Big fish

Pacific ocean fish battling the surge of radioactive sludge leaking from the Fukushima meltdown also face another threat according to a new study published in the journal Nature Geoscience. Mercury levels in Pacific fish are on the rise as a result of pollution from coal plants in India and China.

According to the Los Angeles Times, researchers from the universities of Hawaii and Michigan examined mercury levels in nine species of fish common in the North Pacific Subtropical Gyre,  ”the largest ecosystem on the planet, at 7 million square miles.”

Deep ocean fish, such as tuna, showed higher levels of mercury contamination than the fish species who swim closer to the surface. “Sunlight breaks down the kind of mercury that’s dangerous on the sushi platter: monomethylmercury,” reports the Times.

But where is all the mercury coming from?

The researchers looked at the “fingerprint” of the mercury, which the team concluded was a result of atmospheric mercury—meaning the result of industry and more specifically, coal plants, which are on the rise in both India and China.

“The surprising thing is that when we remove this fingerprint of organic mercury, we get a match between elemental mercury in the atmosphere and the isotopic compositions in fish,” Brian Popp, a University of Hawaii geochemist who was part of the research team told the Times. “People have speculated that the main source of mercury to the ocean is through atmospheric deposition, but people have also argued that it comes from sediments, hydrothermal activity, coastal sediment that’s moved from the coast to the open ocean. Our work suggests the main source is from the atmosphere.”

Marine microbes seem to be the cause for the high mercury levels in the deep sea fish populations, reports the Times. “About 80% of the organic mercury in the tissue of fish from the deep probably was produced by these bacteria clinging to sinking particles of organic matter.”

Keep in touch with Jill on Twitter @jillettinger

Image: sanberdoo