Influence of cadmium and mercury on activities of ligninolytic enzymes anddegradation of polycyclic aromatic hydrocarbons by Pleurotus ostreatus in soil

The white-rot fungus Pleurotus ostreatus was able to degrade the polycyclic aromatic hydrocarbons (PAHs) benzo[a]anthracene, chrysene, benzo [k] fluor anthene, benzo [k] fluoranthene, benzo [a] pyrene, dibenzo [a,h] anthracene , and benzo[ghi]perylene in nonsterile soil both in the presence and in the absence of cadmium and mercury. During 15 weeks of incubation, recovery of individual compounds was 16 to 69% in soil without additional metal. While soil microflora contributed mostly to degradation of pyrene (82%) and benz o[a]anthracene (41%), the fungus enhanced the disappearance of less-soluble polycyclic aromatic compounds containing five or six aromatic rings. Altho ugh the heavy metals in the soil affected the activity of ligninolytic enzy mes produced by the fungus (laccase and Mn-dependent peroxidase), no decrea se in PAH degradation was found in soil containing Cd or Hg at 10 to 100 pp m. In the presence of cadmium at 500 ppm in soil, degradation of PAHs by so il microflora was not affected whereas the contribution of fungus was negli gible, probably due to the absence of Mn-dependent peroxidase activity. In the presence of Hg at 50 to 100 ppm or Cd at 100 to 500 ppm, the extent of soil colonization by the fungus was limited.