Biological and chemical influences on trace metal toxicity and bioaccumulation in the marine and estuarine environment

For several trace metals, bioavailability and toxicity are controlled by both chemical (free ion) and physiological effects. The role of salinity in trace metal uptake (particularly cadmium) could be explained by a mixture of free ion and biological effects. Mercury (Hg) and methylmercury (MMHg) bioaccumulation is different from that of other metals because uptake of the free metal ion via facilitated transport is not an important mechanism. For microorganisms, it appears that passive uptake of neutral complexes is the controlling accumulation mechanism. However, the observed accumulation in the presence of large organic compounds suggests that other mechanisms of uptake besides passive diffusion are occurring. Complexation with DOC reduces the bioavailability of Cu and both Hg and MMHg such that bioaccumulation factors decrease with increasing organic content of the exposure medium.