ABSTRACT
This chapter presents an overview of the factors that determine the persistence of xenobiotics including the role of both abiotic and biotic reactions. Two essentially different processes determine the persistence of an organic compound in the aquatic environment. The processes are: abiotic reactions, and photochemical reactions. Biotic reactions is generally conceded that biotic reactions are of primary' significance in determining the fate and persistence of organic compounds in most natural aquatic ecosystems. Although chemical transformations in the atmosphere are peripheral to this discussion, these reactions should be kept in mind since their products may subsequently enter the aquatic and terrestrial environments. The products of incomplete combustion may be associated with particulate matter before their discharge into the atmosphere, and these may ultimately enter the aquatic and terrestrial environments in the form of precipitation and dry deposition. Photochemical reactions may be important especially in areas of high solar irradiation, or in aquatic systems containing ultraviolet absorbing humic and fulvic acids.
