Mercury levels in tuna have not decreased since 1971, despite emissions reductions

Although environmental policies in recent decades have helped reduce atmospheric mercury emissions from human activities such as coal burning and mining, levels of methylmercury in tuna have not changed since 1971. This is the conclusion of the work, which was published this Wednesday in the journal Environmental Science and Technology Letterswhose authors collected data on total mercury levels from nearly 3,000 tuna samples caught in the Pacific, Atlantic, and Indian oceans between 1971 and 2022.

Methylmercury is a particularly toxic chemical that affects the nervous system, and although its presence in these fish is small, the main health risk comes from cumulative consumption, especially in pregnant women and infants. Researchers set out to determine whether lower concentrations of mercury in the oceans, specifically methylmercury, found in food sources at the top of the food chain, such as tuna, were causing lower atmospheric emissions.

An effect that lingers

What the team of Anna Loren, Anais Media and David Point saw is that mercury concentrations in tuna have been stable over the past 50 years, even though mercury in the air has declined globally over the same period. The latest global agreement, Minimata Convention on Mercury Which took effect in 2017, bans new mercury mines and considers reducing their use, but mercury has already accumulated in the ocean “for centuries,” the article said.

The team believes that static levels in tuna may be caused by “legacy” mercury from deep ocean water being mixed up into the shallow areas where tropical tuna swim and feed. So legacy mercury can be released years or even decades ago and still not show results in reducing air emissions. In addition, these protein-rich fish can accumulate high levels of methylmercury by feeding on contaminated prey, such as small fish or crustaceans, which contribute to the accumulation.

Models predict that even the most restrictive emissions policies would take 10 to 25 years to affect ocean mercury concentrations.

The researchers’ mathematical models simulated three progressively more restrictive environmental policies to support their theory. Models predict that even the most restrictive emissions policies would take 10 to 25 years to affect ocean mercury concentrations, with tuna declining decades later. While the researchers acknowledge that their projections do not account for all the variables in tuna ecology or marine biogeochemistry, the authors say their findings point to the need for a global effort to more aggressively reduce mercury emissions and a commitment to continuous and long-term mercury monitoring. in ocean life.

necessary control

“This is an interesting study that shows that once the sea is polluted, it is not so easy to recover to previous levels,” he says. Joan O. GrimaldiCID-CSIC Research Professor in Applications SMC Spain. “The sea has a large capacity for pollution, so we can use it as a dumping ground without being noticeable a priori. However, precisely because of the large amount of pollutants that it can store, when we want to go back, it is not so simple. ”

“Spain is an important country in Atlantic bluefin tuna aquaculture (Thunnus thynnus), a migratory species, but which is grown on farms and for which biological cycle closure has been achieved in sea cages and terrestrial tanks,” he adds. Diego RomeroProfessor of the Department of Toxicology at the Veterinary Faculty of the University of Murcia, also at SMC. “For this reason, efforts to investigate the importance of mercury in this species are now all the more necessary.”

In any case, specialists remember that the toxic control regulation (RG 1881/2006) regulates the amount of mercury and other heavy metals that can be in food and is analyzed before it goes on the market. That is, there are no fish with a higher value than those indicated on the market, and these values ​​are verified so that there is no health risk due to bioaccumulation.

Source: El Diario

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