Tuna the Wonderfish is the newest marketing movement sponsored by the 3 largest tuna companies including Starkist, Bumble Bee and Chicken of the Sea. The slogan is ironically fitting because it is a wonder why tuna is so marketable when it is a fish species that accumulates relatively high levels of methylmercury. Its ever-present availability to the consumer is on the increase and this is problematic because that means the potential for mercury poisoning is too.
Mercury is naturally-occurring AND a pollutant
Our world’s oceans contain millions of tons of methylmercury, an organic form of mercury. Its presence occurs naturally in the sea from environmental processes such as volcanic eruptions and forest fires, but the levels have been augmented by residual waste from coal plants and other industrial pollutants from metal smelting, chlorine and cement plants making their way into the waters too. Coal plants add the greater part of the equation, with approximately 50 tons of mercury being introduced into the environment in recent years according to the EPA.
The effort to reduce mercury emissions in the U.S. from coal-burning plants has been on the agenda since the 1970’s with the advent of the Clean Air Act. However, a breakthrough was made in March 2011, when the first national standard was proposed to install smokestack scrubbers and other control technology needed to retrofit coal plants. Nearly half of the nation’s more than 400 coal plants have some form of control technology, but now all the plants should be addressed if the proposal is enacted.
The pollution controls may slowly help remove mercury emissions from entering the habitats of fish, but the time for any significant change to take place is likely to take years or ultimately be ineffective. Additionally, fish will still carry methylmercury in their bodies.
Tuna ranks high on the food chain for mercury
Methylmercury is a toxic heavy metal that binds to proteins such as fish tissue and accrues in fish bodies over the span of their lives. The higher the fish is in the food chain, the more accumulation, a process known as biomagnification. Shark, swordfish, marlin and tuna all build up methylmercury in their bodies; but tuna fish, especially albacore, is of particular concern because tuna is the most widely-eaten fish in America.
The Natural Resources Defense Council has stated that “the most common way Americans are exposed to mercury is through tuna fish.â€
Albacore tuna poses the greatest risk
There are different varieties of tuna that are caught and processed for supermarkets and restaurants including skipjack, bigeye, bluefin, yellowfin and albacore. Bigeye tuna, also known as ahi, contains a very high mercury content. Yellowfin and albacore tuna are ranked high in mercury content whereas all other varieties of tuna are within the moderate level. These measures have been set by the FDA and EPA to protect the consumer.
Among these, albacore poses the greatest risk to the consumer because of how readily available it is, especially in the tin can on market shelves. Albacore that is packaged in cans is marked “white chunk†whereas those that are labeled “chunk light†tend to be comprised of the smaller skipjack tuna. When compared to chunk light canned tuna, albacore was found to contain 3 times more methylmercury content, as found by the FDA in 2003.
The health risk in eating too much albacore lies in its size and the methylmercury content that coincides with it. The albacore tuna typically caught by fishermen weigh up to 79 pounds with an average length of 47 inches. In addition to size, are their large carnivorous appetites and according to the National Oceanic Atmospheric Administration (NOAA) “they eat an enormous amount of food to fuel their high metabolism, sometimes consuming as much as 25 percent of their own weight every day.†What this implies is the rate of biomagnification is high since the tuna fish is exposed to a vast number of mercuried fish in its diet on a regular basis.
To add, the NOAA also states that “mercury levels largely depend on the age and size of tuna when caught and independent research suggests that smaller, younger albacore that are caught by troll and pole-and-line fishermen generally have lower mercury levels than the larger, long line-caught albacore.†Safe serving sizes are difficult to discern
Exposure to mercury primarily affects a person’s brain and nervous system. To safeguard health, the consumer should be aware of how much tuna they are eating. The safest serving size of tuna can be challenging to discern, especially in regards to what is appropriate for children and mothers. It is also important to note that those with developmental deficits should be cautious with how much tuna they eat because of mercury’s affect on brain function and retention. Furthermore, the implications of over-consuming tuna lie in the half-life of mercury, which happens to be 50 days. In other words, the levels of mercury in the human blood stream only begin to decline and be excreted 50 days after exposure.
Heart healthy benefits can be found elsewhere
Much of the push to eat tuna is attributed to the benefits it provides for a healthy heart in addition to its role in weight loss. It is low in fat and cholesterol, offers a rich supply of omega-3 fatty acids and provides a good supply of protein to the diet. In spite of these paybacks, mercury remains to be an issue, especially since the amounts are typically unknown in servings of tuna and can vary.
Currently, the USDA recommends eating 8 ounces of fish each week to ensure that the American public is receiving the heart healthy benefits that fish offers. This dietary recommendation can be met by eating seafood that is low in mercury such as wild salmon, catfish, trout, tilapia, whiting, pollock, perch, herring, anchovies, sardines, sole, shrimp, squid, oyster, clams and crab.
