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Mercury levels in tuna unchanged since 1971

By Dennis Thompson, HealthDay News
Their analysis of nearly 3,000 tuna samples caught in the Pacific, Atlantic and Indian Oceans between 1971 and 2022 revealed stable mercury concentrations in tuna during those five decades. Photo by Adobe Stock/HealthDay News
Their analysis of nearly 3,000 tuna samples caught in the Pacific, Atlantic and Indian Oceans between 1971 and 2022 revealed stable mercury concentrations in tuna during those five decades. Photo by Adobe Stock/HealthDay News

Mercury levels in tuna haven't changed since 1971, despite efforts to reduce emissions of the toxic metal into the environment, researchers report.

Their analysis of nearly 3,000 tuna samples caught in the Pacific, Atlantic and Indian Oceans between 1971 and 2022 revealed stable mercury concentrations in tuna during those five decades.

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The research team specifically looked at the tropical tuna species of skipjack, bigeye and yellowfin, which account for 94% of global tuna catches.

Environmental policies have helped reduce mercury pollution from human activities like burning coal and mining, researchers said.

Over the same five-decade period, airborne mercury pollution decreased globally, researchers noted.

The unchanging mercury levels in tuna might be caused by "legacy" mercury rising up from deeper regions of ocean water, mixing in with the shallower depths where tropical tuna swim and feed.

This legacy mercury could have been emitted years or even decades earlier, so it wouldn't reflect efforts to clear airborne mercury emissions, speculated the research team led by marine ecologist Anne Lorrain, director of research at IRD Quest in France.

Methylmercury is a particularly toxic chemical that affects the nervous system, and is the primary form of mercury in tuna contamination, researchers said. Unborn babies and young children are at highest risk of harm from exposure.

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The mathematical models used by the researchers tested three progressively more restrictive environmental policies that might lower mercury levels in tuna.

The models predict that even the most restrictive measures would take 10 to 25 years to influence ocean mercury levels, and that drops of the levels in tuna would follow decades later.

The researchers argue their findings point to the need for a worldwide effort to tackle mercury emissions more aggressively, as well as continue to monitor mercury levels in marine life.

The new study was published Wednesday in the journal Environmental Science & Technology Letters.

More information

Consumer Reports has more about mercury in tuna.

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