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Sorption of Polychlorobiphenyl (PCB) Congeners by Residual PCB-Oil Phases in Soils

Department of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824.

^* Corresponding author.

ABSTRACT

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 surptive 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.