Phytodegradation of p,p′-DDT and the enantiomers of o,p′-DDT

The reductive dechlorination of p,p'- and o,p'-DDT at the mu g/mL level in the presence of the aquatic plant Elodea (Elodea canadensis) and the terrestrial plant kudzu (Pueraria thunbergiana) is described; studies included analysis of the enantiomers of chiral o,p'-DDT and its chiral degradation product, o,p'-DDD, to determine whether the reaction was enantioselective. The degradation process was followed by GC using a gamma-cyclodextrin-based chiral phase. The half-lives for degradation of both o,p'- and p,p'-DDT by Elodea and kudzu ranged from 1 to 3 days, apparently depending on growth conditions of the plants. The only products identified were o,p'- and p,p'-DDD; no DDE or DDA were detected. Phytodegradation experiments using Elodea and carbon-14 labeled p,p'-DDT indicated that up to 22% of DDT analogues were covalently bound within the plant. DDT degradation by Elodea was only about 40% slower after gamma irradiation at 300 krads, indicating the major process not to be dependent upon live microbes. Dead Elodea was shown to maintain reductive activity at about the same rate as fresh plants. The reactions with Elodea and kudzu were not enantioselective in the formation of o,p'-DDD from o,p'-DDT. Reductive dehalogenation of o,p'-DDT by a partially purified extract of Elodea, by the porphyrin hematin, and by human hemoglobin was also shown to be nonenantioselective, with reaction rates similar to that for the whole plant. This evidence suggests that the phytodegradation process may be catalyzed by an achiral enzyme cofactor or other achiral biomolecule.