Mobility and Adsorption of Trace Elements in a Coal Residues-Affected Swamp

A study was conducted to determine the mode of transport of Cd, Cu and Ni through the Steel Creek sediments at the Savannah River Site and to find the adsorption of these metals to the sediments. The sediments collected from three adjacent sites showed considerable heterogeneity but had a uniform pH approximating 6.0. Three periodic collections of sediment cores (0–20 cm) from two sites and surface sediments (0–10 cm) of 3rd site were analyzed for three metals in the pore water and DTPA extract of wet sediments. The concentrations of dissolved metals in the pore water were quite low in the ranges of 0.02–0.5 µg L−1 Cd, 0.0–6.0 µg L−1 Cu, and 2.3–11.9 µg L−1 Ni. DTPA-extractable metals in the sediments ranged 0.0–34.67, 0.0–491.4, and 44.6–676.4 µg L−1 for Cd, Cu and Ni, respectively. Surface water enclosed in two polyethylene chambers imbedded in the stream path was spiked with 100 µg L−1 of each metal. The metals moved downward and outside the chambers through the sediments and equilibrated with the ambient within two weeks. Adsorption study with seven sediment samples using Cd and Cu solutions in the concentration range of 50–110 µg L−1 provided essentially linear adsorption isotherms at 25°C with significant correlation coefficients. The amounts of Cd adsorption were greater as compared to Cu adsorption. Study revealed low concentrations of dissolved metals in the surface and pore water and but relatively high adsorption by the sediments and particulate matter which forms the mobility pattern of these metals as a mechanism of transport in the swamp system.