Bigeye tuna, or 'ahi, prized in Hawai'i for sashimi, contains higher levels of mercury than previously thought, according to revised data from the federal Food and Drug Administration.

The mean level of mercury in 'ahi, at .64 parts per million, approaches levels found in sharks, swordfish, tilefish and king mackerel, which the FDA recommends be entirely avoided by high-risk groups, which include children and women who may become pregnant, are pregnant or are nursing. Excess levels of mercury can pose a significant threat of neurological damage in infants and young children.

The Hawai'i Department of Health says its recommendation for limited consumption of ahi by those at risk is sufficient, but a national environmental group is urging the FDA to put bigeye tuna — the variety of 'ahi with the highest levels of mercury — on the no-eat list for people at risk.

"A single serving can cause a mercury exposure several times the EPA's recommended limit," said Eli Saddler, a University of Hawai'i graduate in public health and public health analyst for the Turtle Island Restoration Network's GotMercury program.

He said that it is important to distinguish between two species known in Hawai'i as 'ahi, since the bigeye can have twice the mercury levels of yellowfin, but "when you go into a restaurant and you ask what kind of 'ahi it is, they may not know."

STATE TESTS BACK FDA

The state Department of Health has seen the new data and has conducted its own tests at the Honolulu fish auction.

"The federal data are not news to us, and are in the range of levels we found in our own survey," said Dr. Linda Rosen, deputy state health director for health resources.

The state Department of Health recommends those in the risk group not eat shark, swordfish or shutome, and kajiki or Pacific blue marlin. It recommends no more than one meal every two weeks of opah, ono and 'ahi, and does not distinguish between the types of 'ahi — bigeye, tombo and yellowfin. It recommends no more than one meal weekly of lower-mercury fishes such as canned tuna, mahimahi and nairagi or striped marlin. It says you can eat as much as you like of the lowest-mercury fishes, such as akule, moi, mullet, salmon, squid and shrimp.

ASSESSING LIMITS

The EPA recommends expectant and nursing mothers and young children avoid entirely the highest-mercury fishes, and limit consumption to 12 ounces a week for all fish and shellfish.

Rosen said she considers the federal guidelines "a little too simple" for a fish-eating community such as Hawai'i, and feels consumers will be safe "if you stick to our recommendations."

Mercury is found naturally in the environment, but can build up in the food chain. As a result, the top predators get higher levels than creatures eating lower on the food chain. Sharks, swordfish and tuna are among the top predators.

LEVELS VARY

The amount of mercury in a particular fish depends on what it's been eating, as well as its age and size. In general, older and bigger fish have higher levels of mercury than younger, smaller fish, but that's not always a safe assumption, Rosen said.

"We did find the highest levels of mercury in a 213-pound 'ahi, and half that level in a 246-pounder," she said.

Saddler said European countries, Japan and Canada all have much stricter standards for mercury in fish than the United States does.

"In Europe, they test each batch of fish, and if levels are too high, they pull it off the market," he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.