PCDD/F formation from chlorophenols by lignin and manganese peroxidases

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) formation was studied, in vitro, with two different chlorophenol mixtures (group di+tri 2,4-dichlorophenol; 2,3,4-, 2,3,5-, and 3,4,5-trichlorophenols and group tri+tetra+penta with 2,4,5-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) and two different lignolytic enzymes, lignin and manganese peroxidase (LiP and MnP respectively), which can be found during the composting process of sewage sludge. The concentrations of PCDD/F in final samples are compared to the PCDD/F content of the control samples containing the chlorophenols. High increases were observed for experiments with MnP and phosphate buffer. Experiments that contained tri-, tetra- and pentachlorophenol with MnP resulted in more than 8 . 10(8) ng of OCDD kg(-1) chlorophenol which was much higher than the initial amount (1 . 10(7) ng OCDD kg(-1) chlorophenol). In relation to LIP experiments, only those at 37 degrees C showed a moderate increase (from 1.3 . 10(7) to 2.6 . 10(7) ng of OCDD kg(-1) chlorophenol). The results agree with the literature in which high amounts of HpCDD and OCDD were found after a composting process and could explain the biogenic formation suggested by others, but the incidence on the total toxicity is less than that expected. (C) 2014 Elsevier Ltd. All rights reserved.