School Lunch Alert: Too Much Tuna Raises Mercury Worries

For children, a little tuna can add up to a lot of toxicity

Last updated: September 05, 2015 06:00 AM

If tuna sandwiches are your go-to choice for a school lunch, you may be putting your child at risk for ingesting too much mercury, a toxin that can damage the brain and nervous system. And knowing how much tuna is too much is more important than ever, given recent evidence indicating that mercury levels in tuna are on the rise.

Nearly all fish and shellfish have at least trace amounts of methylmercury (the form that accumulates in fish). The highest levels are found in swordfish, shark, king mackerel, and Gulf of Mexico tilefish. But 37 percent of Americans’ dietary mercury exposure actually comes from canned tuna, which ranks second only to shrimp as the most popular seafood in the country.

It doesn’t take too many tuna fish sandwiches to exceed the safety threshold for mercury exposure. For example, a child who weighs less than 60 pounds should not eat more than two ounces of canned albacore (white) tuna per week. That’s less than half the amount of tuna in a typical, five-ounce can. Albacore contains, on average, three times more mercury than the canned light variety, according to Food and Drug Administration (FDA) tests. (See the chart below: "How Much Canned Tuna Can You Safely Eat?")

But even for canned light tuna, the per week safety limit, based on the average mercury level for this variety, for the same under-60-pound child is only five ounces.

The trouble is, the mercury level in canned light tuna can vary wildly. Our analysis found that 20 percent of samples in an FDA study contained almost double the average. And these safety limits are for total exposure, not even accounting for contact with other sources of mercury.

Read our special report on mercury in fish. Also, learn how to reduce your mercury exposure from fish.

It’s not just the tuna brown baggers that have to keep track. Cafeterias often have tuna on the school lunch menu, either in sandwiches or on a salad bar. Odds are the school’s tuna is canned light—the lower mercury kind— rather than albacore. To be sure, ask your school’s food service director. Knowing the type of tuna they serve in school lunch will help you accurately calculate your children’s weekly mercury exposure, using our experts’ chart.

To take it one step further, PTAs and other parent groups may want to work with their schools’ lunch programs to ensure and verify that only the lowest-mercury fish is served. “Recent testing demonstrates significant variations in ‘light’ tuna mercury levels, and new studies also show far greater risks at much lower exposure levels,” says Michael Bender, director of the Mercury Policy Project. The group published a 2012 study, Tuna Surprise: Mercury in School Lunches, which tested mercury levels in samples of canned tuna supplied to school cafeterias. Bender even goes a step further, suggesting that schools avoid tuna altogether.

You can still get the nutritional benefits of seafood with other canned fish, such as salmon, which is higher in healthy fats known as Omega 3 fatty acids than tuna is. "Canned salmon, with its high Omega 3 and lower mercury is a better choice,” says Michael Gochfeld, Ph.D., Professor Emeritus of Environmental and Occupational Medicine at Rutgers Robert Wood Johnson Medical School.

So this year, when you’re packing those lunchboxes, do your kids a favor and try switching out the tuna salad for a salmon salad sandwich instead.

Where do school cafeterias get their tuna?

More than 100,000 schools and residential childcare centers take part in the National School Lunch Program, in which schools receive federal subsidies—cash or food from the U.S. Department of Agriculture (USDA)—for providing free or reduced-price lunches to eligible students. Participating schools are required to serve lunches that meet federal nutrition standards.

Canned light tuna used to be among the foods the program provided, and all of the tuna was purchased from StarKist because it was the only vendor that met USDA rules requiring all foods for the program to be 100 percent U.S. produced. Competing brands lobbied to become eligible providers, but some members of Congress opposed, and the Buy American rule has not changed.

But then the USDA stopped buying tuna for the lunch program in 2012. The impetus? StarKist was cited by the FDA for unsanitary conditions at its processing plant in American Samoa.

According to a USDA representative, StarKist has resolved the issues and is again approved by the USDA to supply tuna for the National School Lunch Program. Even so, the USDA has not resumed purchasing canned tuna for the National School Lunch Program.

“USDA does not currently have plans to purchase canned tuna for the National School Lunch Program, but schools are permitted to purchase tuna directly from private vendors,” the agency representative told us, pointing out that participating schools purchase more than 80 percent of the food for the lunch program, rather than relying solely on the USDA-supplied food.

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