BINDING MECHANISM AND PERSISTENCE OF HUMUS-BOUND, 3,4-DICHLOROANILINE.

摘要

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, DCA may accumulate in humus, the persistence of the bound residues was investigated. The turnover rates of intact humic-DCA complexes was faster than the average turnover of soil organic matter. The solvent washed and alkali hydrolyzed humic-DCA complexes were mineralized at rates equal to or less than intact soil organic matter, but when compared to similarly treated humic acid (HA), the rates of mineralization were similar. Hence extensive accumulation of DCA in soil is unlikely.; Anaerobic incubation conditions and pre-reduction by sodium borohydride decreased the ability of HA to covalently bind DCA and reduced the resistance of the bound DCA to alakaline hydrolysis. DCA was partially displaced by exchange with other amines from intact but not from pre-hydrolyzed HA-DCA complexes. The above results are consistent with the theory that quinoidal groups on HA are primary binding sites for DCA. Subsequent oxidative reactions bind the amino nitrogen into heterocyclic ring systems. A five-month study in soil demonstrated the progressive binding of DCA and the increasing resistance of the bound DCA to exchange with anhydrous ammonia. Thus mobilization of humus-bound xenobiotic amines by ammonical fertilizers can increase their crop contamination potential.; The role of quinones in the binding of DCA to humus was also investigated by a model complex synthesis approach. DCA was reacted with toluquinone, a monomeric constituent of HA. The product was purified by column chromatography and from spectral analysis the structure was identified as 2-(3,4-dichloroanilino)-5-methyl-benzo-1,4-quinone. HA-DCA complex and the model compound were compared with respect to the bound DCA released by hydrolysis, exchangeability by other amines and biodegradation rates in soil. Based on the similar behavior of HA-DCA complex and the model compound, quinoidal moieties of humic polymers appear to be the primary binding sites of covalent DCA attachment.