The Geochemical Partitionin g and Bioavailability o f Trace Metals in Marine - Sediments

Trace metals in the aquatic environment are generally concentrated o n solid geochemical phases which eventually become incorporated into estuarin e and marine sediments . The mechanism of trace metal concentration is believe d to be adsorption with various geochemical phases such as hydrous metal oxides , clays, and organic matter . Metals in estuarine or marine sediments can thu s 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 organism s will depend on trace metal partitioning and the kinetics of biological meta l uptake from each geochemical phase . The present study was undertaken t o develop models for trace metal partitioning and bioavailability in marin e sediments . An equilibrium adsorption model was developed that can be used to predic t the partitioning of trace metals between different geochemical phases i n aquatic sediments from laboratory studies . The model uses conditiona l equilibrium constants determined from the linear portion of an adsorptio n isotherm . Conditional equilibrium constants determined for the adsorptio n of Cu and Cd on bentonite clay, Fe(OH) 3 , MnO2 , and humic acid in seawater show that the model is applicable for trace metal concentrations existin g 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 marin e sediments . A kinetic bioavailability model was then developed which can be use d to estimate the relative bioavailability of trace metals from both differen t sediment phases and seawater under short term laboratory conditions . This model was used to determine the bioavailability of Cu and Cd from severa l sediment phases (bentonite clay, humic acid, Fe(OH) 3) and seawater to the deposit-feeding polychaete worm, Aharenicola pacifica . The results sugges t 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 .