Due to increasing levels of pollution and consumer awareness, numerous studies have been performed to gauge the level of mercury in oceanic fish, including tuna. Mercury is a natural element that can be released into the air through industrial pollution. It can then fall from the air, accumulating in waterways and turning into methylmercury due to contact with the water.
Fish absorb methylmercury and their tissues experience build-up of this potentially dangerous element as they feed in these waters and so it builds up in them. Depending on what the fish eat, their weight, and lifespan, methylmercury builds up more in some types of fish and shellfish than others. For most people, the risk from mercury by eating fish and shellfish is not a health concern. However, a delicate unborn baby or young child’s developing nervous system can be negatively impacted by the high mercury levels in some fish and shellfish. The risks from mercury in fish and shellfish depend on the amount of fish and shellfish eaten and their corresponding levels of mercury.
With respect to tuna, neither the Food and Drug Administration (FDA) nor the Environmental Protection Agency (EPA) advise any individuals, including pregnant women, against eating this type of fish. The four species that these governing bodies warn against for people who are pregnant or mercury wary are: Shark, Swordfish, King Mackerel, or Tilefish. While all types of tuna are deemed to meet or exceed international mercury safety standards, recent studies have shown that mercury levels vary widely by different tuna species. For example, mercury levels are significantly higher in bluefin akami (sushi from lean, dark red tuna) and all bigeye tuna samples than in bluefin toro (sushi from fatty tuna) and yellowfin tuna akami samples. Since mercury is most easily absorbed by muscular, and not fatty tissue, the leanest fish tend to have the highest concentration. Tuna species harvested at more advanced ages also tend to show greater mercury accumulation levels. Moreover, predatory tuna, such as bigeye and bluefin, that eat other mercury-infused tuna tend to bioaccumulate the element, allowing higher levels of the element to permeate their bodies over time due to their toxic diet.
While the fact that fish and shellfish are an important part of a healthy, omega-3 fatty acid rich diet, consumers should be aware of the potential health risks when consuming these products.
While pregnant women and young children are particularly vulnerable, even they are advised by the FDA that they can eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfish that are lower in mercury. If you’re a bluefin or albacore tuna lover, you can still safely eat up to 6 ounces (one average meal) of those species per week.
Tags: Mercury in tuna