Potential for phytoremediation of polychlorinated biphenyl-(PCB-)contaminated soil

Weathered soils contaminated with commercial-grade Aroclor 1260 from three sites in Canada were used to investigate the polychlorinated biphenyl (PCB) phytoextraction potential of nine plant species (Festuca arundinacea, Glycine max, Medicago sativa, Phalaris arundinacea, Lolium multiflorum, Carex normalis, and three varieties of Cucurbita pepo ssp. pepo) under controlled greenhouse conditions. The soils used varied in PCB concentration (90-4200 mu g/g) and total organic content (0.06-2.02%). Greenhouse experiments controlled for PCB volatilization through the use of a vented enclosure and by isolating the contaminated soils with parafilm. After 8 wks, PCB concentrations of 47-6700 mu g/g were observed in root tissues. Although PCB concentrations in shoot tissues were lower (< 1-470 mu g/g), the absolute amounts of PCBs observed in shoot tissue were significant (1.7-290 mu g) once shoot biomass was accounted for. Congener signatures indicated that tetra- to hexa-chlorobiphenyls contributed the largest proportions to shoot tissues, but heptato nona-chorobiphenyls were also present in measurable amounts. Overall, the results indicate that varieties of C. pepo were more effective at extracting PCBs from soil than other plants screened. The evidence suggests that this was mainly due to root uptake of PCBs and tranlocation to the shoots, rather than volatilization of PCBs from soil. All plants screened showed signs of stress in the most highly contaminated soil (4200 mu g/g), but not in the two lower PCB contaminated soils (250 and 99 mu g/g, respectively). No detectable decreases in soil PCB concentrations were observed in these short-term greenhouse experiments, but the results suggest that this may be achievable through multiple plantings.