Free and bound benzotriazoles in marine and freshwater sediments

To investigate how some anthropogenic compounds are sequestered in sediments, we examined the free and bound fractions of six different substituted benzotriazoles (BZTs) in sediment cores from the Pawtuxet River and Narragansett Bay. The free fraction was operationally defined as the fraction of BZTs that was removed with several organic solvent extractions, and the bound fraction was that portion of BZTs removed by solvent extraction after saponifying the sediment residue remaining from the initial solvent extractions. The total concentrations (free and bound) of BZTs were as large as 10 mg g(-1) in the riverine core and 0.05 mg g(-1) in the estuarine core. The percent bound of the BZTs ranged from 0 to 9% of the total and varied with each compound, sediment depth, and location. BZTs that had alkyl substitution at the 3' position were less likely to be found in the bound fraction than compounds that did not have this substitution. On the basis of these results, it appears that these compounds may be chemically associated with the sediments, and this association is hindered by alkyl substituents on some of the BZTs. These results have important implications in understanding the bioavailability and geochemical fate of organic contaminants in sediments as well as the basic reactions of sedimentary organic matter.