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UPTAKE, TOXICITY, AND TROPHIC TRANSFER OF MERCURY IN A COASTAL DIATOM. (R824778)
Citation:
Mason, R. P., J. R. Reinfelder, AND F. M. Morel. UPTAKE, TOXICITY, AND TROPHIC TRANSFER OF MERCURY IN A COASTAL DIATOM. (R824778). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 30:1835-1845, (1996).
Description:
The primary mechanisms controlling the accumulation of methylmercury and
inorganic mercury in aquatic food chains are not sufficiently understood.
Differences in lipid solubility alone cannot account for the predominance of
methylmercury in fish because inorganic mercury complexes (e.g.,
HgCl2), which are not bioaccumulated in fish, are as lipid soluble as
their methylmercury analogs (e.g., CH3HgCl). Mercury concentrations
in fish are ultimately determined by methylmercury accumulation at the base of
the food chain, which is governed by water chemistry, primarily pH and chloride
concentration. Our studies of mercury speciation, toxicity, and phytoplankton
uptake demonstrate that passive uptake of uncharged, lipophilic chloride
complexes is the principal accumulation route of both methylmercury and
inorganic mercury in phytoplankton. The predominance of methylmercury in fish,
however, is a consequence of the greater trophic transfer efficiency of methyl-
mercury than inorganic mercury. In particular, methylmercury in phytoplankton,
which accumulates in the cell cytoplasm, is assimilated by zooplankton four
times more efficiently than inorganic mercury, which is principally bound in
phytoplankton membranes. On the basis of these results, we constructed a simple
model of mercury accumulation in fish as a function of the overall octanol-water
partition coefficient of methylmercury. Our model can explain the variability of
mercury concentrations in fish within, but not among, different lake regions.