Microbial mineralization of humic acid-3,4-dichloroaniline complexes

Abstract

3,4-Dichloroaniline (DCA), a biodegradation intermediate of numerous herbicides, binds covalently to soil humus to form persistent complexes. Prompted by the possibility that, upon repeated treatments, xenobiotic residues may accumulate in humus, the turnover rates of intact, solvent-extracted, and hydrolyzed humic complexes of 14C-DCA were compared with that of similarly-treated soil organic matter fractions. The turnover rate of intact humic-DCA complexes was considerably faster than the average turnover of soil organic matter. Humic-DCA complexes, that had been washed in solvents to remove adsorbed DCA or hydrolyzed to break susceptible chemical bonds, had turnover rates that were equal to or slower than that of the average soil organic matter, respectively. However, the turnover rates of the solvent-washed and hydrolyzed humic-DCA complexes were similar to that of identically-treated humic acid. The evidence indicates that an extensive accumulation of DCA or similar herbicide-derived halogenated anilines in soil organic matter is unlikely.