ENZYMATIC BINDING OF PESTICIDE DEGRADATION PRODUCTS TO SOIL ORGANIC-MATTER AND THEIR POSSIBLE RELEASE

Many pesticides are hydrolyzed or otherwise transformed to phenol or aromatic amine intermediates. These intermediates are frequently incorporated into humic material through covalent binding. A reaction causing this binding is oxidative coupling catalyzed by oxidoreductive enzymes or abiotic agents. The reaction forms free radicals which are easily observed if pesticide intermediates are substituted phenols or anilines. The free radicals bind to reactive groups of humic substances or polymerize to become part of humus. The chemical linkages formed are quite stable and resistant. Nevertheless, the question arises to what extent the bound pesticide residues resist subsequent release during microbial or chemical attack. Our investigation with chlorinated phenols showed that the release of these xenobiotics is very slow and the released compounds are further degraded by microorganisms. Therefore, it appears that pesticides bound to humus usually do not present a hazard to the environment.