Polychlorinated biphenyl sorption by soils: Measurement of soil-water partition coefficients at equilibrium

The sorption of PCB congeners 24′ (lUPAC number 8), 22′55′ (52) and 22′44′55′ (153) by eight soils differing in their organic carbon content (2.3 to 0.2% by Wt.) and expandable clay mineral content (17 to 53 % by wt.) has been investigated for 0.1 g/L soil-water suspensions. The time to reach sorption equilibrium, i.e. sorption-diffusion equilibrium, for a highly aggregated montmorillonitic soil containing 0.9% organic carbon for congeners 8, 52, 153 was determined to be 3, 5, and 10 months, respectively, using a gas-purge technique. For these sorbate-sorbent contact times soil-water sorption equilibrium partition coefficients on a soil-organic carbon basis (Koc) were measured and for these congeners ranged varied from 2.4 × 104 to 6.8 × 106 mL/g. Based on these data a correlation relation was derived, log Koc = 1.07 log Kow − 0.98, for estimating Koc from known values of octanol-water partition coefficient (Kow). From literature Kow values this regression equation was used to estimate Koc for 46 of the major PCB congeners in Aroclor 1242, 1254 and 1260.