Desorption of chlorinated organic compounds from a contaminated estuarine sediment

Batch kinetic and equilibrium partitioning experiments were performed to determine the desorption rate and extent of chlorobenzenes and hexachlorobutadiene found in a contaminated estuarine sediment. A small fraction (less than 3%) of most sediment contaminants desorbed in a single-step batch test performed over 62 d. When a desorption test was conducted with contaminated sediment and successive replenishment of the supernatant, the desorbed contaminant fraction increased to as high as 17% after 33 successive desorption steps were completed. The 1,2,4-trichlorobenzene isomer attained the highest extent of desorption. The desorbed contaminant fraction strongly correlated to the organic carbon-based partition coefficient (K-oc) of the contaminants. The two-site model was used to describe the desorption of chlorinated organic compounds from the sediment. Partition coefficients were determined both experimentally and by a computer optimization technique based on the batch desorption kinetic data and the two-site model. The first-order rate constant for the desorption of the contaminants from the ''slow'' desorption sites ranged from 1.1 x 10(-4) to 2.5 x 10(-2)/d and was negatively correlated with the contaminant hydrophobicity (K-oc).