Enhancing dissipation of aroclor 1248 (PCB) using substrate amendment in rhizosphere soil

Soils contaminated in the laboratory with Aroclor 1248 (PCB) were amended with biphenyl and plant residues that are known to induce PCB degradation, and planted with crops that inherently stimulated PCB dissipation in a previous study to determine if the combination of soil amendment and planting could further enhance PCB dissipation beyond that shown by planting alone. The plants used were flat pea (Lathyrus sylvestris), reed canarygrass (Phalaris arundinacea), and burr medic (Medicago polymorpha). They were grown in laboratory microcosms at a 12h photoperiod in soil containing 50mg/kg PCB. Portions of soil were amended with biphenyl (1,000 mg/kg), ground pine needles, or orange peels (2% w/w), and a portion was left unamended to serve as control. After nearly 100d, PCB recoveries ranged from 69% of initial applications in unplanted soil to 65, 59 and 55% of initial levels in soils that were unamended but planted with flat pea, reed canarygrass and burr medic respectively. PCB recoveries in soils that were amended, but left unplanted ranged from 59% of initial applications in pine needle amended-soil to 48 and 45% in biphenyl- and orange peel-amended soils respectively. Combinations of soil amendment and planting enhanced PCB dissipation in soil compared to planting alone, except the combination of biphenyl amendment and planting with burr medic, where the soil still contained nearly 80% of the initial PCB additions after about 100 d. Estimates of bacterial populations were generally slightly to significantly higher in orange peel and biphenyl-amended soil than in unamended soil, except in biphenyl-amended soil that was planted with burr medic, where bacterial counts were significantly lower than in most of the other treatment combinations.