SORPTION OF POLYCHLOROBIPHENYL (PCB) CONGENERS BY RESIDUAL PCB-OIL PHASES IN SOILS

In this report we show that residual polychlorobiphenyl (PCB) oil present in soils heavily contaminated with PCB mixtures (Aroclors) functions as a highly effective partitioning medium accounting for the sorptive uptake of 2-chlorobiphenyl from water. A PCB-oil normalized partition coefficient (K(PCB)) was evaluated from the experimental sorption data of 2-chlorobiphenyl onto four PCB-oil contaminated soils which had PCB-oil contents ranging from 2.17 g/kg to 7.67 g/kg (2170 ppm-7670 ppm). This K(PCB) value (114 000) indicates that the residual PCB-oil phase in soils, as a partitioning medium for 2-chlorobiphenyl, is approximately 67 times more effective per unit mass than natural soil organic matter (K(OM) = 1700) and 3.5 times more effective than octanol (K(OW) = 32 400). Our results suggest a threshold PCB concentration in soil of about 0.1% (w/w), above which the PCB mixture forms a separate sorptive phase. The threshold concentration may correspond to the solubility of the liquid PCB mixture in natural soil organic matter. Because of its greater sorptive effectiveness, the PCB-oil phase, once formed, will primarily determine the soil-water distribution of individual PCB congeners. Accurate prediction of the soil-water distribution of PCB congeners in such soils can be obtained by considering the additive sorptive effects of the anthropogenic and natural organic matter phases.