Organic Pollutants Associated with Macromolecular Soil Organic Matter and the Formation of Bound Residues

Abstract

All anthropogenic organic chemicals form non-extractable residues to some extent after entering soils. This well known phenomenon has been studied intensively in the field of soil agrochemistry. Similar processes have been observed during the bioremediation of oil-contaminated soils. Thus, the residue formation of toxic and carcinogenic polycyclic aromatic hydrocarbons is of particular concern. Beside mineralisation by microbial activity, the formation of non-extractable residues is a major sink for anthropogenic pollutants in soils. Microbial activity often stimulates the formation of bound residues. On a molecular scale, bound residue formation is suggested to be a covalent binding of xenobiotic substances and their metabolites to macromolecular natural organic matter in soils and sediments. When this binding occurs, the xenobiotic substance loses its chemical identity. A strong reduction of the bioavailability of xenobiotic carbon is one major consequence of bound residue formation in soils. In this overview we will discuss the present state and new trends in the field of bound residue research regarding the application of isotopically labeled tracer substances. Carbon budgets are emphasized to study the fate of isotopically labeled PAH in soils, including bound residue formation.