Degradation of polychlorinated biphenyls by white‐rot fungi pleurotus ostreatus and trametes versicolor in a solid state system

An industrial PCB‐isomer mixture, made up mainly of tri‐ and tetra chlorinated biphenyls, were loaded on wood chips and incubated with Pleurotus ostreatus and Trametes versicolor. After only 5 weeks the PCB mixture was degraded more than 95%. Penta‐ and hexachlorbiphenyls are also found to be degradable by more than 50%, depending on their substitution pattern. Only 2,2’,4,4’,5,5'‐hexachlorbiphenyl (Ballschmiter No. 153) was resistant to degradation. Contaminant concentrations ranged from 100 ppm to 650 ppm for single isomers and 2500 ppm for all PCBs. Phanerochaete chrysosporium was not able to degrade any PCB except mono‐ and dichlorbiphenyl in a solid state system under normal oxygen levels.

Lignosulfonate, an inducer of lignolytic activity, had no effect on the degradation of PCBs with Pleurotus ostreatus or Trametes versicolor. Malt medium supported the growth of fungus and could also be replaced by potato pulp. An oxygen concentration of 10% inside the substrate combined with 10% CO₂ had no influence on the degradation potential of Pleurotus ostreatus.

Mixing the wood chips with loamy soil did not affect the degradation process of PCBs. However, direct application of xenobiotics to the soil prior to mixing with wood chips greatly reduced the speed of their degradation. After 7 weeks, only 50%‐60% of the degradation obtained on wood chips were observed in this system, in spite of the fact that the overall composition of the solid state system was identical. The present study demonstrates in general that the elimination of these recalcitrant substances is possible in wood and soil samples. The lower rate of PCBs degradation in soil may be due to general lowered bioavailability of contaminants.

Key Words:

• PCB
• white rot fungi biodegradation
• Pleurotus ostreatus
• Trametes versicolor