Soil-water partitioning and desorption hysteresis of volatile organic compounds from a Louisiana Superfund site soil

The adsorption and desorption of three volatile organic compounds (1,2- dic hloroethane, 1,1,2- trichloroethane and 1,1,2,2-tetrachloroethane) from a p reviously uncontaminated clayey soil sample from a Superfund site in North Baton Rouge, Louisiana was studied. In the linear range of the adsorption i sotherm, the partition constants were not affected by the presence of the c o-solutes. The adsorption isotherms over a wide concentration range on the soil followed the nonlinear Freundlich isotherm. The desorption of the comp ounds showed significant hysteresis at all concentrations studied. Approxim ately 20 to 70% of the adsorbed mass of organic compounds resisted the deso rption even after five months of successive desorption steps. The desorptio n of four compounds (1,2-dichloroethane, 1,1,2-trichloroethane, 1,4-dichlor obenzene and hexachlorobutadiene) from a contaminated soil sample from the same site was also studied. The aqueous concentration declined as the succe ssive desorption steps progressed. For hexachlorobutediene the desorption c an be visualized as occurring in two stages. The first stage involved a `lo osely bound' or `reversible' fraction and the second stage involved a `tigh tly bound' or `resistant' fraction.