Modelling the bioavailability of pesticides to soil-dwelling organisms

Present knowledge of the effects of pesticides on terrestrial organisms is based on laboratory, semi-field and field investigations. The results found in various experiments differs probably owing to variations in test conditions. A comprehensive model based on chemical and physical pesticide properties and biotic and abiotic factors has been developed. The model is able to predict the exposure of pesticides to soil-dwelling organisms under different test conditions, e.g. different soil types. If the exposure is related to the toxicity of the pesticides, the model is able to predict the short-term mortality of pesticides on soil-dwelling beetles (Coleopterans) which are mainly used as examples in the model development. The cumulative body burden is used as a measure of the hazard. The model involves four routes of pesticide uptake. For every route, a time-dependent uptake is calculated. Considering model prediction, the most important route is uptake from the soil; it is also the most difficult to estimate. This is due primarily to large variations in pesticide parameters and soil properties. Uptake through food may add significantly to the total pesticide uptake, but it is maybe overestimated. Topical exposure may cause high mortality rates, but this depends on the toxicity of the pesticides and the presence on the number of beetles on the soil surface at the time of pesticide application. Uptake of pesticides through the respiratory system is negligible. The soil model constructs fairly well dose-response curves for four pesticides, where toxicity data were obtained on different soil types and different times of release of the beetles. The outcome of the model calculations may be used when extrapolating toxicity data from laboratory to field conditions.