ABSTRACT
Hydrophobic organic chemicals, such as PCBs and PAHs, often have large partition coefficients, on the order of 103 to 106 L/kg or even higher. In this case, much of the chemical is sorbed to particulate matter and is transported with it. This particulate matter, along with the sorbed HOC, usually settles onto the bottom of an aquatic system and forms deposits of contaminated sediments there that can be many meters thick. At most sites with contaminated sediments, approximate calculations of the amounts of contaminants in these bottom sediments and also in the overlying water lead to the conclusion that there are orders of magnitude more contaminant in the bottom sediments than in the overlying water. As a result, even after the cleanup of point sources of contamination, these bottom sediments can serve as a major and long-lasting source of contaminants to the overlying water. To predict sediment and water quality over long periods of time, the flux of these contaminants between the bottom sediments and the overlying water needs to be quantitatively understood and modeled.
