Phytoforensics tools: The degradation and detection of chlorinated solvents in integrated systems

Due to decades of mismanaged pollutants entering groundwater, subsurface pollution of various compounds has become a widespread challenge. Chlorinated solvents are the most common groundwater contaminants that persist in aquifers, and remediation of these wide-spread plumes is difficult. Bioremediation, permeable reactive barriers, and phytoremediation are remedial technologies that have been developed and applied to chlorinated solvents in groundwater systems. This study integrates these technologies in different combinations to demonstrate the remediation potential of this approach. Zerovalent iron (ZVI) and bioaugmentation with a Dehalococcoides sp. (DHC) culture were applied separately and in combination for degradation of perchloroethene (PCE). Salix pentandra were planted in reactors and concurrently served as monitoring tools. Characteristics studied between reactor combinations included plant health, contaminant degradation rates, and water uptake. By creating an area of lower water potential, trees direct groundwater flow through the reactive zone and uptake the contaminated groundwater after contaminant degradation. Classroom experiential learning of this study was implemented to introduce phytoforensics to students. ZVI and DHC showed degradation of up to 92.0% and 99.3% reduction of PCE, respectively. Combined, ZVI and DHC increased PCE concentration reduction to 99.7%. Dichloroethene (DCE) was only found in all reactors containing DHC, but in no reactors without DHC. Plant sampling was shown to reveal degradation profiles and offer a low impact, low cost approach to monitoring PCE degradation processes in the subsurface. The degradation of PCE by DHC and ZVI was shown to occur through phytoforensics, and the specific mechanism was elucidated.