Adsorption-desorption behaviors of hydrophobic organic compounds in sediments of Lake Charles, Louisiana, USA

Neutral organic contaminants commonly reside,on the solid portion of soils and sediments. The extent of desorption from these solids determines the fate, reactivity, and toxicity. Numerous researchers have observed that, after an initial exposure of a few days, desorption takes place in two phases, namely, an initial rapid release followed by a long-term resistant phase. Resistant desorption has been highly unpredictable. In this research, the adsorption and desorption of chlorobenzenes, hexachlorobutadiene, and naphthalene have been studied using historically and freshly contaminated bayou sediments from Lake Charles, Louisiana, USA. After an initial release period, both laboratory-spiked and historically contaminated sediments exhibit similar desorption profiles. The simulations compare favorably with previous in situ measurements. All desorption results, both laboratory and field, could reasonably be interpreted using a single irreversible isotherm. Consequences of these results in terms of sediment quality criteria (SQC) are also discussed. Finally, an index of fractional irreversible adsorption is proposed and tested.