Pyrolusite (beta-MnO2)-mediated, near dry-phase oxidation of 2,4,6-trichlorophenol

The pyrolusite (beta-MnO2)-mediated oxidation of 2,4,6-trichlorophenol (TCP) under nonaqueous conditions was investigated to assess the potential for abiotic transformations of chlorophenols and their transformation pathways when they are released to soils and the vadose zone. Lower rates of TCP oxidation were found at lower relative humidities, but the rates were still relatively high under near-dry conditions, with 86% of the TCP transformed within 24 h at less than 2% relative humidity. The rates of TCP transformation and soluble manganese formation at less than 2% relative humidity were not affected by atmospheric oxygen content. The manganese oxide-mediated oxidation of TCP resulted in the formation of 2,6-dichloro-1,4-benzoquinone and dimers, including polychlorinated phenoxyphenols and at least one tetrachlorodibenzo-p-dioxin. The products are consistent with the proposed mechanism in which some of the TCP is transformed into trichlorophenoxy radicals that attack TCP and its transformation products. The present results demonstrate that naturally occurring manganese oxides have the potential to oxidize industrial compounds such as TCP; however, the transformation products may be more toxic and persistent than the parent compound.