ATRAZINE PERSISTENCE AND TOXICITY IN 2 IRRIGATED SOILS OF AUSTRALIA

The persistence of atrazine in two contrasting irrigated soils from the Riverine Plain of south-eastern Australia was measured in the laboratory at three constant temperatures. Particularly at lower temperatures atrazine was more persistent, by an order of magnitude, than reported for soils overseas; but in two successive field experiments, encompassing both surface and incorporated applications of atrazine in the heavier soil, residues measured after about 7 months were within the range expected from the literature. The measured residues were 2-6 times smaller than predicted using a simulation model, probably reflecting volatilization and other losses which are not included in the model, but which are expected to be substantial at the extremely high soil surface temperatures observed in the field. Comparative measurements of aged residues in the heavy clay soil showed higher results from chemical analysis of acetonitrile-water soil extracts than by in situ glasshouse bioassay using oats and turnips, demonstrating that only one third of the extractable residue was available to crops. Comparison of soil-based and hydroponic assay using soybeans showed that this soil reduced the effective atrazine concentration in solution by at least 16-fold, but sensitive crops could still be damaged when grown in rotation after tolerant crops, or if irrigated with contaminated water.