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Canned Tuna May Contain Excessive Mercury

The tunafish often served in school lunches may contain too much mercury, according to environmentalists' testing
tuna sandwich



flickr/Dave Lifson

Canned albacore tuna purchased by U.S. schools contains more mercury than what government officials have reported, raising the risks for some tuna-loving kids, according to a new study from a coalition of advocacy groups.

Children who eat two medium servings of albacore, or white, tuna per week could be exposed to as much as six times the dose that federal guidelines consider safe, according to the report prepared for the Mercury Policy Project. It is the first study to test the mercury content of tuna brands purchased by schools.

The report recommends that all children avoid eating albacore tuna. In addition, it advises children under 55 pounds to limit “light” tuna to one meal once a month, and twice a month for children over that weight.

Since 2004, the U.S. Food and Drug Administration and Environmental Protection Agency have recommended that pregnant and nursing women, women who may become pregnant and young children limit canned white tuna to six ounces per week. Light tuna – made from a species known as skipjack ­– contains less mercury so the government recommends no more than 12 ounces per week.

But the advocates say those recommendations are too lax because their tests show that "customers who choose canned albacore tuna may fairly frequently get mercury levels more than twice the FDA's average for the species," the report says.

Light tuna, on the other hand, was slightly lower in mercury than FDA tests have shown.

FDA officials and representatives of tuna companies were unavailable for comment on the findings.

Mercury is a neurotoxin that builds up in fish, particularly larger ones such as albacore tuna.

Because canned tuna is a cheap, nutritional food that is popular in schools, parents should rotate other fish into their children’s diet to reduce their risk of neurological effects, the report suggests.

“Most kids don’t eat that much tuna, so nothing really is needed to modify the behavior of a majority of kids,” said Ned Groth, co-author of the report and former senior scientist at the Consumers Union. “Kids who are probably above the ninetieth percentile in terms of how much tuna they eat, that’s where I’d focus my attention.”

Scientists not involved with the study generally agreed with the report’s advice.

“They are probably good, conservative recommendations,” said University of South Carolina assistant professor Jennifer Nyland, who studies mercury’s effects on autoimmune diseases.

A panel of scientists from the National Research Council concluded more than a decade ago that prenatal exposure to mercury reduces the mental abilities of children, including their motor skills, attention and IQs. The FDA and EPA fish consumption guidelines are based on 25 years of studies of effects in Faroe Islands children highly exposed to mercury in the womb.

There is little data, however, on the health risks for children, rather than their pregnant mothers, who eat tuna. Industry groups argue that kids have been eating tuna fish sandwiches for years with no apparent harm.

“Nobody can really say what the effects on children are, because nobody has really looked,” Groth said. “It’s perfectly reasonable to assume that a child is vulnerable to methylmercury poisoning, although there’s no epidemiological evidence right now.”

The groups’ recommendations for limiting kids’ consumption of light tuna are much more restrictive than any experts have recommended. Their goal was to keep kids’ mercury exposures within 25 percent of the EPA’s recommended “safe” dose, even though the EPA already has built a 10-fold margin of safety into that dose. Groth said that is a valid goal given the scientific uncertainty about the risks to children.

The levels of mercury in 11 samples of albacore canned tuna averaged 0.560 micrograms of mercury per gram of tuna. The average reported by FDA this year is 0.350 micrograms per gram. The sample size is small, but three out of the 11 cans had mercury levels more than twice the average values reported by the FDA.

The average mercury level in 48 samples of “light” tuna was roughly one-third the amount found in the white tuna.

The report adds to other research showing that albacore has more mercury than FDA tests have revealed.

“The main value of this study is that it points out that because tuna, especially white, or albacore, can be moderate-to-high in mercury ­– and because canned tuna is so popular in our diets – that mercury exposure from canned tuna is of concern,” said Roxanne Karimi, a marine scientist at Stony Brook University who was not involved with the study. Karimi’s research also has shown that mercury levels in fish vary widely from what the FDA reports.

The new study examined the mercury concentrations in 35 large (66.5 oz) cans and 24 large (43 oz) foil pouches from brand lines and products sold specifically to schools. The tuna was from six brands of “light” tuna and two brands of albacore tuna, including Sunkist and Chicken of the Sea, which made up 60 percent of the light tuna studied.

Fifty of the 59 tuna samples were imported to the United States. The nine samples of U.S.-caught tuna had the lowest average mercury concentration. “Light” tuna from Ecuador had the highest. 

In the study, tuna mercury levels were highly variable between samples, which means parents or schools can’t easily judge its safety, Groth said. The report suggests that schools should avoid buying tuna from Ecuador and other Latin American countries, instead buying U.S. or Asian tuna.

Groth said the take-home message for parents isn’t that their kids should stop eating fish. “Focus on kids who eat too much tuna and give them other kinds of nutritious seafood,” he said. “Don’t stop eating tuna. It’s OK for most kids.”

The report was co-sponsored by nine other advocacy groups, including Physicians for Social Responsibility and the Center for Science in the Public Interest.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.

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