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Streambed sediment provides habitat for many benthic organisms in aquatic environments and also acts as a source or sink for persistent and toxic chemical constituents, including many trace elements and organic compounds. The quality of aquatic sediment is of particular interest because of the potential for accumulation of toxic constituents in aquatic organisms, also. Sources of trace elements and organic compounds in streambed sediment include atmospheric deposition, industrial inputs, wastewater discharges, landfills, and storm-water runoff. The U.S. Environmental Protection Agency has identified, as areas of probable concern, five watersheds in the lower Tennessee River Basin (Guntersville, Upper Kentucky, Lower Kentucky, Wheeler, and Wilson) where potential adverse effects of sediment contamination may be found.
As part of the U.S. Geological Survey's National Water-Quality Assessment Program to evaluate water quality in the lower Tennessee River Basin, data were collected to determine the occurrence and distribution of trace elements and organic compounds in streambed sediment. Streambed sediment samples were collected in August and September 1998 at 12 sites in the lower Tennessee River Basin and analyzed for 47 trace elements and 107 organic compounds. Sites were located in basins with agricultural, urban, and mixed land uses. Out of 47 trace elements, 41 were detected in streambed sediment at all sites. Out of.107 organic compounds analyzed, 34 were detected in streambed sediment.
Currently, no State or U.S. Federal guidelines or standards exist for concentrations of trace elements and organic compounds in sediment. The Canadian government has established interim sediment-quality guidelines (ISQG's) for the protection of aquatic life. These guidelines were established for trace elements and organic compounds considered most toxic to aquatic life. The ISQG's for arsenic [5.9 micrograms per gram (µg/g)] and chromium (37.3 µg/g) were exceeded at all 12 sites. Concentrations of zinc in streambed sediment were above the ISQG (123 µg/g) at two sites in Alabama--lndian Creek near Huntsville, Alabama (150 µg/g), and Scarham Creek near Guntersville, Alabama (140 µg/g). Concentrations of benzo[a]pyrene, benz[a]anthracene, dibenz[a,h]anthracene, flouranthene, phenanthrene, and pyrene in streambed sediment at Indian Creek also were above ISQG's. Concentrations of the pesticides DDT (the sum of p,p' DDT and o,p' DDT isomers) (10.2 µg/g) and p,p' DDE (13µg/g) were highest at Indian Creek. Concentrations of DDT at Indian Creek were also above the ISQG (1.19 µg/g).
U.S. Department of the Interior, U.S. Geological Survey
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