The bioavailability of heavy metals in sediments.

摘要

Contaminated metals in sediments can be solubilized during in vitro digestion by incubation with digestive fluids of marine deposit feeders. My objectives are to probe mechanisms of the solubilization process, and examine its impact on deposit feeders and metal biogeochemistry. Good correlations were observed between dissolved amino acids (AA) and metals in gut fluids of a population of healthy Arenicola marina, and 7 other species with contrasting feeding modes in their natural habitats. Coexistence of metals and AA in high-molecular-weight fractions and dramatic enrichment of soft, borderline metals in gut fluids imply the complexation of AA with metals. Normalization metal concentrations to AA concentrations showed a positive relationship between those of gut fluids and tissues of Arenicola marina, suggesting AA as an important link shuttling metals between the two pools. The solubilization of Cu, and perhaps other metals, is a non-enzymatic, simple complexation reaction as indicated by microwave treatment of gut fluid and replacement of gut fluid with solutions of bovine serum albumin. Chemical modification of histidine residues in gut fluids dramatically blocked Cu solubilization, which indicated the importance of histidine, although the involvement of non-histidine residues is also evident. After filling the strong-binding sites (e.g., histidine residues) in gut fluid of Arenicola marina, sufficient amounts of dissolved Cu can interact with the weak-binding, catalytic sites and inhibit digestive proteases. This result suggests that dissolution of sedimentary metals may have ecotoxicological effects on the population dynamics and biodiversity of deposit feeders. Most of the time-courses of metal dissolution during an in vitro digestion showed two-stage reactions: a fast reaction completed within {dollar}le{dollar}2min, followed by a slow, and often reduced, reaction lasting for a few hours. Thus deposit feeders with various gut retention times may be exposed to different pools of sedimentary metals during in vivo digestion. The kinetic patterns varied according to the combination of sedimentary metal-animal species, which is a function of the ratio of gut ligand to metal loading. A conceptual model indicates that bioavailability of sedimentary metals is not a property of either sediments or species of organisms alone, but rather a product of organism-sediment interactions.