Study shows mercury concentrations in Hawaii-caught tuna on the rise

Updated: Mar. 7, 2017 at 2:52 PM HST
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HONOLULU (HawaiiNewsNow) - Eat ahi?

Then you'll want to pay attention to a new study that shows mercury concentrations in Hawaii-caught bigeye and yellowfin tuna are steadily rising.

The research, published this week in an online version of the journal Environmental Toxicology and Chemistry, found that mercurcy concentrations in yellowfin tuna increased by about 5.5 percent a year from 1998 to 2008, while levels in bigeye tuna grew by about 3.9 percent from 2002 to 2008. (Bigeye tuna tend to have higher mercury concentrations than yellowfin tuna.)

"This paper confirms our previous work showing that mercury concentrations in yellowfin tuna caught near Hawaii are increasing, and it demonstrates that the same phenomenon is happening in bigeye tuna," said lead author Paul Drevnick, in a news release.

Yellowfin and bigeye tuna are marketed as ahi and are widely used in raw fish dishes or for grilling.

In January, the FDA and EPA added bigeye tuna to its list of fish to be avoided by pregnant women, women who might become pregnant, breastfeeding women and young children.

The good news: For both bigeye and yellowfin tuna, Drevnick and co-author Barbara Brooks, of the state Health Department, found that mercury concentrations in fish tissue rarely exceeded the FDA's "action level" of 1 part per million of methylmercury in an edible portion.

"The FDA action level is defined as 'a limit at or above which FDA will take legal actions to remove products from the market,' and according to the limit and the data here, no action should be taken," they wrote.

The EPA, meanwhile, has a "fish tissue residue criterion" for methylmercury that applies to freshwater and estuarine fish and shellfish but not to marine fish such as tuna. Even so, the authors note that the average mercury concentrations for both yellowfin and bigeye now exceed the EPA criterion and that "consumers of yellowfin tuna and bigeye tuna caught in the North Pacific are not protected from adverse effects of mercury."

Researchers believe the rise in mercury concentrations in Hawaii fish is linked to atmospheric mercury emissions from Asia.

Mercury is a toxic trace metal that can accumulate to high concentrations in fish.

In North Atlantic waters, mercury concentrations peaked in the 1990s and are now declining thanks to environmental regulations.

But in the North Pacific, mercury concentrations in waters shallower than 1,000 meters increased about 3 percent per year between 1995 and 2006 and are expected to double by 2050 if current mercury deposition rates are maintained, Drevnick reports.

"The temporal trend in mercury concentrations in these waters is mirrored by the changes in mercury concentrations in yellowfin and bigeye tuna caught near Hawaii," Drevnick said. "For that reason, future monitoring efforts should include these species from this location."

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