Physicochemical properties are set in relation to the transfer among environmental compartments, transport and environmental fate of chemical pollutants. The mechanism underlying Biomagnification of chemical contaminants along the food chain will be studied and put in relation to the properties possessed by the compounds, distinguishing between bioaccumulation and bioconcentration. Hydrolysis and photodegradation, the two main mechanisms of abiotic degradation of chemical pollutants in the environment are reviewed. Environmental biodegradation as a determining phenomenon of final destination of chemical contaminants and essential to the survival of ecosystems in the current circumstances is studied. Biodegradation is explained as the attempt by environmental microorganisms of using organic pollutants as substrates for their own growth. Major enzymatic reactions involved in the biodegradation of aliphatic, alicyclic and aromatic compounds, both under aerobic and anaerobic conditions, as well as reactions with polyhalogenated compounds are described. Variables affecting environmental biodegradation of xenobiotics are discussed distinguishing between those dependent on environmental factors, with applications in the bioremediation of polluted sites, and those depending on the chemical structure of the compound, that provide the key for the synthesis of more readily biodegradable compounds.