Experimental approach for pesticide mobility studies in the unsaturated zone

An experimental approach for pesticide mobility studies in the soil environ ment 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 exper imental sites and subsequent analysis of soil and water samples. Four pesti cides have been selected to perform this study: two herbicides (atrazine an d metribuzin) and two organophosphorus insecticides (fenamiphos and chlorpy rifos). Soil and water samples spiked at different levels with pesticides were used to validate the analytical procedures by obtaining recoveries and coeffici ents of variation. Extraction procedures for water samples included: liquid -liquid extraction (conventional and micro scale) and solid phase extractio n using C-18 cartridges and elution with ethyl acetate. Detection limits fo r water sample extraction using either liquid-liquid extraction or solid ph ase extraction were similar and ranged between 0.02 and 0.3 mu g l(-1), whi le for the liquid-liquid microextraction minimum detectable concentration w as 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 li quid-liquid partition and solid phase extraction with C-18 Cartridges (dete ction limits between 0.3 and 0.6 ng g(-1)). Results obtained for adsorption studies predicted that atrazine and metribu zin were probable leachers while the oganophosphorus pesticides studied sho uld be considered as improbable leachers. This agreed completely with the m obility results obtained in experimental plot experiments.