The geochemical partitioning and bioavailability of trace metals in marine sediments Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8p58ph53v

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  • Trace metals in the aquatic environment are generally concentrated on the surface of solid geochemical phases which eventually become incorporated into estuarine and marine sediments. The mechanism of trace metal concentration is believed to be adsorption with various geochemical phases such as hydrous metal oxides, clays, and organic matter. Metals in estuarine or marine sediments can thus be expected to be partitioned between different phases, depending on the concentration of the phase and the strength of the adsorption bond. The bioavailability of sediment-bound metals to deposit-feeding organisms will depend on trace metal partitioning and the kinetics of biological metal uptake from each geochemical phase. The present study was undertaken to develop models for trace metal partitioning and bioavailability in marine sediments. An equilibrium adsorption model was developed that can be used to predict the partitioning of trace metals between different geochemical phases in aquatic sediments from laboratory studies. The model uses conditional equilibrium constants determined from the linear portion of an adsorption isotherm. Conditional equilibrium constants deterit mined for the adsorption of Cu and Cd on bentonite clay, Fe(OH)₃, Mn0₂, and humic acid in seawater show that the model is applicable for trace metal concentrations existing in the natural environment. Based on the laboratory results, the model predicts that the clay fraction may be a major sink for Cu and Cd in marine sediments. A kinetic bioavailability model was then developed which can be used to estimate the relative bioavailability of trace metals from both different sediment phases and seawater under short-term laboratory conditions. This model was used to determine the bioavailability of Cu and Cd from several sediment phases (bentonite clay, humic acid, Fe(OH)₃) and seawater to the deposit-feeding polychaete worm, Abarenicola pacifica. The results suggest that, under natural conditions similar to those used in this study, the bioavailability of sediment-bound Cu and Cd to A. pacifica can be much more significant than that of seawater.
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