Fate of herbicides influenced by biotic and abiotic interactions

The interactions between 2,4-D and simazine with inorganic and organic soil colloids affected by adsorption (abiotic) and enzymatic mechanisms (biotic ) were investigated. Complex model systems which closely simulate those enc ountered in soils [i.e. pure montmorillonite, montmorillonite covered by di fferent amounts of OH-Al species (chlorite-like complexes)], were used as a dsorbents. 2,4-D gave a negligible adsorption on pure montmorillonite, wher eas it was significantly adsorbed on chlorite-like complexes. The larger th e OH-Al amounts on clay surfaces, the greater the quantity of 2,4-D adsorbe d. An opposite behaviour was observed with simazine, which adsorbed much mo re on montmorillonite than on chlorite-like complexes. A well characterised laccase from the fungal strain Cerrena unicolor was used as biotic catalys t. The enzyme displayed a lower ability to oxidise 2,4-D and simazine where as it was extremely efficient in the oxidation of 2,4-DCP (a derivative of 2,4-D) and catechol. The presence of soil colloids or reactive co-substrate s differently influenced the enzymatic transformation of 2,4-DCP. The resul ts obtained in this study provided useful information for predicting the be haviour of a xenobiotic substance when entered into soil. (C) 1999 Elsevier Science Ltd. All rights reserved.