Effect of Cu 2+ on the Laccase-Inducted Formation of Non-Extractable Residues of Tetrabromobisphenol A in Humic Acids.

We used 14  C-radiolabelling to study the non-extractable residues (NERs) formation of tetrabromobisphenol A (TBBPA) in a humic acid (HA) suspension under catalysis of laccase in the presence of copper. When entering the suspension after TBBPA adsorbing to HA supramolecular associates, Cu 2+ at low concentrations (even without toxicity to laccase) significantly reduced the amount and first-order kinetic constant of the NER formation, while Cu 2+ had no significant effect on the formation after it was complexed with HA. The inhibition effect of Cu 2+ on the NER formation is explained to be attributed to the prevention of laccase-induced oxidation of TBBPA in the voids of HA associates by complexation of Cu 2+ with periphery molecules of the associates. The results provide insights into varying effects of heavy metals on the environmental fate of organic contaminants and suggest that co-existing heavy metals could increase their environmental risk by reducing their NER formation.