Scientists Discover a Simple Method to Reduce Mercury Levels in Tuna

The benefits of getting fish in your diet are well known (it's in the Mediterranean diet, for example), but mercury poisoning remains a concern. Now, scientists have figured out how to cut levels of mercury in fish by up to 35 percent with a tweak to how it's packaged.

A team from the Swedish University of Agricultural Sciences and Chalmers University of Technology experimented with adding the amino acid cysteine to canned tuna – one of the types that can have the most mercury in it.

When tuna is immersed in water containing cysteine, the novel solution removed 25 to 35 percent of the mercury from the fish, according to lab tests. The more fish flesh that was in contact with the solution, the more mercury was taken out into the liquid.

Cysteine was picked for the solution because of the way mercury strongly binds to it – which is how it's able to build up in fish in the first place – and following on from a previous study into mercury removal by the same researchers.

"We believed this would allow some of the mercury to be drawn out and instead bind to the solution and be discarded," says chemist Przemysław Strachowski, from Chalmers University of Technology. "Further research is needed to take care of the removed mercury."

If you've been eating fish without any knowledge of any potential mercury contamination, don't worry: you're unlikely to be consuming enough of it for there to be a danger, though it's recommended that pregnant women and young children only eat a limited amount.

In most cases, the health benefits of eating fish outweigh the potential health risks – though finding a way to reduce mercury levels in fish through the way the food is packaged would certainly reduce those risks even further.

"The beauty of this type of packaging is that it is active while the product is on the shelf," says Strachowski. "No additional production steps would be needed if a method like this were used industrially."

"The application of our results could increase the safety margin for fish consumption."

There were no noticeable changes in the appearance or smell of the fish samples treated with cysteine in the study, and mercury removal continued for up to two weeks. No extra additives were required for the solution to work.

It's going to take further research to turn this into a practical option for fish storage, but the early signs are promising – and the team thinks the methods outlined could be improved in the future.

"Our study shows that there are alternative approaches to addressing mercury contamination in tuna, rather than just limiting consumption," says food scientist Mehdi Abdollahi, from Chalmers University of Technology.

"Our goal is to improve food safety and contribute to enhanced human health, as well as to better utilize food that is currently under certain restrictions."

The research has been published in Global Challenges.