Experimental approach for pesticide mobility studies in the unsaturated zone

An experimental approach for pesticide mobility studies in the soil environment has been developed, based on three main aspects: 1) the development of analytical procedures suitable for unsaturated zone pesticide monitoring; 2) adsorption studies; 3) controlled application of pesticides to two experimental sites and subsequent analysis of soil and water samples. Four pesticides have been selected to perform this study: two herbicides (atrazine and metribuzin) and two organophosphorus insecticides (fenamiphos and chlorpyrifos). Soil and water samples spiked at different levels with pesticides were used to validate the analytical procedures by obtaining recoveries and coefficients of variation. Extraction procedures for water samples included: liquid-liquid extraction (conventional and micro scale) and solid phase extraction using C-18 cartridges and elution with ethyl acetate. Detection limits for water sample extraction using either liquid-liquid extraction or solid phase extraction were similar and ranged between 0.02 and 0.3 mu g l(-1), while for the liquid-liquid microextraction minimum detectable concentration was in the range of 1-10 mu g l(-1)) Extraction of soil samples was carried out with acetone, followed by two different clean-up procedures based on liquid-liquid partition and solid phase extraction with C-18 Cartridges (detection limits between 0.3 and 0.6 ng g(-1)). Results obtained for adsorption studies predicted that atrazine and metribuzin were probable leachers while the oganophosphorus pesticides studied should be considered as improbable leachers. This agreed completely with the mobility results obtained in experimental plot experiments.