Effect of oil on polychlorinated biphenyl phase partitioning during land biotreatment of impacted sediment

This study evaluated the partitioning of polychlorinated biphenyls (PCBs) during long-term, passive, land biotreatment of PCB-impacted industrial lagoon sediments. Over six years under field conditions, two land treatment units (LTUs) experienced 40% total PCB reductions from initial concentrations of 8-10 mg/kg. A third LTU with 113 mg/kg initial total PCBs showed little reduction over five years. In each unit throughout the study, oil concentrations declined at a rate greater than that for PCBs. Measured aqueous equilibrium concentrations for the PCB-impacted sediments were typically an order of magnitude or more smaller than values estimated using correlations based on total organic matter partitioning. Measured aqueous PCB concentrations agreed with predictions based on equilibration with a PCB-containing oil phase, best modeled by Raoult's law. It was postulated that, as a consequence of PCB oil-phase partitioning, biotreatment would lead to higher PCB concentrations in the oily matter and thus increased PCB partitioning to the aqueous phase if the degradation of oily matter proceeded faster compared to PCBs. Such was the case in this study, wherein low-level aqueous phase PCB concentrations of tetrachloro PCBs increased several fold over the years as oily matter was degraded. The contribution of oil to PCB partitioning needs to be incorporated in the assessment of risk and treatability goals for land biotreatment of contaminated sediments from industrial sites.