What’s the difference between canned albacore “white” tuna and canned “light” tuna? Their mercury levels, according to a recent fish advisory by federal agencies.
Last week, the United States Food and Drug Administration (FDA) and Environmental Protection Agency (EPA) for the first time gave joint advice on what types of fish are best to eat for those concerned about toxicity from mercury. Because that metal pollutant is harmful to the developing brain, health officials suggest that pregnant women, nursing mothers, women who may become pregnant, and young children reduce their intake of mercury.
FDA and EPA recommend that adults in those groups eat no more than 12 ounces per week of a variety of fishes and shellfish that are low in mercury. These include shrimp, salmon, pollock, and catfish, as well as fish sticks and fast-food fish sandwiches. For young children, a smaller amount is recommended.
The officials advised similar limits on canned light tuna. However, they recommend only 6 ounces—that is, one average meal—of canned albacore tuna. That distinction is based on the most recent results of an FDA study that shows that the canned albacore variety has more mercury than canned light tuna does. On average, canned albacore contained mercury at 0.35 parts per million, while light tuna had 0.12 ppm.
Canned tuna is one of the most heavily consumed finned fish in the United States, says David McBride, a toxicologist from the Washington State Department of Health. Therefore, it’s a primary source of mercury for most people.
According to a 2000 National Research Council report, studies have shown that pregnant women who showed high concentrations of mercury in their blood were more likely than usual to give birth to children with various disabilities, including mental retardation and cerebral palsy. Exposure of children before birth to smaller amounts of mercury has been linked with poor performance on neurobehavioral tests. A study in the April, 2003 Journal of the American Medical Association estimated that 8 percent of U.S. women had blood mercury concentrations exceeding levels that EPA considered safe.
A person’s body naturally removes mercury from the bloodstream at a slow rate. The mercury concentration drops by half every 70 to 90 days McBride says.
Before the new advisory, information on mercury concentrations in canned tuna was insufficient, says McBride. As more knowledge emerged on the adverse health effects of mercury, people wanted to find out whether they should change their patterns of food consumption. Moreover, McBride says, “many states, I think, felt that the FDA [which normally gives consumer advice on commercially caught fish] wasn’t giving the word out on canned tuna, so they issued their own fish advisories for canned tuna.”
The recommendation from EPA and FDA is the first national statement on mercury concentrations in canned tuna. McBride says that the recommendations complement his team’s recent work.
Last year, McBride and his colleagues independently examined canned tuna. They measured mercury concentrations in the contents of 130 cans of white tuna and 159 cans of light tuna. Their results were similar to those from FDA’s study; mercury levels in white tuna were higher—by about 0.15 ppm—than in light tuna. This difference appeared regardless of whether the tuna had been packed in oil or water and whether it was chunky or solid. The researchers presented their results in San Diego at the National Forum on Contaminants in Fish last January.
McBride explains that canned albacore tuna has more mercury than light tuna has because the albacore are larger and longer-lived than the skipjack species that often make up canned light tuna.
Interestingly, the mercury concentrations that McBride’s team reported are only about half as high as those that FDA found. McBride says he doesn’t know how to explain the difference because both studies examined the same major brands of tuna.
Compared to canned light tuna, tuna steaks tend to come from older, larger, and, therefore, more contaminated fish. So, the advisory suggests no more than 6 ounces of tuna steaks per week for women of childbearing age and children.
This group should avoid mercury-loaded shark, swordfish, king mackerel, and tilefish, the advisory urges.
Taking advantage of “better scientific information and various public health and safety initiatives . . . Americans can and should feel comfortable consuming fish,” says FDA deputy director Lester M. Crawford. In the current advisory, he says, “we are outlining a clear set of guidelines to help Americans continue to consume and enjoy the health benefits of fish while lowering the risk of any harmful effects of mercury.”