RESUMO
Effects and mechanisms of heavy metals Cu, Cd and Pb on the growth of white-rot fungus P. chrysosporium and its ability of BDE-209 degradation were studied. The results showed that low concentrations of heavy metals (< or = 1 mg x L(-1)) stimulated the growth of P. chrysosporium with the order of Cd > Pb > Cu when 1 mg x L(-1) of each heavy metal was concerned, while high concentrations (> 1 mg x L(-1)) depressed it. P. chrysosporium degraded BDE-209 efficiently with degradation efficiency reaching 69.7% after 7 days. The presence of heavy metals significantly influenced the capability of P. chrysosporium to decompose BDE-209 (P < 0.05). Low concentrations of Cu (< or = 1 mg x L(-1)) and Cd (< or = 0.5 mg x L(-1)) accelerated the degradation of BDE-209 and the degradation efficiency was enhanced from 69.7% to 84.4% when 1 mg x L(-1) Cu was present, while Pb had negative effect. On the other hand, all three metals under high concentrations (> 1 mg x L(-1)) showed depressed effects on the degradation in the order of Cd > Pb > Cu. The growth of P. chrysosporium did not completely positively correlate with the degradation capability of BDE-209. The degradation of BDE-209 by P. chrysosporium conformed to the first-order kinetic model. The reaction rate constant k raised firstly and then declined with increasing concentrations of Cu and Cd, and the highest k of 0.321 2 achieved in the presence of 1 mg x L(-1) Cu. By contrast, the constant k declined all the way when Pb existed. A further investigation into the effects of heavy metals on degradation of BDE-209 by extracellular enzymes derived from P. chrysosporium was conducted, and the distance correlation analysis of the degradation by extracellular enzymes and the whole cell was carried out. The results demonstrated that the degradation by extracellular enzymes and the whole cell was 63.7%, 69.7% separately, showing no significant difference of degradation capability between them, which proved that the extracellular enzymes played dominating role in the degradation of BDE-209. Furthermore, the distance correlation coefficient R were all greater than 0.9 when three heavy metals existed, certificating that heavy metals affected the degradation of BDE-209 through the interaction between extracellular enzymes and heavy metals.