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METAALICUS – stands for Mercury Experiment To Assess Atmospheric Loading In Canadá & the United States Now under way at the Experimental Lakes Area (ELA) in northwestern Ontario, Canada. Its goal is to understand the link between atm Hg deposition & accumulation of METHYLMERCURY in FISH. Along the way, a better understanding should emerge of what happens to Hg that’s added to the envi ronment because of human activity. Despite decades of research, the transformations of Hg in the environment are not yet fully understood. The greatest concern with Hg POLLUTION is Me-Hg, a organic form of Hg produced by SULFATE-REDUCING BACTERIA from inorganic Hg. Me-Hg accumulates in the food chain & reaches humans other mammals & birds through Me-Hg-tainted fish. In humans, Me-Hg reduces motor skills & dulls the senses of touch, taste, & sight. In severe cases, it causes irreversible brain damage & even death. At greatest risk are UNBORN & YOUNG CHILDREN. Both the Environmental Protection Agency & Food & Drug Administration Are advising women who are pregnant or of childbearing age, nursing mothers & children to limit consumption of FISH that may contain high levels of Hg. Because of the health effects of methylmercury, EPA announced on 14.12.2000, that it will regulate Hg emissions from COAL- & OIL-FIRED POWER PLANTS. The agency is scheduled to propose regulations by 15.12.03 & to issue final regulations by Dec. 15.2004. Existing power plants will have until 2007 to comply, but power plants installed after the regulations are in place will have to comply IMMEDIATELY. According to EPA, coal-fired power plants are the largest source of anthropo genic Hg emissions in the U.S. WASTE INCINERATORS, such as municipal waste combustors, medical waste incinerators & hazardous waste combustors are also significant sources, says Kuzmack Arnold M., senior science adviser to EPA’s Office of Water He adds that emissions from disposal of Mg-contg prodts – such as thermo meters, thermostat switches, & fluorescent bulbs – are controlled by emission standards set by EPA for incinerators & combustors. Likewise, emissions & water releases from Hg-requiring processes, such as chlor-alkali production, are generally well controlled. “The biggest remaining source we know that’s unregulated is coal-fired power plants. Even as coal- & oil-fired power plants face the prospect of spending on emissions control technology, it’s not clear where the Hg in fish comes from. Part of the Hg in the environment stems from emissions to the atmosphere by natural sources. Part comes from reemission of so-called old Hg – Hg bound in soils & sediments that originates from past natural & anthropgenic emission Old Hg also includes Hg already present in soil & sediments. And part comes from new emissions caused by human activity. Regulations would affect only the latter – “new” mercury. “Billions of dollars potentially could be spent to regulate mercury”, points out METAALICUS coordinator Harris Reed C., senior environmental engineer at Tetra Tech Inc., Oakville, Ontario “But nobody knows for sure what will happen to fish mercury if you change the amount coming out of the sky” METAALICUS was designed to answer this fundamental question. It will also establish the importance of Hg deposited directly to the lake & that deposited to the lake’s surroundings. The experiment involves adding NONRADIOACT IVE STABLE ISOTOPES of inorganic Hg to one lake at ELA – Lake 658 – and to the UPLAND & WETLAND areas that make up its watershed. THREE ISOTOPES are being used: 198Hg for the wetland, 200Hg for the upland & 202Hg for the lake. The entire ecosystem 129.2 acres altogether, will receive added Hg at a rate of < 13 g/year. That’s equivalent to the amount of wet deposition received by the most atmospherically polluted lakes in eastern North America, says METAALICUS senior adviser Rudd John W.M., a microbiologist at Canadian Dept of Fisheries & Ocean The total amount that will be added to the ecosystem is about half a teaspoon of Hg, to be applied in the form of Hg(II) over 3 years. Applications for this Year began in June & will be completed in October. Enough isotopes have been purchased, from Russia, for the first 2 years of the project. The team is still raising funds to purchase the third year’s isotopes. Altogether the 3-year supply of isotopes costs $500,000. The experiment has become possible only recently, when MASS SPECTRO METERS that are sensitive enough to measure the excess produced by the added isotopes over the natural background became available. The fates of the isotopes will be trackede through various parts of the ecosystem by U.S. & Canadian scientists, led by 22 principal investigators who are, many say, second to none among experts on Hg in the environment “For the past 2 years, the research team has been carrying out pilot studies in terrestrial & aquatic conditions to ensure that the new analytical methods & approach would work when the study went full scale” Harris says. For example, the group led by Branfireun Brian, a hydrologist from University of Toronto, Missisauga Has been addressing questions of methodology & process in the upland & wetland through controlled pilot-scale studies. The first very important question that we had to address was a analytical one: If we apply these Hg isotopes in small amounts, will we be able to see them in the environment at the whole-ecosystem scale?. And once the Hg is applied, how will it move & at what rate? How much will be bound in, for example the peat in wetlands? Wetlands, he explains, often are intervening features between upland terrain & lakes in forests & could be key sites of Hg transformation. It’s important to determine if the applied isotopes simply would accumulate in peats, like many other metals & pollutants, or if they would be transformed into methylmercury & transported downstream into the aquatic ecosystem. “The preliminary results of the pilot-scale studies have allowed us to proceed to the whole-ecosystem experiment with confidence” Launching the full-scale experiment took a while. Pilot-scale studies & preli minary experiments in isolated plots had to be done. And getting permi ssions from different levels of government for the full-scale experiment took more than 3 years. “We knew that the amount of Hg we would be adding would not be toxic to the ecosystem, but we had to convince & assure people who were giving us permission that we knew what we were doing. It was a tremendous effort to get approval”. The isotopes for the upland & wetland must be applied by aircraft during a rainstorm, & that operation proved tricky initially. “I had to use 3 different phones at the same time. When it looked like we’d have rain in the next 5 minutes, I’d call the pilot & he’d take off” But if it didn’t rain after all, the pilot couldn’t land the plane loaded with the 500 L of water. If the isotopes had already been mixed in this water, the pilot would have had to dump about $70,000 worth of cargo. So, a injection system had to be installed so that the pilot would add the isotopes to the water only when rain was a certainty. With logistics & permissions in place, the whole-ecosystem study of Lake 658 has been under way since June. “I have collectors underneath the forest canopy to see how much of the isotop es makes it through” says Louis Vincent L. St., watershed ecologist from the University of Alberta He leads the team that’s studying the effect of the forest canopy on Hg deposi tion. His team also is collecting litter fall & ground vegetation to see how much of the isotopes is incorporated into plants. “We’re trying to determine whether the Hg in plants is the new Hg added to the ecosystem or Hg that’s just being recycled around” The team led by Hurley James P., aquatic chemist & assistant director for research at the Water Resources Institute, University of Wisconsin, Madison, will be studying rates of Hg recycling at the sediment-water interface in the lake. “We typically see buildup of Hg in the deeper waters of lakes during summer & fall”. “This study will allow us to determine if this is due to recycling from recently fallen particles or from the historical pool of Hg in the sediments” “We want to know whether the Hg in fish this year is the Hg that got deposited this year or the Hg deposited years past”, says Gilmour Cynthia C., biogeochemist & associate curator at the Academy of Natural Sciences Estuarine Research Center She leads one of the teams that’s working on Hg methylation. She’s especial lly interested in how Hg gets into cells& how Hg’s complexation chemistry affects that process. “The working hypothesis is that new Hg would be more mobile & more bioavailable than old Hg. According to Lindberg Steven E., a corporate research fellow at Oak Ridge National Laboratory’s Environmental Science Div., “People have hypothesize d that new Hg might be more photochemically reactive, might be more readily photoreduced & might bind to organic matter more tightly” His group is responsible for air-surface exchange studies, making Hg flux measurement over the lake, the wetland, & the upland to determine gow much of the Hg isotopes are being emitted from various surfaces. Preliminary data from a pilot-scale study indicate “a initial important different ce in the reactivity & behavior of freshly deposited Hg” But the difference seems short-lived “Within days to weeks, the new Hg behaveslike old Hg” METAALICUS provides opportunity to fill gaps in the understanding of Hg cycling. Among questions researchers still don’t have good answers for are: Why are wetlands good in producing methylmercury? What is & what controls the amount of Hg in lakes that is available to microorganisms for methylation? How important are photochemical reactions on the lake surface to methylmercury production? “We have people working on those kinds of questions”, Harris says One of the outcomes from METAALICUS would be basic data such as rates of & factors governing methylation, redn of inorganic Hg & uptake of methyl mercury. “These will be used to fine-tune models so we can make better predictions. |
| UPDATE | 09.01 |
| AUTHOR |
Academy of Natural Sciences Estuarine Research Center. Gilmour Cynthia C. biogeochemist & associate curator Canada – Federal Government Environmental Canada Fisheries & Ocean Dept., Rudd John W.M., microbiologist & MET AALICUS sr adviser Forest Service National Sciences Engg. & Research Council Electric Power Research Institute. Carlton Richard G. manager of quantitative ecology Tetra Tech Inc., Harris Reed C., sr. environmental engineer & METAALICUS coordinator University Alberta. Louis Vincent L. St. watershed ecologist University Toronto, Missisauga. Branfireun Brian, hydrologist University Wisconsin, Madison Water Resources Institute. Hurley James P., aquatic chemist & assistant director for research at Institute US Government – Energy Dept US Government – Environmental Protection Agency Office of Water, Kuzmack Arnold M., sr. science adviser US Government – Food & Drug Administration US Government – Geological Survey US Government – Oak Ridge National Laboratory. Environmental Sciences Division. Lindberg Steven E., corporate research fellow Wisconsin Dept of Natural Resources |
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