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Mercury levels in oceans double or triple those of the past

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Mercury levels in the oceans of the world are rising, increasing by two to three times as much as the levels present at the start of the Industrial Revolution, a recent study indicates.

Data gathered during 12 sampling cruises conducted in the last eight years has provided a first direct computation of the levels of mercury pollution in the world's oceans, researchers conducting a study funded through the U.S. National Science Foundation and the European Research Foundation say.

"Mercury is an environmental poison that's detectable wherever we look for it, including the ocean abyss," says Don Rice, director of the NSF's Chemical Oceanography Program.

The study, involving scientists from the United States, France and the Netherlands, has been published in the journal Nature.

Mercury created by human activity, including burning fossil fuels and mining for gold, is more abundant in the world's ocean than previously thought, the researchers say.

Inorganic mercury enters the marine food chain as toxic methylmercury, which if consumed by humans via seafood can lead to nervous system damage.

Mercury levels in the ocean vary by depth, normally elevated more at the sea surface than in deeper waters, the researchers found, but high levels in the North Atlantic were detected at more than 3,300 feet deep.

Until the study little had been known about how much of the mercury in our environment was the result of human activity, the researchers said.

"It would seem that, if we want to regulate the mercury emissions into the environment and in the food we eat, then we should first know how much is there and how much human activity is adding every year," said study leader Carl Lamborg of the Woods Hole Oceanographic Institution in Massachusetts.

Previously there had been no way to take water samples and detect the difference between mercury coming from pollution sources and mercury with a natural source, says Lamborg, who has studied mercury in the environment for 24 years.

"Now we have a way to at least separate the bulk contributions of natural and human sources over time," he said of the new study.

The study results were in general agreement with levels of mercury pollution previously estimated through computer modeling, the researchers said, yielding a figure of 60,000 to 80,000 tons of mercury in the world's oceans.

With current human activity, the same amount of mercury could be added in the next 50 years as has been seen in the last 150 years, Lamborg said.

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