Fate and toxicity of chlorophenols, polychlorinated dibenzo-p-dioxins, and dibenzofurans during composting of contaminated sawmill soil

We studied the fate of chlorophenols during the composting of sawmill soil and impregnated wood to see whether chlorophenols, in addition to mineralization, would form any harmful metabolites. The toxicity assessed by luminescent bacteria tests decreased during the composting, and it followed the chlorophenol concentrations in the compost piles. The threshold value for chlorophenol toxicity appeared to be 200 mg of total chlorophenols/kg dry weight. Polymerization of chlorophenols was studied by determining the molecular weight distribution of organic halogen compounds during the bioremediation. Organic chlorine compounds appeared in high molecular weight sizes, indicating that binding to soil organic matter had taken place during the long exposure time to the wood preservative Ky-5 in the contaminated soil. No major polymerization occurred during the composting, but the polymerized fraction was not either degraded or remobilized. Large amounts of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) originating from the wood preservative were found in the compost piles, but their concentrations did not significantly change during the bioremediation process. The congener composition of PCDD/Fs resembled the one in original wood preservative. Since PCDD/Fs were released from the wood chips of the former Ky-5 dipping basin and not degraded during the bioremediation, it is not recommended to treat PCDD/F-contaminated wood chips in biopiles.