Mineralization of 14C-labelled humic acids and of humic-acid bound 14C-xenobiotics by Phanerochaete chrysosporium

Abstract

Humic compounds are generally stabilized in soil against microbial decomposition by their complex polymer structure and their adsorption to the inorganic soil matrix. Also the great resistance to degradation of “bound” residues from plant protection agents is believed to be largely related to the incorporation of the parent chemical or its partial degradation products into humic polymers. Changes in the environment or in management practices, however, can lead to an enhanced degradation of both soil organic matter or “bound” residues. Obviously, these organic matter components then become available to microbes and soil organisms which degrade lignin are very likely involved in the degradation process. We determined to what extent P. chrysosporium, one of the most active ligninolytic fungi, could mineralize humic acids, “bound” components from xenobiotics in humic acids, phenolic model polymers and the free xenobiotic chemicals. For the investigations 14C-labelled humic acids, humic acids with 14C-labelled plant protection chemicals or model polymers from phenols together with 14C-constituents were utilized for degradation studies. After 18 d in culture solutions, the fungus released about 13–56% of the labelled C as CO 2 in most of the tests. Some of the free compounds appeared to be toxic to the fungus. High nutrient N-concentrations in the culture solutions tended to reduce decomposition rates.