The largest source of methylmercury—the most toxic form of the heavy metal mercury—obtained through the diet comes from canned tuna. Thirty-two percent of dietary methylmercury, a known neurotoxin, comes from canned tuna. There are two main types of tuna—albacore and light tuna. Albacore is known to be higher in mercury than light tuna, and so the current federal advisory issued by the FDA and the US Environmental Protection Agency (EPA) recommends that women and young children limit their intake of canned albacore tuna, while recommending consumption of up to 12 ounces of light tuna weekly.

Because canned tuna is inexpensive and nutritious, it is commonly found in the diets of children, who eat twice as much canned tuna as they do any other seafood. The USDA even subsidizes tuna in school lunch programs. A recent study from a group of advocacy organizations in alliance with the Mercury Policy Project set out to test methylmercury levels of canned tuna served in schools.¹ They tested 59 samples of canned tuna from schools in 11 states across the country. The products included six brands of light tuna and two brands of albacore tuna.

The average mercury found in the light tuna was slightly lower than national tests of canned tuna performed regularly by the FDA. The average mercury found in albacore tuna, however, was found to be much higher than the FDA tests—0.560 micrograms per gram compared to the FDA’s 0.350 µg/g. The tests also determined that tuna caught in the United States had the lowest methylmercury levels, especially when compared to tuna from Ecuador, a finding consistent with previous studies that found tuna from Latin America to be particularly high in in methylmercury.²

The report makes a number of recommendations, listed as follows:

• Children should not eat albacore tuna.
• Smaller children (55 pounds or less) should eat light tuna no more than once a month.
• Schools and parents should limit most children’s light tuna consumption to twice a month.
• Schools and parents should identify children who “love tuna” and eat it often, and limit them to two tuna meals per month.
• Children should never be allowed to eat tuna every day.
• Schools, parents, and other caregivers should coordinate their efforts.
• Schools and parents should teach children to enjoy other seafood choices.
• Parents whose children eat tuna once a week or more should have the child’s blood tested for mercury.
• The US Department of Agriculture should phase out subsidies for tuna in the school lunch program.
• The EPA and FDA should expeditiously complete their ongoing effort to revise their joint advisory on seafood consumption and mercury exposure.
• The research and policy communities must urgently address the issue of short-term exposure “spikes.” (This refers to the blood level spikes in methylmercury after eating just one serving of tuna. We simply don’t know if there are long-term adverse effects. More science is needed!)
• Schools should try to avoid buying tuna from Ecuador and other Latin American countries.
• The FDA should meet with other researchers to determine why its reported mercury levels in albacore tuna are substantially lower than what other analysts have found.

Mercury exposure is a major concern when it comes to both children and adults. Brenda has blogged on the topic a number of times. Another recent study published in the journal Environmental Health Perspectives found that children with very high blood levels of methylmercury were more likely to have problems with attention when compared to those with the lowest levels, while those with even mildly elevated blood lead levels (another toxic heavy metal) had greater hyperactivity when compared to those with the lowest levels.³

With ten percent of US children affected by attention deficit hyperactivity disorder (ADHD), according to the CDC, methylmercury in the diets of children should be a major concern. To gain nutrition from fish, opt instead for salmon and sardines, both high in omega-3 fatty acids and low in mercury. Purified fish oil supplements are another excellent way to be sure your children are getting enough beneficial omega-3s.

References

1. E. Groth, “Tuna Surprise: Mercury in School Lunches.” Montpelier, VT: Mercury Policy Project. http://mercurypolicy.org/wp-content/uploads/2012/09/mpp_tuna_surprise_final_final1.pdf
2. K. Malsch and C. Muffett, “Is our tuna ‘family safe’? Mercury in America’s fish.” Washington, DC: Defenders of Wildlife. http://www.defenders.org/resources/publications/programs_and_policy/habitat_conservation/marine/full_report_is_our_tuna_family-safe.pdf
3. O. Boucher, et al., “Prenatal methylmercury, postnatal lead exposure, and evidence of attention deficit hyperactivity disorder among Inuit children in Arctic Québec. Environ Health Perspect. doi:10.1289/ehp.1204976