Soil contamination from buried pesticides.

The extensive application of pesticides creates an environmental risk due to the toxic pesticide residues, identified in air, water, soil, foods and human tissues. (Diskith, 1991). Their disposal especially by burial, a method widely applied in the past, apparently contributes to the soil contamination. The most important classes of pesticides are organophosphorus and organochlorine compounds. Generally, these compounds are degraded in soil by microorganisms to derive energy, carbon and other nutrients for their growth and metabolism, increasing their population and thus affecting the transformation of plant nutrients, in soil (Bollag 1982). Some pesticides (particularly organochlorine compounds) were banned after evidence of their toxicity, persistence and bioaccumulation in the environment and their ability to concentrate in the food chain. Organophosphorous compounds are considered to degrade, either biologically or chemically, in plants, animals and soils, more rapidly depending on their formulation, method of application, climate and soil types and conditions (Khan 1980). Data on the environmental fate of pesticides are required, in order to determine the potential of a pesticide to reach groundwater, including information on its hydrolysis, photolysis, aquatic metabolism, leaching and field dissipation. Since the fate of pesticide residues are of great importance, they are currently detected by determination in various environmental matrices. The chromatographic techniques used for pesticide analysis require efficient isolation and preconcentration procedures (Barcelo 1991, Miliadis 1994). Traditional extraction methods are often inconvenient (time consuming and expensive) for sample analysis and faster and more effective techniques such as solid phase extraction (SPE) are applied (Zief and Kiser, 1990).