitive assay form of Enzyme Linked Immunoabsorbent Assay (cELISA), with confirmation by GC/MS. The selected cELISA (Millipores EnviroGard chlorpyrifos-ethyl plate kit) is a quantitative laboratory test traditionally used to detect chlorpyrifos-ethyl in water samples. Even though the parent compound is metabolized before being excreted in urine, the urinary traces of chlorpyrifos-ethyl that are present should have been sufficient for the purposes of this study. The cELISA was selected solely because it detects chlorpyrifos-ethyl at 0.08 ppb. It was also selected because it detects the primary metabolite 3,5,6-TCP, which was expected in urine, at 85 ppb. While the metabolite's detection limit is not as desirable as the parent compounds' detection limit, it is still acceptable. Chlorpyrifos-ethyl was detected in a few samples with the immunoassay. However, traditional GC/MS techniques failed to detect this pesticide in the same samples. No correlation was established between the two methods. Therefore, it is not yet possible to recommend this cELISA as a reliable method for detection of chlorpyrifos-ethyl in urine.