Leaching of oxidation products of aldicarb from greenhouse soils to water courses

When the insecticide/nematicide aldicarb was incubated in three greenhouse soils at 20°C, the transformation rates of the parent compound and its first oxidation product aldicarb-sulfoxide were high, while the amounts of aldoxycarb (=aldicarb-sulfone) remained low. The transformation and movement of aldicarb and its oxidation products in a simplified greenhouse-soil system were simulated with a computation model. When the highest transformation rates were introduced into the computations in combination with high irrigation rates, the computed leaching was only 0.006% of the dose, with a maximum concentration of 0.15g L^–1 in the tile-drain water. With lower transformation rates, the computed leaching was 1.39% of the dose with a maximum concentration of 21.0g L^–1, but in combination with a lower irrigation rate the leaching was computed to be much less. Water from drain pipes and pits was sampled in three greenhouses that had received regular applications of aldicarb: the concentrations measured by high performance liquid chromatography (HPLC) varied from less than 1g L^–1 to more than 30g L^–1. Most of the concentrations measured in water courses in an area with many greenhouses were low, but some were high, ranging up to 21g L^–1. Ways of reducing the discharge of the oxidation products of aldicarb from greenhouse soils to water courses are suggested.