|See this related seafood lobby fable:|
|Fable: Canned light tuna is a “low-mercury” fish|
Americans now eat more shrimp than any other seafood item (see Top 10 list), but tuna is the most popular fish we consume. One out of every six of our seafood meals is tuna, and most of it is canned tuna. Of the two popular varieties, about three times as much canned light tuna (the less expensive variety) is consumed as canned albacore (or “white”) tuna. Fresh and frozen tuna steaks and tuna sushi are also popular choices, although they make up much smaller fractions of the market. Canned tuna, especially the canned light variety, is an inexpensive source of high-quality protein. Although sales have been declining as Americans have responded to a growing variety of seafood choices, canned tuna is still very popular. It’s a favorite sandwich ingredient for families with children, and a staple of the Federal school lunch program.
Unfortunately, as long-lived ocean predators, tuna accumulate methylmercury. Shrimp has the lowest methylmercury level among seafood items, with 0.012 part per million. In contrast, canned light tuna contains 10 times as much mercury, 0.118 part per million. Canned albacore tuna and fresh/frozen tuna steaks contain 0.353 and 0.384 part per million mercury, respectively, about three times as much as canned light has. Tuna sushi, often made from large bluefin tuna, which are older and therefore have higher mercury levels, contains about 1.0 part per million mercury, putting it on a par with swordfish and shark among the highest-mercury fish.
Because of its popularity and because all varieties of tuna have relatively high mercury levels, tuna is by far the largest source of methylmercury exposure in the American diet. In an analysis submitted to the FDA in April 2009, The Mercury Policy Project showed, using FDA’s own data, that tuna accounts for 37.4 percent of all the mercury in the US seafood supply. (See page 19 of the linked document.) By comparison, the four highest-mercury varieties combined, swordfish, shark, king mackerel and Gulf tilefish, account for just 6.5 percent of total mercury contributions. In other words, tuna is responsible for six times as much mercury exposure as the four very-high-mercury fish varieties the government advises pregnant women not to eat.
People who would like to minimize their methylmercury exposure therefore need to be aware of the central role played by tuna fish in that exposure. Achieving that awareness has not been as easy as it should be. Advertisements from the tuna industry have urged people, including pregnant women, to eat more tuna, and to ignore mercury concerns. And the government has been less than helpful. The 2004 EPA/FDA advisory urges women to limit their consumption of canned albacore tuna, but inaccurately lists canned light tuna as a “low-mercury” seafood choice, and recommends eating up to 12 ounces of it per week.
Fable: Canned light tuna is a “low-mercury” fish.
Facts: This particular nugget of misinformation originated with the US FDA, although the tuna lobby has been more than happy to propagate and benefit from it.
The truth is, while canned light tuna has only one-third as much mercury as canned albacore tuna, it still has a well-above-average mercury content. The average mercury level in the US seafood supply as a whole, calculated by FDA (and confirmed by our own independent analysis) is 0.086 part per million. The average level in canned light tuna, 0.118 part per million, is 37 percent higher than the overall average. Given its very large market share and this elevated mercury content, canned light tuna is the biggest single source of methylmercury exposure in the American diet, accounting for 16 percent of the mercury in the seafood supply.
Further, not all canned light tuna is the same. The FDA average figure of 0.118 part per million is based on extensive sampling of major US brands of tuna—Bumblebee, Star-Kist and Chicken of the Sea. But FDA has not done much testing of “minor” tuna brands, including brands imported from South and Central America. Some of the latter brands have average mercury levels much higher than the average in US brands. Also, amounts of mercury in individual cans of even the major US brands vary, and some cans have much higher than average levels. Because of this variability and uncertainties about the timing of potentially harmful exposure during fetal development (see “The Reference Dose is for Lifetime Exposure“), several consumer and public-health organizations have advised pregnant women to avoid all tuna, including canned light. We think that’s sound advice.
Why, then, would the FDA advise pregnant women to eat up to 12 ounces of canned light tuna per week? One reason is that FDA scientists simply were not very concerned about the risks of low-level methylmercury exposure. Also, when it was developing the 2004 advisory, FDA was in a difficult political position. Its draft Advisory, circulated for public and interested-party comments, urged women to limit their consumption of canned albacore tuna. The tuna industry had commented pointedly on the draft, stressing its concern that if the advisory said anything negative about mercury in tuna, it could have a substantial adverse impact on the billion-dollar annual market for canned tuna.
Consumer organizations, in comments on the draft Advisory, had urged FDA not merely to warn consumers about high-mercury fish, but also to identify low-mercury choices. FDA then had to determine what should be considered “low-mercury.” Where should it draw the line? As our table of mercury levels in fish shows, 0.050 parts per million might have been a sensible place to draw that line: Seven of the 11 top-selling fish and shellfish varieties and 15 types of fish and shellfish overall, have 0.050 part per million mercury or less. In all, 25 fish and shellfish categories (some of which, like crabs, clams and flatfish, contain many separate individual seafood varieties) have lower average mercury levels than light tuna. Why, then, would FDA choose to define “low-mercury” so it included canned light tuna, the largest source of methylmercury exposure in the diet?
At the FDA Food Advisory Committee meeting on December 10, 2003, FDA scientist Clark Carrington explained: “In order to keep the market share at a reasonable level, we felt we had to keep light tuna in the low-mercury group.” (See the transcript of the meeting, Carrington’s comments on pages 162-163.) So there you have it: FDA defined the so-called “low mercury” category specifically to include canned light tuna, not to help women minimize their exposure to methylmercury, and not because canned light tuna actually is low in mercury, but to protect the tuna industry’s market from the impacts it might have felt if FDA had explained truthfully that light tuna is Americans’ largest single source of methylmercury exposure.
Needless to say, we don’t believe the economic interests of the tuna industry should override the need for accurate public-health advisories about sources of mercury in the diet. Unless and until FDA corrects this error, however, the industry will benefit—and consumers will endure easily avoidable mercury exposure—because of the fable that light tuna is a “low-mercury” choice.