Bioavailability of trace metals to marine bivalves mediated by dissolved and colloidal organic carbon

The significant roles of colloidal nanoparticles or macromolecules in the biogeochemical cycling of trace metals and thus the interaction between organic matter and trace metals in aquatic environments have been demonstrated recently. In this study laboratory experiments employing radiotracer methodology and ultrafiltration techniques were conducted to examine the influences of natural dissolved organic carbon (DOC) and colloidal organic carbon (COC) on the bioavailability of trace metals (Fe, Cr, Ag, Cd, and Hg in forms of inorganic and methylated) to the green mussel Perna viridis (and the clam Ruditapes philippinarum for Cr and Fe) at different concentrations of DOC and COC from different origins (estuarine, coastal, and diatom decomposed). The differential utilizations of organic carbon by the marine mussels through the assimilation of five phytoplankton diets and from the dissolved phase were also investigated. Standard compounds (glucose, amino acids arginine and leucine, and high molecular weight carbohydrate particles with size ranging from 3 to 2000 kDa) were used to study the organic matter flux into the green mussel P. viridis. The results demonstrated that natural colloid-bound metals were bioavailable to the green mussels and clams. The influences of COC on metal bioavailability were metal-specific and dependent on the geochemical properties of colloids and colloid-metal complexation.; Using the DOC originating from the decomposed diatom (Thalassiosira pseudonana), I demonstrated that Cd and Cr uptake increased linearly with increasing DOC concentration. While this biogenic DOC decreased the uptake of Hg(II). The bioavailability of McHg was weakly influenced by different DOC quality or quantity.; Results demonstrated the direct accumulation of biogenic DOC obtained from the diatom decomposition, and the significant utilization of COC as nutrients of the mussels, A variety of HMW dextrans (at substrate concentrations of 0.2 to 2 mg L-1) were actively ingested by the mussels.{09}A kinetic model was applied to quantitatively evaluate the carbon contribution from the dissolved and particulate sources to the general organic carbon utilization of the mussels. It appears that the mussels were able to utilize colloids of different sizes, thus playing an important role in the cycling of DOC in the coastal waters.