Re-emission of mercury

Of all the metals in the periodic table, mercury, Hg (atomic number 80), is the only one to exist as a liquid at ambient temperatures. Mercury is also volatile, which means that uncontained mercury atoms evaporate into the atmosphere. Today, the atmosphere carries a load of about 5000 tons of mercury. Of this amount, about 2900 tons are from current human activities, such as the burning of coal, and 2100 tons appear to be from natural sources, such as outgassing from Earth s crust and oceans. Since the mid-igth century, however, humans have emitted an estimated 200,000 tons of mercury into the atmosphere, most of which has since subsided onto the land and sea. It is probable, therefore, that a large portion of the mercury emitted from "natural" sources is actually the re-emission of mercury originally put there by humans over the last 150 years. 

SCRUDATO You talk about mercury Inputs to various aquatic systems, let s say coming in from the atmiosphere. But you didn t mention what, if any of the mercury, is going to be bound to organic or inorganic particulates, and how that adsorption-desorption processes would affect re-emission. The mercury, whether dimethylmercury or methylmercury, has a fair affinity for various types of particulate matter, I would imagine. How have you accounted for resorption-desorption in your consideration of re-emission of mercury back in the atmosphere ... 

Natural sources of mercury include volcanoes, evaporation from soil and water surfaces, degradation of minerals, and forest fires. It is estimated that today less than half of the global mercury emissions is due to natural sources (Fitzgerald et al. 1998, Jackson 1997, Lamborg et al. 2002, Coolbaugh et al. 2002). Although it is not possible to control natural emissions, it is important to mention that evaporation from soils may also include re-emission of Hg from previously contaminated sites. 

Natural emission and re-emission processes are particularly important for the mercury cycle in the environment. The distribution of mercury re-emission from soil in Europe is illustrated in Figure 4. The most significant re-emission fluxes are in Central Europe... 

Figure 4. Spatial distribution of mercury re-emission from soils in Europe.

Mercury emissions from European anthropogenic sources in 2002 totaled 180 tons this is 11 % lower than those in 2001. The input from natural emission and re-emission from European soils and the marginal seas is estimated at about 150 tons. More than 65% of emitted mercury was transported beyond the boundaries of Europe. The total mercury depositions to Europe were about 100 tons. Of this amount, 50 tons originated from anthropogenic sources of European countries the rest was the input from natural sources, re-emission and global anthropogenic sources. 

Ryaboshapko, A., Ilyin, I. (2001). Mercury re-emission to the atmosphere in Europe. In Proceedings of EUROTRAC Symposium 2000 Transport and Chemical Transformation in the Troposphere . 

Apparently monochromatic resonance radiation of mercury which passes through mercury vapor at the saturated pressure at 25 °C is about half absorbed in four millimeters distance. Beer s law is not obeyed at all because the incident radiation cannot be considered to be actually monochromatic, and absorption coefficients of mercury vapor vary many times between zero and very high values in the very short space of one or two hundredths of an Angstrom unit. Moreover, absorption of mercury resonance radiation by mercury vapor is sufficiently great even at room temperature to make radiation imprisonment a very important phenomenon. If the reaction vessel has any dimension greater than a few millimeters the apparent mean life of Hg(63P ) may be several fold the true radiative life of 1.1 x 10"7 sec, reaction (27), because of multiple absorption and re-emission. 

The natural global bio-geochemical cycling of mercury is characterized by degassing of the element from soils and surface waters, followed by atmospheric transport, deposition of mercury back to land and surface waters, and sorption of the compound to soil or sediment particulates. Mercury deposited on land and open water is in part revolatilized back into the atmosphere. This emission, deposition, and revolatilization creates difficulties in tracing the movement of mercury to its sources (WHO 1990). Particulate-bound mercury can be converted to insoluble mercury sulfide and precipitated or bioconverted into more volatile or soluble forms that re-enter the atmosphere or are bioaccumulated in aquatic and terrestrial food chains (EPA 1984b). 

Hg is relatively inert, but can be oxidized to Hg(II), particularly in the presence of chloride ions (Yamamoto 1996). Most surface waters are supersaturated with Hg relative to the atmosphere, and therefore elemental Hg is readily lost from the water to the atmosphere. It is suggested that the evasion of Hg from oceanic waters to the global atmosphere plays an important part in the global mercury cycle (Mason and Sullivan 1999, Fitzgerald and Mason 1996). Mason et al. (1994) estimated this re-emission from the sea to the atmosphere to be 2000 tons of mercury per year, and Lam-borg et al. (2002) estimated 800 tons per year. For many lakes, however, sedimentation of the Hg(II) and methylmercury bound to particulate matter is expected to be the dominant process for removal of mercury from the water column (Sorensen et al. 1990, Fitzgerald et al. 1991). 

It might finally be said that research in the last few years shows the mobility and possibility of air transport for mercury through re-emission to be greater than expected. This fact, coupled with the effect that low pH has on retention of mercury (with its subsequent effect on fish) could mean that, if acidification continues at the present rate in Sweden, thousands of additional lakes could be blacklisted within the next decade. 

The first observation of non-radiative excitation energy transfer was made by Cario and Franck [126]. They investigated Hg and Th vapor and illuminated with the resonance line of mercury and found emission spectra from both atoms although Thallium did not absorb the light from the mercury resonance line. Since radiation by re-absorption was not possible, only a non-radiative energy transfer could have been operative with the Hg atoms as donor (sensitizer) and the Th atoms as acceptors. 

Feathers exposed to the emissions within the Cu area were found to have very elevated concentrations of copper, arsenic and mercury. Arsenic is known to be a constituent of copper ores and can be easily converted to the volatile arsenic trioxide at smelting temperatures. The presence of large amounts of vanadium in crude oils that was reflected in the samples from the re/area is also well known. The concentrations of V in feathers were correlated with the distance of magpie territories from a certain section of the oil refinery (Dmowski and Golimowski, 1998). 

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