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Environmental fate of pesticides bound to soil components through abiotic and biotic mechanisms

Exploitable results

The use of pesticides for agricultural production practices has been increasing up to recent years. This indiscriminate utilization has led to both a dramatic improvement in production management and dangerous accumulation levels of these pollutants in all ecological departments of all parts of the Earth. In order to correctly apply these xenobiotics, to improve their effectiveness, and simultaneously to reduce their adverse pollutant effects on the environment, a thorough understanding of all the factors and processes which control the fate and movement of these chemicals in soil is required. Information on the nonbiological and biological transformation of pesticide-organo-mineral complexes as well as on the possible release, movement and fate of residues in soils is needed for a correct utilization of these agents. Advanced information on the processes and the factors that control and govern the fate of pesticides in the soil environment was achieved by defining and elucidating the mechanisms at each step of the processes, using model systems formed by interactions of pesticides with natural and synthetic supports. Most of the experiments were performed with only two clay-humic complexes. Synthetic model systems (clays, humics, and clay-humic complexes) were prepared, well characterized and used as supports in adsorption/desorption studies. Sorption/desorption of dichlorophenoxy acetic acid (2,4-D) and simazine on synthetic supports (clays, humics and clay-humic complexes) that simulate well those naturally existing in soil was defined. Results demonstrated that the nature and type of soil as well as the meteorological conditions have a dominant role in controlling the behaviour of pesticides in soil. The results have shown that clay-humic complexes have a dominant role in controlling the leaching and mobility of pesticides in soil. The mobility of both the herbicides was greatly influenced by the presence of humic substances in sorbing matrices. Simazine remained firmly bound to humic acids whereas 2,4-D showed the opposite behaviour. This herbicide bound more firmly to clays-humic complexes than simazine. Caution should be used in evaluating desorption of pesticides under natural conditions using the results from batch methods and/or those obtained with individual sorbing matrices. Dry cycles as well as precipitation pauses have an effect on the mobility of pesticides which is chemical and matrix dependent.

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