Ocean Mercury on the Rise - Oceana USA
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May 5, 2009

Ocean Mercury on the Rise

BY: kim

In a remarkable new study, scientists have uncovered a link between human emissions of mercury and contamination of marine fish. What’s more, Pacific Ocean mercury levels are on the increase and are predicted to double by the year 2050 unless we can control human mercury emissions.Although we have known for some time that humans have caused a 200-400% increase in the amount of mercury circling the globe, it was unclear how and where in the ocean that mercury got transformed to the more toxic methylmercury that contaminates fish. The fishing industry favored the hypothesis that all the mercury in ocean fish is “natural”, derived from deep ocean vents—a view adopted recently in California courts. Meanwhile, other scientists have shown that methylmercury can also be made in coastal and ocean shelf sediments from mercury released by humans on land, similar to the process in freshwater systems. But this new study shows that methylmercury can also be made in the ocean water column, right along the low oxygen boundary between the upper and deep ocean, where sinking particles gather, from mercury that has been transported in ocean currents from land-based pollution in Asia. The authors calculate that it only takes about four years for human-released mercury from the coast of Asia to reach the Eastern North Pacific (above Hawaii) traveling on these currents.Now scientists have revealed two different pathways for human-based mercury pollution to contaminate marine fish—through coastal sediment and open ocean processes. While this strong evidence would seem to rob the fishing industry of one of their favorite arguments—that all mercury in ocean fish is from natural sources—it should be a cause for optimism. The encouraging news is that if we act now to eliminate needless mercury emissions from sources such as chlor-alkali plants today, we can expect to see decreases in ocean fish mercury levels in the not too distant future.[Kim Warner is a marine scientist for Oceana’s Stop Seafood Contamination campaign.]