News Coverage
Small tuna found to hold less mercury
A study finds wide variation between West Coast albacore and larger fish in big brands
Published February 10, 2004
Sharply varying levels of mercury in tuna are complicating efforts by healthauthorities to get straight advice to consumers, especially pregnant womenand young children who are most vulnerable.
Researchers at Oregon State University have found mercury concentrations in a sample of 91 albacore tuna caught off the West Coast to be about half the level cited by the U.S. Food and Drug Administration as typical of canned store brands or fresh albacore steaks.
Their findings, presented at a recent scientific meeting in San Diego, underscore the difficulty facing health authorities as they try to clarify confusion about the risks of mercury.
"Trying to apply a generic warning, a one-size-fits-all approach, that's very challenging," said William Lambert, an environmental epidemiologist at Oregon Health & Science University's Center for Research in Occupational and Environmental Toxicology.
"There is a considerable amount of variation from place to place, and from species to species, which we didn't appreciate before," said Lambert, who was not involved in the OSU study. "That increases the challenge to regulators."
Smaller size is what makes the difference in West Coast albacore, said Michael Morrissey, director of OSU's Sea Food Laboratory in Astoria, which performed the study with money from two fishing industry groups.
Oregon and other coastal tuna fishing boats use surface hook-and-line gear to catch smaller, 10- to 25-pound fish, compared with 40- to 60-pound albacore caught in the South Pacific that are used by name-brand tuna canners, Morrissey said.
West Coast albacore are sold fresh off the boat in many ports, and small canneries that have sprung up in Oregon and Washington are selling the fish for about $3.50 to $4 a can at gourmet groceries and health food stores.
Jane Houlihan, vice president for research at the Environmental Working Group, an advocacy group in Washington, D.C., said the information doesn't help the average shopper.
"The consumer can't look at a can of tuna and decide how big a fish it was," Houlihan said.
Sources of mercury Mercury, a naturally occurring element that also is emitted from coal-burning power plants and waste incinerators, accumulates over time in the flesh of tuna and many other large, long-lived predatory fish of the open ocean.
Concentrations of mercury in several fish species are high enough to harm pregnant women and young children. Mercury can pass from a woman to her fetus and interfere with brain development, causing a range of problems, from learning disabilities to mental retardation.
The U.S. Food and Drug Administration in 2001 began advising women of childbearing age, pregnant women and nursing mothers to avoid eating shark, swordfish, king mackerel and tilefish, the species with the highest known concentrations of mercury. The FDA said eating a variety of other fish, limited to two or three servings a week, is a good rule for pregnant women.
Agency draws fire Many consumer groups immediately criticized the agency for placing tuna among all other fish deemed generally safe for pregnant women.
"They still aren't giving people clear information about how much tuna is safe to eat," Houlihan said. "When we look at the numbers, we recommend that women steer clear of albacore tuna altogether."
Many scientists and health authorities consider that advice too strong. Morrissey, for instance, said mercury levels in the West Coast albacore he tested were comparable to levels in "light" canned tunas, which are made with a smaller type of tuna called skipjack.
"The risk is, what message does the consumer walk away with -- maybe I shouldn't eat fish?" Morrissey said.
That risk was found real by researchers at Harvard University who studied eating habits of pregnant women after the government's 2001 mercury warning. Women reduced consumption of all types of fish, including types with low mercury levels. Given the nutritional benefits of fish, the researchers concluded that the public health benefits of the dietary changes are uncertain.
Seafood advisory In response to outside critics and its own advisory group, the FDA began rewriting its seafood advisory. The agency said it wants to be more specific and consistent with the risk analysis done by the U.S. Environmental Protection Agency. An advisory committee has told the FDA to develop guidelines for canned tuna, based on a detailed analysis of what contribution canned tuna makes to mercury levels in women.
The FDA and EPA estimate that 8 percent of women of childbearing age have unsafe levels of mercury exposure.
In the OSU study, sponsored by the Oregon Albacore Commission and the Western Fishboat Owners Association, Morrissey and colleagues tested 91 albacore tuna caught off the West Coast from Southern California to British Columbia. The average mercury concentration was 0.14 parts per million, less than half the 0.36 parts per million the FDA reports as typical of canned albacore tuna.
"For someone who is trying to limit their intake of mercury, that is a meaningful difference," said Lambert, the OHSU epidemiologist.
Lambert added that the single-year study does not show whether mercury levels change from year to year. He said that is an important question because ocean conditions are undergoing a significant shift, potentially drawing different tuna populations to the West Coast and changing the mix of smaller fish they feed on.
"This is an ongoing process," Lambert said. "The answers are developing, but they are not clear right now."