WASHINGTON, May 6, 2009 - A landmark study by scientists from the U.S. Geological Survey (USGS) nd universities in the U.S. and Australia has, for the first time, documented how escalating mercury-laden air emissions, chiefly from coal-fired electrical power plants in Asia, are being transformed into methylmercury, a potent neurotoxin that is increasingly polluting the North Pacific Ocean and contaminating tuna, swordfish and other popular seafood.
The study, published May 1 in Global Biogeochemical Cycles (http://www.agu.org/pubs/crossref/2009/2008GB003425.shtml) , a scientific journal of the American Geophysical Union, predicts a 50 percent spike in the Pacific's mercury level by the year 2050 if mercury emissions from power plants increase according to current projections.
Mercury levels in fish risk children's health
Mercury exposure is especially dangerous to the fetus, newborn infants and young children during critical windows when the brain and other organs are rapidly developing.
Researchers have suspected for some time that emissions from coal-fired power plants in energy-hungry, rapidly industrializing China and India were a major environmental threat: according to the study, over the past two decades, emissions during the combustion of coal, which contains elemental mercury, have declined in North America and Europe, but "increased substantially" in East Asia and India. But exactly how airborne mercury from Asia has been entering deep ocean fish caught thousands of miles away has not been understood until now.
"Mercury researchers typically look skyward to find a mercury source from the atmosphere due to emissions from land-based combustion facilities," USGS scientist and coauthor David Krabbenhoft said in a statement. "In this study, however, the pathway of the mercury was a little different. Instead, it appears the recent mercury enrichment of the sampled Pacific Ocean waters is caused by emissions originating from fallout near the Asian coasts. The mercury-enriched waters then enter a long-range eastward transport by large ocean circulation currents."
In mid-depth ocean, the study showed, decomposing algae interact with mercury to form lethal methylmercury that enters the food chain, eventually contaminating tuna and other food fish.
EPA chief calls fish and mercury "major health threat"
The implications of the mercury cycle for human health are grave. According to the USGS, over 90 percent of human methylmercury exposure in the U.S can be attributed to consumption of ocean fish and shellfish. Pacific tuna consumption accounts for 40 percent of Americans' exposure.
Studies show that mercury exposure can alter brain development in the fetus, leading to learning problems, reduced performance on intelligence tests and other health problems later in life.
FDA under pressure to promote low-mercury fish
EPA's aggressive position on mercury contrasts sharply with that of the Food and Drug Administration (FDA), which has recently argued that the benefits of eating mercury-tainted seafood may outweigh the risks. FDA should reverse course and not only maintain but elaborate on the guidance it and EPA issued in 2004 (http://www.cfsan.fda.gov/~dms/admehg3.html) by adding more specific information about which low-mercury fish people can eat in place of species like tuna and swordfish, that tend to have elevated mercury levels.
The USGS study (http://www.doi.gov/news/09_News_Releases/050109.html) shows how mercury pollution from Asia can be expected to build up rapidly in the Pacific Ocean over the next few decades, in which case mercury contamination in the seafood consumed by millions of people would worsen dramatically.
EWG calls mercury in fish "clear and present danger"
"The prospect of ever-increasing levels of mercury in the Pacific Ocean and in tuna makes it even more urgent that FDA give the public more specific advice on fish that are safe to eat," said Jane Houlihan, Environmental Working Group (EWG) Vice President for Research.
"FDA should develop a list of low-mercury fish that women and other high-risk groups can eat without fear of ingesting significant amounts of mercury," Houlihan said. "FDA's new leadership should take immediate steps to protect the public health from the clear and present danger of mercury."
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