Evaluation of a novel malathion immunoassay for groundwater and surface water analysis.

Malathion is an organophosphorus insecticide commonly used in crops and indoor applications. Negative effects of malathion on human health and ecosystems are of growing concern. In this work, novel malathion haptens are synthesized to develop an ELISA screening method. The immunoassay is based on a conjugate-coated format and shows a limit of detection of 0.11 ng/mL, an IC50 of 1.58 ng/mL, a dynamic range between 0.23 and 10.94 ng/ mL, and a cross-reactivity of <2% with structurally related compounds. The developed ELISA has been used to quantify malathion in groundwater and surface water samples. The good recoveries achieved and the agreement with those given by the GC-MS reference method indicate the potential of the assay for environmental monitoring of malathion in natural waters without purification or preconcentration steps. The effect of dissolved organic matter (humic acids) on the ELISA was evaluated, resulting in the conclusion that the immunoassay can be successfully performed in surface water samples with a humic acid content up to 10 mg/L, without sample pretreatment. Samples with a high humic acid content can be analyzed through ELISA after solid-phase extraction, eluting with acetone or acetonitrile.