Tuna is one of the most popular seafood worldwide. But these protein-rich fish can produce high levels of methylmercury by feeding on contaminated prey such as small fish or crustaceans. Despite efforts to reduce mercury emissions into the environment, researchers report in the ACS. Environmental Science and Technology Letters that tuna levels appear unchanged since 1971; They warn that more aggressive emission reduction targets are needed to lower tuna mercury levels.

Environmental protection policies have helped reduce mercury pollution from human activities such as coal burning and mining around the world. However, people can still be exposed to methylmercury, and infants and young children are most at risk of harm. Methylmercury is a particularly toxic chemical that affects the nervous system and is expected to be the primary form of mercury in tuna contamination. So, the researchers set out to determine whether lower air emissions resulted in lower concentrations of mercury in the oceans, specifically methylmercury found in food sources that are at the top of the food chain, like tuna. I sit. Anne Lorrain, Anaïs Médieu and David Point worked with an international team of researchers to investigate mercury trends in tuna over the past 50 years. They also wanted to simulate the effects of different environmental policies on future marine and tuna mercury levels.

The researchers compiled their own data and previously published data on mercury levels from nearly 3,000 tuna muscle samples from fish caught in the Pacific, Atlantic and Indian Oceans from 1971 to 2022. These three species account for 94% of global tuna catches. Because they do not undergo a transoceanic migration, any contamination found in the animals’ muscles likely reflects the water in which they swim.

After standardizing the data to allow comparisons across decades and regions, the researchers observed stable tuna mercury concentrations worldwide from 1971 to 2022, except for an increase in the Pacific Northwest in the late 1990s. However, airborne mercury decreased globally during the same period. The team theorized that the “inheritance” in tuna may be due to upward mixing of mercury at depths below static sea level water depths where tropical tuna swim and feed. Legacy mercury could have been released years or even decades ago and still not show the effects of reduced emissions in the air.

The researchers’ mathematical models that simulate three progressively more restrictive environmental policies support their theory. Models predict that it would take 10 to 25 years for even the most restrictive emissions policy to affect ocean mercury concentrations, and then decades later for tuna to decline. Although the researchers acknowledge that their predictions don’t take into account all the variables in tuna ecology or marine biogeochemistry, they stress their findings need to more aggressively reduce mercury emissions worldwide. And a commitment to long-term and continuous monitoring of mercury in marine life is needed. .

The authors acknowledge funding from the French National Agency for Research, the University of Western Brittany and support from the Integrated Marine Biosphere Research Regional Program under the International Framework for Climate Impacts on Oceanic Top Predators.