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  • Writer's pictureOindrila Ghosh

How much Tuna is a safe dietary choice?

Updated: Aug 16, 2023

- Oindrila Ghosh, Jada Damond

Over the period of my graduate studies, I developed a liking for environmental modeling of contaminants. However, spending all my time on the computer, I have developed a Vitamin D deficiency from the lack of sunlight – a very common phenomenon for people these days due to our sedentary lifestyles. My doctor noted that not only is seafood a great source of Vitamin D, it is a heart-healthy food also rich in omega 3 fatty acids and riboflavin, among other nutritional benefits. So, I started to incorporate tuna in my diet. I perfected a tuna salad sandwich, which my husband and I enjoy for breakfast – the two of us share one 5-oz can of light tuna over at least two days.

It came as a shock to read this recent Consumer Reports (CR) article which states that about 20% of the 30 tested tuna cans across several brands had mercury (Hg) spikes over their reported average, although they did not go into the details of the actual concentration levels. CR say that these spikes would change the FDA's recommended consumption limit. Fish is well-known for posing a risk of Hg poisoning to consumers. When Hg pollutes body of water, it is microbially transformed into methylmercury and subsequently taken up by aquatic wildlife. Methylmercury is very bioaccumulative; levels in certain fish increase going up the food chain, as predatory fish eat contaminated prey. Consequently, prolonged heavy fish consumption can lead to adverse neurotoxic and neurodevelopmental effects (among others), particularly posing a risk to developing fetuses, breast-fed babies, and young children. This risk was a reality for this victim, who discovered his loss of balance, numbness in his lips, and tingling in his feet were attributed to Hg poisoning after increasing his fish consumption in attempt to adopt a healthier diet.

The CR article raises an important question: “Is Tuna a good dietary preference? If yes, how much is the safe limit of consuming it?” The type of fish consumed certainly determines one’s risk of Hg poisoning. For example, the larger (and more expensive) Albacore tuna was reported to have almost three times more Hg levels than the smaller light tuna (including skipjack). The Food and Drug Administration (FDA) posted fish consumption guidelines which recommend how much of certain types of fish consumers should stick to and what fish to avoid. These guidelines are based on a reference dose (RfD) reported by the Environmental Protection Agency (EPA) above which adverse effects can occur – specifically, neurotoxic effects in babies and young children exposed in utero or by their oral consumption. The EPA RfD, which incorporates a 10-fold uncertainty factor for pharmacokinetic and pharmacodynamic variability, is 0.1 µg methylmercury per kilogram of human body weight per day. From this RfD, the FDA calculated the safe amount of fish to be consumed, based on average Hg levels in several types of fish. Considering the serving size for adults as 4 oz (113 grams) the FDA recommends at most one serving of albacore tuna and two servings of light tuna per week. This informs me that I should not eat more than 8 light tuna or 4 albacore tuna sandwiches (from de-watered tuna cans) per week.

Risk assessment is a well-known concept among environmental scientists and engineers defined by the EPA as the process of ‘characterizing the nature and quantifying the magnitude of health risks to humans and ecological receptors from chemical contaminants and other stressors that may be present in the environment.’ Risk communication is the real-time exchange of this information of the potential risk between experts and public, in the form of advice and opinions. Thus, risk communicators are an essential link between the scientific world and the people exposed to the imminent threat from the stressors in the environment. Any form of ambiguity in the language from the risk communicators at the supply end of products can make it difficult for consumers to take the right decision. Taking this deep dive raised another important question about communication to consumers, “Are we, as consumers, getting the true picture of the risk associated with having chosen can of tuna?”

The EPA RfD and FDA consumption guidelines are based off average measured Hg levels in fish, which can vary from site to site and even fish to fish, leading to the Hg level spikes observed by CR. Many tuna companies do not test every fish they sell, which in their defense is an expensive endeavor. It is up to the consumer to be informed about the risks of their fish consumption. However, although EPA’s RfD (and subsequently FDA’s fish consumption guidelines) are partially based on exposure to fetuses in utero, because of the variability observed across tuna cans, CR also recommends that pregnant women avoid canned tuna altogether.


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