Abstract
The transformation of carbon tetrachloride (CT) and hexachloroethane (HCA) by aquatic plants and freshwater algae was investigated. Stressed, axenic, and physiologically healthy freshwater plants all transformed the two chlorinated alkanes, yielding similar breakdown products. Experiments conducted with dead plants were used to indirectly test the hypothesis that dead aquatic plants maintain and possibly contribute to the dehalogenase activity observed in organic-rich sediments. After exposure of the aquatic plants and algae to HCA- and CT-dosed solutions, a rapid sorption (or sequestration) step followed by a slow transformation lasting several hours thereafter was observed. The kinetics data were adequately described by two first-order rate equations; pseudo-first-order sorption rate coefficients were calculated for the initial rapid adsorption and transformation steps. The identified metabolites extracted from plants indicated that more than one pathway, possibly requiring different reactants, mediated the phytotransformation reactions. Mass balance estimations confirmed that >80% of the parent chemical was sequestered, transformed, and/or assimilated by the biomass. The metabolic activity observed with dead plants and algae suggests that photoautotrophs maintain this activity at death, and the active agents could become bound to the sediment-organic matrix as plants die, decay, and are buried in sediment. The results of this study suggest the potential usefulness of aquatic plants and freshwater algae in the removal of chlorinated alkanes from water and remediation of aquatic environments.