Tuna has a lot going for it. It's popular and cheap, loaded with protein and low in fat. And federal health guidelines are simple and direct: We should eat more seafood.
But tuna also is the biggest source of mercury in the American diet.
Mercury is emitted by coal-fired power plants and other industries. It gets into waterways, then into fish, accumulating as it moves up the food chain to top predators such as tuna.
Mercury can harm memory, intelligence, and hand-eye coordination, so federal guidelines advise limited consumption for young children and women who are or may become pregnant. Note: Albacore tuna has more mercury than light tuna.
But the guideline is broad. And a report issued in September by the Mercury Policy Project, a Vermont nonprofit, found that mercury levels in institutional-size cans of tuna, the kind used in schools, vary widely.
The report, "Tuna Surprise," tested 59 samples of institutional tuna from 11 states. The author, environmental health expert Edward Groth, found that children eating the same amount of tuna from different sources could get mercury doses that vary by tenfold. Tuna from Latin America has more mercury than tuna from the United States and Asia.
The good news, to him, is that these days, many schools don't serve tuna. Many kids don't like it.
That's the case in the Philadelphia district, a spokeswoman said.
Plus, she said, tuna isn't as affordable as it once was because it doesn't get subsidies. The U.S. Department of Agriculture must use U.S. suppliers. The major ones have been bought by Asian concerns.
Lower Merion, however, does serve tuna in elementary school - chunk light a few times a week in a salad bar, in two-ounce portions. A spokesman said that even so, tuna is "not a popular choice," and parents haven't complained.
Finkel's own district, Hopewell Valley just outside Princeton, doesn't serve tuna in elementary school. But he was dismayed there was no health-based policy. What if tuna suddenly became cheaper? Or if kids suddenly loved it? Would the district start to serve it regularly?
Finkel considers tuna "a needless risk" and says the smaller the child, the less tuna he or she should eat. Groth's report recommends that children weighing less than 55 pounds eat tuna no more than once a month.
Even in schools where tuna is served sparingly, the problem is the unusual kid who loves it and eats it at every opportunity, Groth and Finkel say.
Meanwhile, an epidemiological study that Groth completed in December, plus eight others, suggest federal guidelines adopted more than a decade ago may not be protective enough.
Because tuna is second only to shrimp in popularity in the United States, how do you decide what to do?
Groth said federal officials were working on an assessment of the risks versus benefits of various seafoods. No word yet.
To Gavin Gibbons, a spokesman for the National Fisheries Institute, suggesting kids should eat less tuna "is nothing short of irresponsible."
Americans already eat the second-lowest percentage of fish in the world, 7 percent, he noted. USDA guidelines say 20 percent of our protein should come from seafood, so "you've got quite a ways to go just to catch up to the benefits."
Last week, first lady Michelle Obama announced the winning recipes in a national "healthy lunchtime challenge." One was from 9-year-old Bence Brown of Omaha, Neb.
The dish? "Terrific Tuna Casserole."
GreenSpace: Tuna and Mercury
Adam Finkel, a Penn expert on human health-risk assessment, recommends parents ask their school district these questions:
How often is tuna served? Worst is if it's on a salad bar every day, so a kid who loves it can load up, Finkel says.
What kind is it? Chunk light has less mercury than albacore.
Where is it from? The "Tuna Surprise" report found that tuna from Latin America has more mercury than tuna from the United States and Asia.
The FDA's information page on mercury and fish: http://alturl.com/fbo2r
The EPA's information page: http://alturl.com/an7wy
"Tuna Surprise" Report: http://alturl.com/m2emc
"GreenSpace," about the environment and health, appears every other week, alternating with Art Carey's "Well Being" column. Contact Sandy Bauers at 215-854-5147, firstname.lastname@example.org, or follow @sbauers on Twitter. Visit her blog at www.inquirer.com/greenspace.