Influence of microbial and enzymatic activities on immobilisation of xenobiotics in soil organo-clay complexes

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Organo-clay complexes are a major sink of non-extractable residues in soil. Although it is known that this incorporation is dominantly assisted by microbial activity, the exact mechanism remains unclear. The competition of extracellular enzyme activity versus contribution of living biomass is under discussion. Therefore we will study the role and participation of microorganisms as well as stabilized extracellular enzymes in the covalent immobilization process of two xenobiotics on organo-clay particles in soil, i.e. the endocrine disrupting compound 353-nonylphenol (p-353-NP) and the fungicide metalaxyl.Three systems are investigated: (a) whole soil, (b) native organo-clay complexes and (c) model organo-clay complexes, both in sterilized and non-sterilized form. This strategy will allow the separation of effects from living micororganisms from those of extracellular enzymes and enables the detailed characterisation of microbial assisted bonding processes. NER formation will be followed by radioanalyses using 14C-xenobiotics and quantitative, enantioselective as well as compound specific isotope analyses using unlabelled substances. Further on the potential of specific enzymes (peroxidase, phenoloxidase) for NER formation will be tested.We will thus test the hypothesis that extracellular enzyme activities are the main driving force for covalent immobilization of xenobiotics to organo-clay complexes in soils.