BINDING OF 3,4-DICHLOROANILINE BY HUMIC ACID AND SOIL

Abstract

Anaerobic reaction conditions and prereduction by sodium borohydride decreased the ability of humic acid to covalently bind the herbicide residue 3,4-dichloroaniline. The above conditions and treatments also reduced the resistance of the remaining bonds formed to subsequent alkaline hydrolysis. 3,4-Dichloroaniline was partially displaced by exchange with other amines from its intact, but not from its prehydrolyzed, humic acid complexes. The above results are consistent with the theory that quinoidal groups on the humic acid molecule are the primary sites of attachment for 3,4-dichloroaniline, and that subsequent addition and oxidation reactions eventually lock the amino nitrogen into heterocyclic ring systems. At this advanced stage of binding, release of DCA by exchange or hydrolysis becomes extremely difficult. A 5-month study in soil demonstrated the progressive binding of DCA and the increasing resistance of the bound DCA to exchange with anhydrous ammonia. It also indicated that fertilization of agricultural soil by anhydrous ammonia is capable of mobilizing humus-bound xenobiotic amines, thus increasing their crop-contamination potential.