Desorption of chlorinated organic compounds from a contaminated estuarine sediment

Abstract

AbstractBatch 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 (Koc) 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 × 10−4 to 2.5 × 10−2/d and was negatively correlated with the contaminant hydrophobicity (Koc).