PCB removal, soil enzyme activities, and microbial community structures during the phytoremediation by alfalfa in field soils

Purpose An in situ phytoremediation trial was developed in order to investigate the function of alfalfa during a 2-year bioremediation of an agricultural soil contaminated with polychlorinated biphenyls (PCBs). The study was conducted with the aim to better understand the application potential of PCB phytoremediation at field scale. Materials and methods Two treatments were set up in this field study: (1) soil without planting as a control (CK), and (2) soil planted with alfalfa (P). Kinetics of soil PCB removal during the bioremediation treatment was determined using gas chromatography. Soil enzyme activities including dehydrogenase and fluorescein diacetate (FDA) esterase were detected by spectrophotometry. In addition, soil microbial community structures were investigated by using denaturing gradient gel electrophoresis (DGGE). Results and discussion After the first and second years of remediation, planting alfalfa significantly decreased the initial soil PCB concentrations by 31.4% and 78.4%, respectively. Moreover, the presence of alfalfa significantly increased soil dehydrogenase and FDA esterase activities during the remediation. Changes in soil bacterial community structure and diversity were observed by PCR-DGGE fingerprinting. Planting alfalfa significantly increased soil bacterial diversity. Some well-known PCB-degrading bacteria such as Chloroflexi sp. may have contributed to the rhizoremediation of PCBs. Conclusions Results of this field study suggest that alfalfa is a promising candidate for phytoremediation of PCB-contaminated agricultural soil.