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Xenobiotics are chemical substances that are foreign to the biological system. They include naturally occurring compounds, drugs, and environmental agents (Mondofacto online medical dictionary at www.mondofacto.com).The classes of xenobiotics include: pesticides, polyaromatic hydrocarbons (PAHs), polychlorinated aromatics, solvents, hydrocarbons, and others (surfactants, silicones, and plastics). Xenobiotics levels in soils are generally low (less than 100 ppm) unless they are concentrated by application as in the case of pesticides, by spills or by waste disposal. They can occur in soils in solid, dissolved and gaseous phases and all undergo microbial and abiotic (chemical) transformations (Logan, 2000). Photo source: www.cleanwaterfund.com Pesticides are the most important xenobiotic pollutants because of their widespread use in agriculture. In many developing countries, unregulated use of pesticides by poor farmers contributes not only to environmental pollution but to health probl