Welcome to the University of Connecticut's Team Hg Web Page
Team Hg is a group of scientists and students associated with UConn's Department of Marine Sciences pursuing fundamental research into the biogeochemistry of mercury (Hg). Our focus has been understanding the mechanisms of Hg biological and chemical transformation and movement through the atmosphere, hydrosphere, cryosphere and surficial sediments. The Team's leader, Bill Fitzgerald, has been a pioneer in the study of Hg at the Earth's surface for over 25 years, and the Team's work has taken its members from volcanic fumaroles to polar ice, from atmospheric towers to deep lake sediments, and from Alaska's North Slope to New Zealand's Fjordland.
Mercury is a toxic trace metal, that may bioaccumulate in aquatic organisms and biomagnify to dangerous levels in the top trophic levels of fresh and saltwater food webs. The way in which Hg finds enters aquatic systems, and the biological and chemical transformations it may undergo are summarized in the following "cartoon":
Among our research goals is the understanding of the processes represented by the arrows in this diagram: the ways Hg is transformed in the environment. The most interesting and important of these processes are 1) reduction of ionic Hg to elemental Hg (Hgº) which results in Hg evasion from natural waters to the atmosphere, 2) scavenging of Hg by biological and mineral particulate matter, resulting in the accumulation of Hg in sediments, and 3) methylation of Hg by microorganisms, creating the highly toxic monomethyl and dimethylHg compounds. These processes "compete" with each other for the Hg present. Thus, greater reduction/evasion of Hg in a water body results in less Hg available to be methylated.
At the top of the figure, some aspects of the atmospheric chemistry of Hg are illustrated. Hg is present in the atmosphere as a vapor (a gas-phase form of a marginally volatile solid or liquid) of Hgº. This chemical form of Hg is long-lived in the atmosphere (average lifetime > 1 y) and may be dispersed globally as a result. Thus, sources of Hg to the atmosphere near and far contribute to the approximately 1-2 ng (ng=1 billionth of a gram) of Hg per cubic meter of air. The sources of Hg to the air are both natural (volcanoes and soil degassing) and human-related (coal and trash burning, cement production, chlor-alkai plants and many others). Once in the air, Hg may be oxidized and removed by rain or dust.
Once in fresh or saltwater, the ionic Hg has three fates. First, it may be removed from the water column through attachment to sinking particulate matter, and in this way become buried in sediment.
Secondly, some of the ionic Hg present in waters, and especially porewaters of sediment, may become methylated by microorganisms to form very toxic organomercury compounds (e.g., mono- and dimethylmercury). These organomercury forms can find their way into organisms at the bottom of a foodchain (bacteria and phytoplankton), and through the process of biomagnification be concentrated to hazardous levels in animals (including humans) that occupy the tops of those foodchains.
The third fate of ionic Hg in natural waters is to be reduced to elemental Hg (Hgº). This process appears to have both biological (bacteria) and abiological (photochemical) causes. This reaction can occur to such an extent that more Hgº may be formed in waters than can be balanced by Hgº in the air in chemical equilibrium. Such a chemical state is called "supersaturation" and if the water is stirred by wind, it results in the evasion of Hgº from lakes and the ocean to the atmosphere.
Therefore, some of the Hg released into the environment follows an air-water cycle: oxidation in the air and removal in rain -> reduction to Hgº in surface waters-> evasion to the air. One consequence of this cycling, is that Hg tends to have a longer "life" at the Earth's surface than many other pollutants, and it therefore has more opportunities to find its way to humans.
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