Distribution and Accumulation of Trichloroethylene and Trichloroacetic Acid in Hybrid Poplars

Abstract

Hybrid poplar trees are known to take up trichloroethylene (TCE) into above ground tissues, where it degrades into the metabolites trichloroacetic acid (TCAA), dichloroacetic acid, and trichloroethanol and where parent chlorinated solvents volatilize to the atmosphere. Based on this knowledge, numerous phytoremediation applications have been implemented for TCE and other chlorinated solvents. Sampling of plant tissues has proven effective for phytoforensic and phytoscreening applications in assessing sites and evaluating the efficacy of phytoremediation. However, little is known about the appropriate exposure times and sampling locations required to obtain an accurate assessment of TCE and metabolites. In this study, hybrid poplars were dosed under greenhouse conditions for times ranging from one hour to 29 weeks. No increasing accumulation of TCE occurred in the stems over the time periods; however, concentrations decreased with increasing stem height in all cases. The concentration of TCAA throughout the plants’ leaves fluctuated along the stem rather than following a decreasing pattern with height. However, as a result of its nonvolatile characteristics, TCAA did accumulate to higher concentrations in the leaves over the given time periods. These results revealed that sampling TCE in the lower stem/trunk was ideal, but TCAA concentrations varied across locations; thus, sampling of multiple leaves is appropriate for an accurate determination of accumulative contaminant uptake. Used together, these methods offer a novel monitoring tool, which is needed because phytoremediation does not offer traditional monitoring means such as treated effluent to assess fate and efficacy. Knowledge resulting from this research can improve monitoring and reduce long-term monitoring costs for chlorinated solvent sites.