Mechanisms of Cu solubilization during deposit feeding

Large amounts of Cu in contaminated sediments can be dissolved by digestive fluids of deposit feeders during an in vitro digestion (Mayor et al. Environ. Sci. Technol. 1996, 30, 2641) and may subsequently become available to those organisms. The mechanisms of this digestive dissolution were investigated by comparing Cu release potentials of modified and unmodified gut fluids. Microwave treatments indicated that complexation rather than enzymatic action likely accounts for enhanced Cu solubilization by gut fluids rich in protein. Solutions of a common protein, bovine serum albumin, with similar AA concentrations mimicked digestive fluids in releasing sedimentary Cu. Chemical modification of histidine residues in gut fluids drastically reduced Cu release, suggesting their important role in Cu bioavailability. Using an ion-selective electrode, we found an abundance of gut ligand sites with conditional stability constants >10(10), consistent with histidine complexation. Histidine concentrations among various molecular weight fractions of gut fluids can be predictive of the amount of Cu released during in vitro digestion. Complexation-enhanced metal remobilization by gut fluids thus has significant impact on metal availability during deposit feeding.