Degradation of organic matter from black shales and charcoal by the wood-rotting fungus Schizophyllum commune and release of DOC and heavy metals in the aqueous phase

We investigated the degradation of refractory organic matter (OM) by the basidiomycete fungus Schizophyllum commune to understand the release of dissolved organic compounds, heavy metals and sulfur. The investigated OM consisted of: charcoal, the short time end product of high temperature wood alteration in the absence of oxygen and composed mainly of pure OM; and black shales composed of clay minerals, quartz, sulfides and OM formed geogenically in an abiotic long-term process. In both cases, the OM fraction contains mainly polyaromatic hydrocarbons. We investigated the degradation of these fractions by a wood-rotting basidiomycete, which is able to produce exoenzymes like peroxidases and laccases. These enzymes can perform radical reactions to oxidize OM (like lignin) and therefore hypothetically are able to degrade OM from charcoal and/or low grade metamorphic black shales. Release of new components into dissolved organic carbon (DOC) could be detected in both cases. The attack on OM in the case of black shales coincided with the release of the heavy metals Fe, Mn and Ni. By following sulfur concentrations throughout the experiment, it was shown that heavy metal release is not due to pyrite oxidation. Ground black shale and charcoal samples were inoculated with S. commune in a diluted minimal medium containing aspartic acid and glucose. The aqueous and solid phases were sampled after 1, 7, 28 and 84 days. DOC was measured as non purgeable carbon and characterized by size exclusion chromatography and UV detection. Carbon concentrations of the solid phase were determined by element analyses. After initial decrease of the DOC concentrations due to the degradation of the carbon source provided with the medium, DOC increased up to 80 mg/l after 84 days. Carbon decreased in the solid fraction confirming that this carbon was released as DOC by the fungus. The newly generated DOC formed larger agglomerations than the DOC of the growth medium. The investigation proved that the degradation of persistent carbon sources, such as charcoal and black shale, is accelerated by fungal activity. Consequently, the associated release of heavy metals is also accelerated by the fungus. Main products of the biological degradation processes were organic heavy metal complexes which can enter the environment.