A Model for Enzymatic Binding of Pollutants in the Soil

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Abstract
Pollutants released into the environment may be bound to humic acid through abiotic or biologic processes whereby the formation of bound residues usually results in detoxification of the pollutant. Therefore, enhancing the binding of xenobiotic chemicals to humic material can serve as a means to reduce toxicity as well as migration of toxic compounds in the environment. Complex formation can occur by an oxidative coupling reaction leading to oligomeric and polymeric products. We intensively investigated the effect of phenoloxidases (peroxidases, tyrosinases, and laccases) on the binding of substituted phenols and aromatic amines to humus monomers as well as to humic substances. Based on a large number of isolated and identified cross-coupling products, we are able to elucidate the sites and mechanisms of binding and also to determine the efficiency of some coupling reactions. Copolymerization largely depends on the chemical reactivity of the substrates involved. Certain phenolic humus constituents, such as guaiacol or ferulic acid, are highly reactive in the presence of phenoloxidases. When one of these compounds was incubated together with a phenoloxidase with less or even non-reactive phenols, anilines or other chemicals, a synergistic reaction took place, resulting in increased formation of bound residues of these compounds.