Regulating Mercury Emissions from Power Plants: Will It Protect Our Health?
In a recent report, posted Friday, September 9th, the American Council on Science and Health (ACSH), concludes that the health benefits of a proposed regulation by EPA to reduce the mercury emission from power plants are not likely to be significant given the current data on the sources and health effects of environmental methylmercury levels.
While the ACSH report clearly states that about forty percent of the mercury released to air every year as a result of human activities in the US comes from electric power generation, this number is relativised by the statement that electricity generation contributes only 10 percent of total US mercury emissions when natural sources are included. Looking at the global scale, the report states that the US electricity generation contributes a mere 1 percent of total mercury emissions and Asia alone accounts for more than half of the world's mercury emissions. According to the data given in the report, human activities account for about 45 % of the global mercury emission (see figure above on the left).
Looking at bit closer at the given numbers, they do not seem consistent. The same report states that air levels of mercury have tripled since 1971 as the number of coal-burning plants worldwide has increased. How could such development be possible, if human activities account only for 45% of the total mercury emission?
Another argument outlined in the ACSH report is that methylmercury in sea fish presenting a health risk for human consumers is not linked to mercury in air but has its source in deep ocean sediments. This argument is totally missing the numerous reports on the mercury contamination of the US environment and its wildlife, and the nation wide fish advisories of nearly all US states (see EVISA News).
The report then presents some doubts that a real health risk for humans is existing, since the mean methylmercury concentration found in the blood of pregnant women in a CDC Survey in 2002 was in average 0.92 ppb, well below the so called "safety limit" set by EPA at 5.8 ppb. Such argumentation fails however to assess the risk for groups of the population, who do not behave as the mean because of their preference for fish meals. The ACSH report comes to the conclusion that with 6% of the women having methylmercury levels above the safety limit, "methylmercury levels in children and women of childbearing age are almost always below levels of concern".
As a final conclusion, the report summarizes that "most global mercury emissions come from human activities outside of the US. These emissions are likely to increase globally as more coal burning power plants are built. Because there appears to be little relationship between mercury emissions from US coal-fired plants and methylmercury exposure from eating fish, reducing US power plant mercury emissions-using either a "cap-and-trade" or MACT approach-should not be over-emphasized as a means of giving greater protection to pregnant women and children".
Of course one can argue whether the "cap-and-trade" or the MACT approach would be better suited to reduce the mercury emission of the USA. However one should bear in mind that it was the claimed "high efficiency" and "cost-benefit advantage" of the CAT approach that was used by the Bush administration to block a more global approach discussed by UNEP.
With 191 states being member of the United Nations, it is not surprising that each one contributes to the global mercury pollution only in the order of percent. Therefore, for fighting mercury pollution every member state has to do its homework. However, from a leading nation one would expect a leading role in the efforts to reduce the global pollution.
With respect to local "hot-spots", it is very likely that the distribution of mercury species being emitted from the power plants dictates whether mercury is entering the global pollution pool (export of the problem) or is being deposited close to the emission site. Speciation analysis therefore will play a major role in elucidating the atmospheric chemistry of mercury responsible for the deposition of mercury and its path entering the food-web.
Last but not least one should bear in mind that mercury pollution is not only a health risk for pregnant women and young children but for all life in the contaminated environment.
Prasad Pai, David Niemi, Bill Powers, A North American inventory of anthropogenic mercury emissions, Fuel Process. Technol., 65-66 (2000) 101-115. DOI: 10.1016/S0378-3820(99)00079-X
Paul F. Schuster, David P. Krabbenhoft, David L. Naftz, L. Dewayne Cecil, Mark L. Olson, John F. Dewild, David D. Susong, J.R. Green, M.L. Abbott, Atmospheric Mercury Deposition during the Last 270 Years: A Glacial Ice Core Record of Natural and Anthropogenic Sources, Environ. Sci. Technol., 36/11 (2002) 2303-2310. DOI: 10.1021/es0157503
C. Walcek, S. De Santis, T. Gentile, Preparation of mercury emissions inventory for eastern North America, Environ. Pollut., 123/3 (2003) 375-381. DOI: 10.1016/S0269-7491(03)00028-9
Christian Seigneur, Krish Vijayaraghavan, Kristen Lohman, Prakash Karamchandani, Courtney Scott, Global Source Attribution for Mercury Deposition in the United States, Environ. Sci. Technol., 38/2 (2004) 555-569. DOI: 10.1021/es034109t
C. Seigneur, K. Lohman, K. Vijayaraghavan, R.-L. Shia, Contributions of global and regional sources to mercury deposition in New York State, Environ. Pollut., 123/3 (2003) 365-373. DOI: 10.1016/S0269-7491(03)00027-7
Mercury speciation in the atmosphere and in stack gases
A. Carpi, Mercury from combustion sources: a review of the chemical species emitted and their transport in the atmosphere, Water, Air, Soil Pollut., 98 (1997) 241-254. DOI: 10.1023/A:1026429911010
S.E. Lindberg, W.J. Stratton, Atmospheric Mercury Speciation: Concentration and Behavior of Reactive Gaseous Mercury in Ambient Air, Environ. Sci. Technol., 32/1 (1998) 49-57. DOI: 10.1021/es970546u
Constance L. Senior, Adel F. Sarofim, Taofang Zeng, Joseph J. Helble, Mamani-Paco, Gas-phase transformations of mercury in coal-fired power plants, Fuel Process. Technol., 63/2-3 (2000) 197-213. DOI: 10.1016/S0378-3820(99)00097-1
Yewen Tan, Renata Mortazavi, Bob Dureau, Mark A. Douglas, An investigation of mercury distribution and speciation during coal combustion, Fuel, 83 (2004) 2229-2236. DOI: 10.1016/j.fuel.2004.06.015
S.E. Schober, T.H. Sinks, R.L. Jones, P.M. Bolger, M. McDowell, J.Osterloh, E.S. Garrett, R.A. Canady, C.F. Dillon, Yu Sun, C.B. Joseph, K.R. Mahaffey, Blood Mercury Levels in US Children and Women of Childbearing Age, 1999-2000, J. Am. Med. Assoc., 289/13 (2003) 1667-1674. DOI: 10.1001/jama.289.13.1667
Kathryn R. Mahaffey, Robert P. Clickner, Catherine C. Bodurow, Blood Organic Mercury and Dietary Mercury Intake: National Health and Nutrition Examination Survey, 1999 and 2000, Environ. Health Perspect., 112/5 (2004) 562-570. DOI: 10.1289/ehp.6587