Characterization of the Distribution, Abundance, and Fate of Metals in Sediment

This research describes the mobility of heavy metals in river sediment through characterization of metal-sediment association by a sequential extraction procedure. The most abundant isotopes of As, Cd, Cu, Cr, Pb and Zn were measured by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in four sediment extraction phases: a) exchangeable, b) carbonate-bound, c) metal-oxide-bound, and d) organic-bound. The measured concentrations were compared to the Wisconsin Department of Natural Resources\u27 Sediment Quality Guidelines to determine whether the metals were present at toxic levels. Two reference techniques, Potentiometric Stripping Analysis and Graphite Furnace Atomic Absorption Spectroscopy, were used to validate the concentrations of metals measured by ICP-MS. The six analytes were found to fall below the DNR\u27s levels of concern , thereby suggesting that either the metals are not present or that they are tightly bound to the sediment interface and thus, that the potential for their release into the environment at toxic levels is unlikely under typical environmental conditions. In addition, a column-leaching experiment to simulate the influence of ionic strength on the mobility of Pb in Green Bay sediment was also performed. A different sediment was used because the concentration of exchangeable Pb in any of the Pike River sediment samples was too low. Unexpectedly, lower ionic strength solutions released a greater amount of Pb from sediment. The most plausible explanation for the trend observed is that all of the readily exchangeable Pb was loosely bound by the sediment. However, other factors that influence sediment-metal sorption, such as organic matter mobilization, colloid transport, and the sediment surface characteristics should also be further explored to obtain a greater understanding of the molecular mechanisms of metal release as a result of changing ionic strengths in natural systems