Why does tuna contain a lot of mercury?

Tuna is an outstanding source of nutrients providing high quality protein, fatty acids that are good for the heart and brain, along with essential vitamins and minerals such as vitamin D, B12, and selenium. However, this nutrient-rich fish has a major limitation: it is full of mercury, a heavy metal that is harmful to the nerves, according to IFL Science.

Compared to most other seafood, tuna meat has relatively high levels of mercury. The US Food and Drug Administration (FDA) estimates that tuna contains an average of 0.126 and 0.689 parts per million of mercury. Some types of tuna have even higher concentrations. For example, albacore tuna, also known as albacore tuna, typically contains about 3 times more mercury than skipjack or yellowfin tuna.

Most fish with high concentrations of mercury are apex predators such as sharks, swordfish, sailfish, and king mackerel. This is due to bioaccumulation. Inorganic mercury enters the natural environment through industrial pollution, then is converted to its organic form, methylmercury, by microorganisms in marine ecosystems. Small amounts of methylmercury can also form naturally by bacteria in water and sediment.

This chemical is consumed by small aquatic organisms, which in turn become food for larger predators in the food chain. Because mercury is absorbed faster than it is metabolized or excreted, large amounts of the metal accumulate at each level of the food chain, with apex predators consuming the most. Mercury is so abundant in the environment that even tuna living in the middle of the ocean contains some amount of this chemical.

A 2024 study found that mercury levels in tuna have remained unchanged despite a decline in global mercury emissions since the 1970s. Researchers speculate that the steady mercury levels in tuna may be due to results from the upward movement of mercury from deeper ocean layers to surface waters, where tropical tuna often feed. Most likely it was mercury released into the environment years or decades ago.

The amount of mercury in food is very small but can gradually accumulate, especially if consumed in large quantities over a long period of time. According to the Environmental Protection Agency (EPA), symptoms of methylmercury poisoning can include problems with peripheral vision, a stinging sensation, often in the hands, feet and around the mouth, lack of coordination, The ability to talk, hear and walk is affected, muscles are weakened.

However, you need to consume fairly large amounts of tuna over a long period of time before you need to worry about mercury poisoning. Some scientists estimate that healthy adults can consume about 95 grams of tuna a week before risking serious mercury poisoning.