A Breakthrough in Seafood Safety

In a groundbreaking study, researchers from top institutions including the ESRF, CNRS, ENS Lyon, and Norway's Institute of Marine Research have illuminated how Atlantic Bluefin tuna navigate the perils of mercury toxicity. Published in Environmental Science & Technology, their findings reveal that while these majestic fish contain toxic methylmercury, they also possess mercury bound in stable, non-toxic compounds within their edible muscle.

Mercury: A Global Health Menace

Mercury contamination is a significant concern for seafood lovers worldwide. This harmful element originates from both natural phenomena like volcanoes and forest fires, as well as man-made sources including coal burning and industrial waste. Bacteria convert mercury into methylmercury, which then bioaccumulates in the food chain, posing risks, especially to apex predators like tuna.

A New Perspective on Mercury Measurement

Alain Manceau, the leading researcher of the study, emphasizes that understanding mercury's toxicity means looking beyond total mercury measurements. He advocates for testing specifically for methylmercury: "We need to refine our testing methods to focus on this toxic form rather than just total mercury, which can mislead consumers about the actual risk," he states.

How Bluefin Tuna Detoxify Methylmercury

Using the high-energy X-ray beams at ESRF, researchers investigated how Atlantic Bluefin tuna process mercury. Unlike other marine predators, these tuna rely heavily on their spleen for detoxification. The interaction of selenium, an essential nutrient in seawater, with mercury is key. This relationship forms less harmful mercury–selenium complexes, showcasing the intricate ways these fish mitigate toxicity.

Unique Insights from Powerful Science

Utilizing advanced synchrotron techniques, the research team discovered that some mercury in Bluefin tuna’s muscle exists as a non-toxic tetraselenolate complex. This complex transforms into inert mercury selenide in the spleen, revealing that not all mercury is created equally.

Different Tunas, Different Risks

The study focused on large Atlantic Bluefin tuna, which can weigh up to an astonishing 300 kg. However, as high-trophic predators, the findings here cannot be generalized to other, lower-trophic tuna species like albacore or skipjack, which tend to have lower mercury levels.

Implications for Seafood Consumption

This research underscores the importance of distinguishing between toxic methylmercury and benign mercury–selenium complexes in seafood testing. Manceau concludes, "Up to 25% of the mercury in Bluefin tuna may be in less harmful forms, highlighting that the health risks are dependent not just on the quantity of mercury, but significantly on its chemical makeup." This provides a fresh perspective for consumers seeking safer seafood choices.