Big increase in ocean mercury found; study predicts more human threat from fish
Mercury in ocean will rise by 50 percent as emissions from coal-fired power plants increase, study says. U.S. scientists document for first time how mercury from industry gets into seafood.
By Marla Cone
Environmental Health News
May 2, 2009
Mercury levels in the Pacific Ocean will rise by 50 percent within the next few decades as emissions from coal-fired power plants and other sources increase, scientists reported Friday.
As a result, people around the globe could be increasingly exposed to mercury from eating fish and other seafood. Methylmercury, a neurotoxin, can alter brain development of fetuses and has been linked with learning problems and reduced IQs in some children.
The research team also documented for the first time how mercury from industrial sources contaminates seafood.
For decades, scientists have tried to explain whether the methylmercury in ocean fish is natural or manmade, with some saying it originated in the ocean. USGS geochemist David Krabbenhoft and his colleagues discovered that industrial emissions are transformed into methylmercury in mid-depth ocean waters.
"This study gives us a better understanding of how dangerous levels of mercury move into our air, our water, and the food we eat, and shines new light on a major health threat to Americans and people all across the world,” U.S. Environmental Protection Agency Administrator Lisa P. Jackson said in a statement.
The scientists reported that algae filtering down to the mid-ocean depths of 200 to 700 meters is decomposed by bacteria, which “methylates” the industrial mercury, turning it into methylmercury, a form that can be taken up by marine life. The methylmercury then moves up the food web, from species to species.
The new findings are “critically important to the health and safety of the American people and our wildlife because it helps us understand the relationship between atmospheric emissions of mercury and concentrations of mercury in marine fish,” Interior Secretary Ken Salazar said in a statement.
“We have always known that mercury can pose a risk, now we need to reduce the mercury emissions so that we can reduce the ocean mercury levels,” Salazar said.
A spokesperson for the fishing industry, Mary Anne Hansan of the National Fisheries Institute, said the researchers did not test levels of mercury in fish, only ocean waters, "which renders any conclusions or forecasts about seafood incomplete and irresponsible."
"This study deserves hard scrutiny, especially because existing, peer-reviewed research shows no mercury increase in ocean-going fish over the last 30 years," she said.
The findings were based on mercury samples from 16 locations in the North Pacific, including waters off Alaska and Hawaii, according to the article published in a journal of the American Geophysical Union called Global Biogeochemical Cycles.
|The study’s lead author, Elsie Sunderland, of Harvard University’s Atmospheric Chemistry Modeling Group, reported in 2007 that 40% of people’s exposure to methylmercury in the United States comes from tuna. While some fish are more highly contaminated, tuna is the most widely consumed fish.|
40% of people’s exposure to methylmercury in the United States comes from tuna.
The U.S. Food and Drug Administration advises pregnant women, nursing mothers and women who may become pregnant to limit their fish and seafood consumption to two, 6-ounce meals per week. They should avoid all consumption of shark, swordfish, king mackerel and tilefish, and no more than one of the weekly meals should be albacore or white tuna, the FDA says.
About 6% of U.S. women, or about 3.8 million people, exceed the amount of mercury that the EPA says is safe for fetuses.
Krabbenhoft, Sunderland and their colleagues said it’s not too late to avoid the projected increase in ocean mercury.
Since they found that mercury levels in the vast ocean can increase so rapidly, they said it is also likely that the levels would decrease rapidly if emissions are reduced.
Asia’s burning of coal is the primary source of mercury emissions worldwide.
The scientists said they were surprised to discover that much of the mercury is circulated over vast distances via the ocean, not the air. The emissions fall to the ground near the Asian coasts, then are transported eastward by ocean currents, Krabbenhoft said.
The study is available at http://www.agu.org/pubs/crossref/2009/2008GB003425.shtml
Details of the report are available from the USGS at http://toxics.usgs.gov/highlights/pacific_mercury.html