Subsurface and plant contamination during natural attenuation and phytoremediation of silt loam contaminated with chlorinated organic compounds

Although natural attenuation and phytoremediation can be cost-effective alternatives for the remediation of soils contaminated with volatile organic compounds (VOC), the risk of groundwater and plant contamination during the remediation process cannot be disregarded. In this study, the potential for subsurface contamination during natural attenuation as well as for plant contamination and recovery during phytoremediation in soils contaminated with 1,1,1-trichloroethane (TCA), trichloroethylene (TCE), and tetrachloroethylene (PCE) were investigated using a total of 56 polyvinyl chloride (PVC) columns filled with soil freshly contaminated by TCA, TCE, and PCE. Contaminant concentrations of soil gas, leachate, plant roots and shoots, and soil microbial biomass were monitored. The impact of easily degradable microbial substrate addition during natural attenuation on subsurface contamination was also examined. The results showed that VOCs migrated into deep soil or groundwater during natural attenuation and phytoremediation, and hence, the manner in which a site is initially managed is important for the effective application of natural attenuation and phytoremediation of VOC-contaminated soil. In addition, the use of plant species that are fast growing under local environmental conditions was an effective technique for reducing the release of VOC into deep soil. The addition of substrate during natural attenuation helped to reduce subsurface contamination for all three VOC-contaminated soil systems, particularly PCE. The VOC were first detected in root and then in shoot samples as the experiment progressed. The VOC in plant shoots, unlike those in roots, still remained after the soil was cleaned. Thus, careful plant management should be considered during VOC phytoremediation.