30% Ocean Mercury Rise Linked to Asian Coal Plants
World wide, 75 percent of human exposure to mercury is from the consumption of marine fish and shell fish. In the U.S., about 40 percent of all human exposure to mercury is from tuna harvested in the Pacific Ocean, according to Elsie Sunderland, a coauthor of the recent US Geologic Survey study.
Data used in this study comes from one of 15 (so far) research cruises that are part of a much larger, international project called CLIVAR; the Climate Variability (CLIVAR) Repeat Hydrography/CO2 research program.
Data analysis of the water samples indicated that total mercury levels in the North Pacific Ocean water have risen about 30 percent over the last 20 years.
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The authors attribute the rise to increases in global mercury atmospheric emission rates, particularly from Asia. “We believe the majority of Asian mercury emission comes from coal burning (for electricity generation),” stated William Landing, a marine scientist with Florida State University, one of the lead investigators for this study.
The data analysis results of water samples taken at 16 different sites (and at different depths) along the Eastern Pacific Ocean (from Hawaii to Alaska) indicate a significant increase (“bioaccumulation”) of a compound known as methylmercury (CH3Hg) which is far more toxic than mercury (Hg) alone. This increase occurs primarily between 200 and 700 meters below the surface, where, not coincidentally, the availability of dissolved oxygen (O2) drops off. This is because at that depth, naturally occurring bacteria proliferate as they decompose the “ocean rain” of dead, sinking algae, and use up a good deal of the O2 in the process. The Hg absorbed by the dead algae now combines chemically with a plentiful by-product of decomposition: methyl (CH3) molecules. These readily combine with mercury, forming MethylMercury. MethylMercury then works its way up the food chain (small invertebrates eat dead algae, they get eaten, etc) to larger fish, such as the Pacific Blue Fin tuna, which ends up in our sandwiches and sushi.
Since the beginning of the industrial revolution, it has been estimated that our air, water and soil have experienced a threefold increase in Mercury levels. Mercury, a soft, liquid-like, silverish metal (once known as “quick silver”) is toxic—especially to nerve cells–and becomes more dangerous when combined with methyl molecules, which are simple but ubiquitous organic compounds involved in a great number of biological/cellular processes (including gene silencing.). These molecules rapidly accumulate in organic tissue and can cause a variety of health problems. For example, Mercury has been shown to cause developmental defects in the human fetus. For this reason, in 2004, the EPA and FDA issued
the landmark Joint Guidance on the Consumption of Fish, which was specifically targeted towards pregnant women and nursing mothers.
Pregnant women are advised not to consume shellfish and marine fish. But this is more difficult in third world nations; for much of the world, marine fish and other sea foods are important parts of many peoples’ diets, as well as many animals. An estimated one third of the population of the planet derives part or all of its sustenance and/or livelihood from the sea. Thus, the important health and ecological questions of where the Hg comes from and how it ends up in fish at such high, contaminating levels have occupied ocean scientists for the past two decades.
Formerly, it was thought that the source of this marine mercury was from precipitation from the atmosphere polluted by coal burning power plants in Canada and the US. But these studies point to a more recent “enrichment” of the Eastern Pacific ocean. The apparent cause is emissions from fallout near the Asian coasts. USGS scientists surmise that the mercury-enriched waters then enter a long-range eastward transport by large ocean circulation currents.
To formulate this probable scenario, the scientists constructed a computer simulation that combined an ocean circulatory model with atmospheric emissions and Mercury transport and deposition data (including data from the water samples’ Hg levels).
The simulation also projects a 50 percent increase in Pacific Ocean mercury levels by the year 2050 based on published projections of increases in mercury emissions over the same timeframe.
The findings were published in the journal Global Biogeochemical Cycles.
Some of the sea food contributing to additional mercury exposure, according to the study, is swordfish, shrimp, Pacific pollock and Atlantic crabs.
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Very readable article. The mercury levels in the foodchain are out of control and will remain so for a long time. Governments all over the globe are recurring to coal fired powerplants, especially here in Chile, where they plan at least 14 large scale powerplants using coal along the coast. They had to find huge coal deposits to fuel these plants and they found it in Riesco Island, between Punta Arenas and Puerto Natales. To get to the coal they will destroy 7000 hectares of cold rainforest. I am concerned about the huge coal lobby that advertises coal as “clean”. And Chile does not care about increasing its carbon emissions. Who will stop them? They plan a coal powerstation 12 miles from a Humboldt Pinguin National Reserve, ignoring all international agreements to conserve the species.