Mercury Transport and Speciation

The global mercury cycle involves mercury release from geological and industrial processes into water and the atmosphere, followed by sedimentation via rainfall and by microbial metabolism that releases mercury from soil and sediments and transforms mercury from one chemical form to another. 

Atmospheric-home mercury, including anthropogenic mercury is deposited everywhere including remote areas of the globe, hundreds of kilometers from the nearest mercury source, as evidenced by its presence in ancient lake sediments and glacial ice. In Amituk Lake in the Canadian Arctic, recent annual deposition of mercury was estimated at 15.1kg, about 56% from snowpack, and the rest from precipitation. This represents a dramatic increase from historic annual burdens of 6.0 kg of mercury aimually in this remote area the effects of this increase on Arctic watersheds are unknown. 

Mercury speciation varies in atmospheric, aquatic, and terrestrial enviromnents. In the atmosphere, mercury is in the form of gaseous elemental Hg (95%), Hg + (called reactive gaseous mercury), and trace amounts of methylmercury. Particulate and reactive mercury in the atmosphere travels short distances, usually less than 50 km, and has a residence 

Sulfate-reducing bacteria are the most important mercury-methylating agents in aquatic environments, with the most important site of methylation at the oxic-anoxic interface in sediments a similar pattern is documented for wetlands. In sediments, miao-bial methylation of mercury is fastest in the upper profiles where rate of sulfate reduction 

Additional research is recommended on inorganic mercury-Ugand formation in water and runoff and its effects on methylmercury formation in soils, and on quantification of the sources and transport characteristics of methylmercury in terrestrial environments. The mercury-Ugand form exiting the terrestrial watershed wiU strongly influence the mercury/methylmercury bioaccumulation potential in surface waters. Accordingly, more analyses are needed to determine the mercury 

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Suer, P., and Allard, B. (2003). Mercury transport and speciation during elctrokinetic soil... 

Research characterizing mercury speciation is an essential first step in the development of models to predict its transport and fate on regional and global scales. This review illustrates that several key global issues are likely to have major impacts on the speciation of mercury. These include (i) climate change, (ii) ozone depletion, and (ii) changes in topography. 

Mercury and lead serve no known biological function, but both are useful metals and employed by mankind since ancient times. Both are also toxic environmental contaminants and thus of prime concern for several governmental agencies. AU this has led to intense research on the biogeochemistry of mercury and lead, including their speciation in the environment, their atmospheric transport, and the processes affecting their fate these topics and more are summarized in Chapters 9 and 10. 

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... 

Gray JE, Theodorakos PM, Bailey EA, Turner RR. 2000. Distribution, speciation, and transport of mercury in stream-sediment, stream-water, and fish collected near abandoned mercury mines in southwestern Alaska, USA. Sci Total Environ 260 21-33. 

Chemical speciation is especially critical when assessing mercury toxicity. Metallic mercury, because of its volatility, presents a hazard that seems to undergo repeated rediscovery. Its ability to seep into fissures in surfaces such as floors, from which it volatilizes, often leads to neglect of necessary precautions because it is not visible. Mercury vapor also reaches the brain far more readily than the ionic forms. Since the conversion of elemental mercury to mercuric ion by blood is a slow process compared to the time required for transport from lung to brain, and since elemental mercury seems to penetrate readily into brain,CNS tissue may contain ten times more mercury after vapor exposure than after a comparable intravenous dose of mercuric salt. The mercury is then retained in brain after oxidation because the... 

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