Freshwater systems marine mammals

Most of the discrimination between inorganic and methylmercury thus occurs during trophic transfer, while the major enrichment factor is between water and the phytoplankton. This also has been reported for the diatom Thalassiosura weissflogii in a marine food chain (Mason et al. 1996). Methylmercury was accumulated in the cell cytoplasm, and its assimilation by copepods was 4 times more efficient than the assimilation of inorganic mercury. Bioaccumulation has been demonstrated for predator fish in both freshwater and marine systems and in marine mammals (see Section 5.4.4). Bioaccumulation of methylmercury in aquatic food chains is of interest, because it is generally the most important source of nonoccupational human exposure to this compound (EPA 1984b WHO 1990, 1991). 

The similarity in the effects of a given solute on homologous biochemical systems from species with widely different intracellular osmolalities is shown by the data in the upper-right panel of figure 6.3. Pyruvate kinase homologs from a mammal, freshwater clam, and both stenoha-line and euryhaline marine invertebrates show... 

If we consider the system in the eye of a marine fish we find the rhodopsin S3rstem as in birds and mammals and Invertebrates, but this is not the system to be found in the eyes of freshwater fish which contain another system. 

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