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Distribution of Trace Elements in Sediments and Aquatic Biota in Streams of the Santee River Basin and coastal drainages, North and South Carolina
Thomas A. Abrahamsen
U.S. Geological Survey, Stephenson Center, Suite 129, 720 Gracern Road Columbia, South Carolina, 29210-7651, USA


As part of the National Water Quality Assessment (NAWQA) Program of the U.S. Geological Survey, 26 sediment samples and 30 tissue samples were collected from streams of the Santee River Basin and coastal drainages (SANT) in North and South Carolina, during 1995-97. Samples were analyzed for the concentrations of 43 elements in sediments and 21 elements in tissues. Nine of the elements have been designated as priority pollutants by the U.S. Environmental Protection Agency. Within the SANT study area, there was a distinct concentration gradient for seven of the nine elements. The concentrations of chromium, copper, nickel, and zinc in sediments decreased from the Blue Ridge Ecoregion through the Southeastern Plains to the Coastal Plains. In contrast, the concentrations of cadmium, mercury, and selenium in sediments increased along the same gradient. The concentrations of arsenic and lead in sediment were not significantly different among ecoregions. Those elements with the highest concentrations were zinc, chromium, and lead. None of the elements in sediment exceeded the threshold concentration harmful to aquatic life; they pose no threat to the biota in the steams.

Among the priority pollutant trace elements in tissue, there was no significant ecoregion distributional gradient. Copper and zinc were bioconcentrated more readily by carp (Cyprinus carpio) than by Asiatic clams (Corbicula fluminea). The clams concentrated selenium and mercury. Chromium, lead, and nickel were not accumulated, or were rapidly eliminated by clams and carp. Mercury was the sole element for which fish consumption advisories have been issued by state regulators in the SANT study area. Mercury concentration in Asiatic clams in one river was more than an order of magnitude greater than the concentration in the sediments.

Scatter plots of trace element data show that there was no significant correlation between the concentrations of trace elements in sediments and biota. Patterns of concentration in tissue and sediment imply that only a fraction of the priority pollutant trace elements in sediment are being bioaccumulated, and suggest that clams may be assimilating trace elements through routes other than sediment contact.

--- March 1999

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