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Transformation of Chlorinated Phenols and Anilines in the Presence of Humic Acid

Lab. of Soil Biochemistry, Center for Bioremediation and Detoxification, The Pennsylvania State Univ., University Park, PA 16802;
Dep. of Agricultural Chemistry, Kyungpook National Univ., Taegu 702-701, Korea.

^* Corresponding author (jmbollag{at}psu.edu).

ABSTRACT

Incubations of chlorinated phenols and anilines with oxidoreductive catalysts (peroxidase, laccase, tyrosinase, and birnessite) in the presence of humic acid led to oligomerization of the substrates or their binding to organic matter. The effect of humic acid on the overall transformation depended on the substrate, type of catalyst, and the concentration and source of humic acid. At low humic acid concentrations (<10 mg/L), the transformation of 4-chlorophenol (4-CP) was enhanced, but at higher concentrations of humic acid (>10 mM), no further enhancement occurred. The transformation of 4-chloroaniline (4-CA) was only slightly affected after the addition of humic acid. In experiments with ¹⁴C-labeled substrates, 4-CP was mainly bound to humic acid and formed few oligomers, whereas 4-CA was largely subject to oligomerization with less binding to humic acid. Binding and oligomerization of 4-CP did not change with increasing concentration of humic acid, but with 4-CA, binding increased and oligomerization decreased. It appears that nucleophilic binding of 4-CA depended largely on the availability of carbonyl and quinone groups in humic acid and, therefore, the distribution of the transformed substrate between oligomers and organic matter greatly depended on the source of humic acid.