Supercritical fluid extraction (SFE) with pure CO{sub}2 was used to quantitatively remove PCBs from historically contaminated sediments without substantially disturbing their bulk organic or inorganic matrix as evidenced by only small orundetectable changes in thermal gravimetric behavior, elemental (C, H, N, S) composition, ionic conductivity, and pH determined before and after SFE. The extracted PCBs were then spiked into water with the parent sediment, and sorption was allowed tooccur for up to 18 days. The selective SFE conditions developed in part 1 were used to determine the proportion of PCBs which could be extracted under four conditions of increasing stringency. Comparing the selective SFE behavior of the PCBs from thewater/sediment sorption samples to the original historically contaminated sediments demonstrated that 18 days was not sufficient for PCBs to migrate to the "slower" sediment-binding sites (those sites requiring more rigorous SFE conditions), which thePCBs had occupied in the historically contaminated sediments and that the adsorbed PCBs were primarily associated with the binding sites most easily extracted ("rapidly desorbed") by SFE. Sediment/ water distribution coefficients at 18 days were similarfor sediments with low contamination levels (<50 ng/g of individual congeners) and high contamination levels (~3004000 ng/g). Apparent distribution coefficients (K{sub}(dS)) at 18 days were similar (within a factor of 2) for the various sedimentsregardless of congener molecular weight or concentration. K{sub}(dS) increased by a factor of～4-8 when exposure was increased from 2 h to 18 days, with the most rapidly sorbed molecules corresponding to those molecules most rapidly desorbed by selectiveSFE.
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