Pesticide discharges from irrigated agriculture in the Murray irrigation area, New South Wales, Australia

Pesticide discharges were monitored in a drainage system from the Murray Irrigation Area in south-western New South Wales using surface water sampling and gas chromatography/mass spectrometry (GC/MS) and other chromatography-based analyses. The drainage system monitored (~90 km long) included an artificial drain, natural creek and river during the irrigation season, and the drain and creek during the non-irrigation season. During the irrigation season, enzyme-linked immuno-sorbent assay (ELISA) for molinate and passive samplers containing 2,2,4-trimethylpentane (TRIMPS) were also used to assess their relative merits in measuring and monitoring pesticide discharges.

A wide range of pesticides were analysed, but during the irrigation season, only molinate and thiobencarb were frequently detected in the drain, associated with irrigated rice crops. These pesticides were also detected at the most upstream site of the receiving creek but not further downstream. During the non-irrigation season, atrazine and simazine were often detected in the drain, while dimethoate and glyphosate were occasionally detected.

During the irrigation season, the passive samplers detected thiobencarb that was not detected from surface water samples. ELISA was regarded as a useful screening method for molinate, although the method showed higher concentrations of molinate than GC/MS analysis.