Mercury Levels in Yellowfin Tuna are Rising at a Staggering 3.8 Percent Per Year

You may want to rethink ordering that tuna. Scientists have found that mercury concentrations in Hawaiian yellowfin tuna are increasing at a staggering rate of 3.8 percent or more per year. This could cause major problems for the fish and those who eat them.

Mercury is a toxin that can accumulate in high concentrations in fish; this is largely due to what is known as bioaccumulation. Bioaccumulation means that the higher up the food chain a species is, the larger concentration of a particular toxin; algae absorbs the toxin, and then zooplankton eats the algae. Because a zooplankton eats a lot of algae, the toxin is concentrated. Then a small fish eats a bunch of zooplankton and the toxin is concentrated even further. The higher up the food chain you go, the more concentrated you find the toxin to be.

For decades, researchers have expected to see mercury levels in open-ocean fish increase in response to rising atmospheric concentrations. But evidence for this theory has been hard to find. That's why researchers decided to analyze yellowfin tuna, a fish that's high up in the food chain.

The scientists compiled and re-analyzed three previously published reports on yellowfin tuna caught near Hawaii. This revealed that the concentration of mercury in this species increased at least 3.8 percent per year from 1998 to 2008.

"The take-home message is that mercury in tuna appears to be increasing in lockstep with data and model predictions for mercury concentrations in water in the North Pacific," said Paul Drevnick, one of the researchers, in a news release. "This study confirms that mercury levels in open ocean fish are responsive to mercury emissions."

Mercury levels are actually increasing globally in ocean water. This means that fish like tuna, marlin and other large, predatory species are likely to feel the impacts.

"More stringent policies are needed to reduce releases of mercury into the atmosphere," said Drevick. "If current deposition rates are maintained, North Pacific waters will double in mercury by 2050."

The findings are published in the journal Environmental Toxicology and Chemistry.

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