How Worried Should You Be About Mercury in Your Tuna?

Mercury is found throughout the ocean, and is present to some degree in every kind of fish you could choose to consume. It’s both an element found naturally in the environment and a byproduct of manmade pollution. A rule of thumb is that bigger fish tend to have higher mercury levels than smaller ones, because they are higher up in the food chain. The more small fish those big fish eat, the more mercury builds up in their bodies.  

Tuna isn’t the biggest fish in the ocean, of course, but it’s one that is extremely popular and eaten very often by kids and adults of all ages. Canned tuna is the only seafood in some people’s diets. So that’s why mercury contamination is such a concern in this particular fish.

Mercury is a known neurotoxin. Too much of it is harmful to children, whose bodies and brains are still growing. In high amounts it can even be harmful to adults, causing problems with fine motor coordination, speech, sleep, and walking, and prickly sensations. But it’s of particular concern for pregnant people, because the developing brains and nervous systems of their babies are particularly vulnerable to mercury, Rogers says.

In 2017, the Food and Drug Administration issued new, stricter guidelines about which fish are recommended if you are or could become pregnant. Under the FDA guidelines, those vulnerable groups could eat up to 12 ounces (3 servings) of light tuna or 4 ounces (1 serving) of albacore per week, assuming they ate no other fish. (Note that 4 ounces is the amount in a typical 5-ounce can of tuna; the remaining ounce is water or oil.)

In CR’s tests, we looked at 10 products over all, including two varieties from each of the five tuna brands: albacore, which comes from larger tunas and tends to be more expensive; and light tuna (including skipjack), which comes from smaller tunas. CR tested three samples of each product, from different lots, for a total of 30 samples. All the tuna products came packed in water, which was drained before testing. 

While these tests represent a snapshot and are not inclusive of the entire market, they provide insight into what consumers may experience at a moment in time when eating these brands of tuna, and underscore the importance of making safer choices in their daily routines. 

One big takeaway is that albacore has much more mercury than light or skipjack tuna, regardless of the brand. That’s not surprising, since albacore is larger and lives longer than the tunas that make up the light tuna or skipjack tunas. But the disparity was quite wide: The albacore products had three times more mercury, on average, than the others. 

That albacore has more mercury than light tuna is well-known among scientists and seafood experts, but CR’s recent survey found that it may be news to the average consumer. About half of Americans said they did not know that different varieties of canned tuna have different levels of mercury. And 18 percent said that they didn’t know that canned tuna has any mercury at all.

While mercury levels in our test were higher in albacore than in light tunas, some brands had a much larger variation than others. For example, Chicken of the Sea’s albacore had 10 times more mercury than its light tuna, but mercury levels in Wild Planet’s albacore and skipjack tunas were very close to each other. 

None of the albacore tunas in our tests had levels low enough for an adult to have three servings a week and only one, Bumble Bee Albacore, had levels that would allow two weekly servings. The rest of the albacore tunas had levels that warrant just one serving a week, and children shouldn’t have albacore at all.

All but one of the light tunas in our tests had levels low enough that CR’s experts think that, assuming no other fish is consumed, adults who are not pregnant could eat three 4-ounce servings a week, and children could eat two 1- to 4-ounce servings (depending on age). 

The exception: Wild Planet Skipjack Wild Tuna. This light tuna had levels closer to the albacore tunas in our tests, which would allow only one serving a week. (Note that exactly how much tuna you can consume also depends in part on how much you weigh, but CR’s experts believe these guidelines are a good benchmark for everyone to follow to keep track of their mercury consumption.) 

Though mercury levels in light tuna tend to be low on average, it’s clear from CR’s data that there can be unpredictable spikes of the toxin in individual cans. 

Of the 30 samples total, we found six individual spikes in mercury content that would change the FDA’s recommendation about how often someone should eat that particular tuna. That’s 20 percent of the samples, or one in five cans. That’s the same percentage we found when we analyzed the FDA’s data on tuna in 2014. 

Those variations are concerning, Hansen says. “You may know that in general light tuna has less mercury than albacore, but you can’t tell by just looking how much mercury a specific can has,” he says. 

For example, because Wild Planet Skipjack tuna is a light tuna, a consumer may think eating three servings a week is fine. But in our tests, we found two of the three samples of this tuna had mercury levels high enough to put it in the once a week category. And in three samples from the albacore category (two samples of Chicken of the Sea Albacore and one sample of StarKist Selects No Salt Added Albacore), the mercury was high enough that it shouldn’t be eaten at all. 

We reached out to all the companies in our tests and also heard from the National Fisheries Institute (NFI), a trade association that represents canned tuna manufacturers. NFI said that the mercury levels we found were well below the limit that the FDA allows in canned tuna and said these products are safe to consume. StarKist and Chicken of the Sea said their tuna products are monitored for mercury and meet this FDA limit.

Bumble Bee noted that the “health benefits of consuming seafood far outweigh any potential risk, including concerns about mercury.” 

Wild Planet, whose Skipjack Wild Tuna had the highest mercury levels of any light tuna in our tests, said the company “had to make a choice between offering tuna with the very lowest possible mercury level or offering tuna from the best sustainable practice” and that they still have tunas with low mercury levels. 

One of the tuna brands we tested, Safe Catch, notes on its cans that it has the “lowest mercury of any brand.” 

While Safe Catch did have relatively low levels of mercury, we found that most of the other light or skipjack tunas were also low, and the differences in average mercury levels between the Safe Catch cans we tested and those from most other brands were very small. Similarly, the mercury levels in Safe Catch’s albacore tuna was close to most of the albacore samples from other brands we tested and one brand, Bumble Bee, actually had lower levels. Safe Catch’s Wild Albacore tuna costs up to about $5 a can and its Wild Elite light tuna up to about $3.50, compared to less than $2 for light tuna and less than $3 for albacore from Bumble Bee, Chicken of the Sea, and StarKist. (Wild Planet’s skipjack and albacore costs up to about $3.50 and $5.60, respectively.)

Bryan Boches, CEO and founder of Safe Catch, told CR that the company has “tested over 6 million individual tuna so we know that mercury varies widely in tuna regardless of catch method, size or location” and that it is “the only brand that tests each individual tuna to a strict mercury limit before it is accepted.” No other brand in our test claims to test every tuna.

While the risk of mercury in tuna has been known for years, CR’s recent spot check is a reminder that the problem is far from solved. And though mercury in the oceans can be naturally occurring, experts emphasize that human pollution, notably the burning of fossil fuels, remains a major cause of pollution of the atmosphere, and eventually the oceans. 

Experts who study mercury contamination in fish have found that levels of it in different oceans appear to be linked to different practices and policies in the nations nearby. For instance, mercury contamination in tuna caught in the Pacific Ocean is on the rise, but levels are dropping in tuna from the Atlantic Ocean, says Nicholas Fisher, PhD, a distinguished professor in the School of Marine and Atmospheric Sciences at the State University of New York at Stony Brook. ​​

"In China and India, they burn a lot of coal for electricity, and when you burn coal, you release a lot of mercury into the air, which eventually rains down; so mercury levels have been increasing somewhat in the Pacific,” Fisher says. “Whereas in the Atlantic, we’ve shown that the levels have declined a little bit, primarily because of efforts made in North America...to sort of scrub the mercury from coal-fired plants in the U.S. and Canada.” 

This disparity in mercury pollution in different parts of the world suggests a possible solution, says Elsie Sunderland, the Gordon McKay Professor of Environmental Chemistry at Harvard University. The more we reduce mercury emissions into the atmosphere, the more we can reduce mercury contamination in the oceans, and we are seeing the effects of policy changes already. 

Sunderland and her colleagues have estimated that U.S. power plants have reduced their mercury emissions by 90 percent from 2008 to 2020, which they attribute to stricter regulations from the EPA. The U.S. has also made strides in removing mercury from the manufacturing of all types of consumer products—not just old-fashioned mercury thermometers, but also batteries, electric components, paints, pesticides, and more. 

CR’s own tuna testing inspires some optimism as well. The mercury levels that CR measured in four out of five of the brands in our recent test were actually lower than the average mercury levels the FDA measured from 1990 to 2010. 

“People feel depressed about these issues, and worried that our actions aren’t making any changes,” Sunderland says. But “if you look at the situation in the United States, actually we’ve done a huge amount and been incredibly successful. So I do feel like that model could be followed, globally.”