Mercury Levels in Tuna Are the Same Since 1971

Scientists say mercury levels in fish have remained constant despite a global decline in polluting industries. For people who eat fish like tuna, this suggests that the risks of mercury exposure have also remained the same.

While fish and seafood are high in nutrients critical for human health, such as omega-3s, iron, and iodine, they can also contain mercury — a naturally occurring yet toxic element.

For those trying to adhere to a diet rich in seafood, such as the Mediterranean diet, the thought of eating fish like tuna is often sidelined by concern over potential exposure to this harmful toxin.

Mercury enters the ocean via industrial sources, land runoff, and atmospheric deposits. Microbes in ocean waters convert mercury to methylmercury, which is consumed by plankton and other sea life. Small fish eat these sea creatures, which are then consumed by larger fish. As mercury moves through the food chain, it becomes more concentrated. That's why larger fish species like tuna have higher levels of mercury.

Mercury emissions from manufacturing are lower than they were decades ago, but it's unclear if this reduction has impacted mercury levels in fish.

According to the U.S. Food and Drug Administration (FDA), methylmercury in fish can negatively affect all people, regardless of age or health status. However, unborn babies, infants, and children are particularly at risk for adverse health effects from mercury exposure. These effects include memory and cognition issues, lower intelligence quotients (IQ), and motor skill delays.

Mercury levels in tuna remain stagnant

New research has revealed that mercury in tuna remains the same amount as it did over 50 years ago. The new data is disappointing to scientists and environmentalists as they had hoped the reduction of polluting industries like mining would have lowered mercury levels in seafood.

To conduct the study, published in Environmental Science & Technology Letters, scientists gathered previous and current data on total mercury levels from nearly 3,000 tuna caught in the Pacific, Atlantic, and Indian Oceans between 1971 and 2022. The team looked at skipjack, bigeye, and yellowfin — three species that account for most of the global tuna harvest.

After analyzing the data, the scientists found that from 1971 to 2022, mercury concentrations in tuna remained stable worldwide, except for increased levels among tuna samples from the northwestern Pacific Ocean in the late 1990s.

The team believes this flatline effect is likely due to the inactivity of surface ocean mercury that has accumulated over centuries.

"To achieve measurable declines in mercury concentrations in highly consumed pelagic fish in the near future, aggressive emission reductions and long-term and continuous mercury monitoring in marine biota are needed," the study's authors wrote.

Still, the data could be considered reassuring in some respects, as it shows mercury concentrations in tuna are not getting worse. This is a rarity in today's world, where reports suggest the levels of other contaminants such as PFAS or forever chemicals and microplastics are skyrocketing.

How much tuna should a person eat?

Though mercury in fish has remained unchanged for over 50 years, it's still present at high levels in certain species.

The FDA says that since fish provide vital nutrients, it should be part of a healthy eating plan for people of all ages, including pregnant individuals.

The FDA and the Environmental Protection Agency (EPA) recommend that adults, including pregnant individuals, should consume about 8 to 12 ounces of fish per week, and children should eat two servings of fish each week. They suggest that people choose fish low in mercury, as the FDA/EPA's Advice About Eating Fish Chart indicates.

Advice About Eating Fish Chart
Image courtesy of the FDA and EPA

While the chart shows bigeye tuna has the highest mercury levels and should be avoided, other species, like canned skipjack, are likely safer choices. Because they contain slightly higher mercury levels, fresh, frozen, or canned tuna such as albacore and yellowfin are considered good choices as long as they are consumed in moderation.

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