Facilitation of humification of recalcitrant chlorinated organic compounds via the catalytic oxidation and toxicity of humification products

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Humic substances (HSs) were extracted from 14-types of soils, and the correlations between the parameters of humification (e.g. elemental composition and contents of acidic functional groups) and the percentages of pentachlorophenol (PCP) degradation were investigated in the catalytic oxidation system with iron(III)-porphyrin complex and KHSO_5. It found that the percentages of PCP degradation were largely reduced by the presence of HSs, which were of lower degree of humification (Environ.Sci.Technol. 2003,37,1031). On the other hand, PCP was oxidized to reaction intermediates, such as phenoxy radicals, and this resulted in the formation of humification products via the radical coupling. A bioassay (Microtox test) of the reaction products demonstrated that the toxicity of PCP was largely reduced by forming the humification products (Environ.Sci.Technol. 2003,37,386). When the catalytic system with iron(III)-porphyrin complex and KHSO_5 was applied to the PCP-contaminated soil, the PCP removal from the soil was enhanced by adding peat HS. This implies that the addition of HS with lower degree of humification is useful for the detoxification of PCP-contaminated soils (Toxicol.Environ.Chem. 2003,85,39). In addition, other biomimetic catalysts as well as iron(III)-porphyrin complex, such as iron(III)-phthalocyanine and manganese(III)-porphyrin complexes, were also useful for enhancing PCP degradation in the presence of peat HSs. I supposed from the model experiments using cyclodextrin that such effects of HS with lower degree of humification may be attributed to the interactions between biomimetic catalysts and the sugar moieties in HSs (J.Mol.Catal. A, in press).