Mercury cycle, complexity

High body burdens of mercury normally encountered in some species of fish and wildlife from remote locations emphasize the complexity of natural mercury cycles and human impacts on these cycles... 

Mercury provides an excellent example of the importance of metal speciation in understanding biogeochemical cycling and the impact of human activities on these cycles. Mercury exists in solid, aqueous, and gaseous phases, and is transported among reservoirs in all these forms. It undergoes precipitation-dissolution, volatilization, complexation, sorption, and biological reactions, all of which alter its mobility and its effect on exposed populations. The effect of all... 

Schetagne R, Verdon R. 1999. Post-impoundment evolution of fish mercury levels at the La Grande complex, Quebec, Canada (from 1978 to 1996). In Lucotte M, Schetagne R, Therien N, Langlois C, Tremblay A, editors. Mercury in the biogeochemical cycle. Berlin, Germany Springer, p. 235-258. 

Hawthorne and co-workers have also produced a series of macrocyclic Lewis acid hosts called mercuracarborands (156, 157, and 158) (Fig. 84) with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers. They were synthesized by a kinetic halide ion template effect that afforded tetrameric cycles or cyclic trimers in the presence or absence of halide ion templates, respectively.163 These complexes, which can bind a variety of electron-rich guests, are ideal for catalytic and ion-sensing applications, as well as for the assembly of supramolecular architectures. 

Because of the complex cycling of MMHg in the ocean, carnivorous fish at the top of the food chain could be naturally enriched in mercury. But mercury levels in seabird feathers show significant increases over time, suggesting that anthropogenic emissions have similarly caused an increase in fish tissues. 

Amongst other ICC with five-link metal-cycles, we note o-indoline 877 (X = NTs) [160-163] and o-indophenol 877 (X = 0) [163,172,173] chelates, obtained in reaction (4.47). According to the expected results, palladium complexes of the type discussed are planar, while the ICC of zinc, mercury, and lead are tetrahedral [161,172,173],... 

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