Mercury’s Rising, Seafood Lovers Beware

Yellowfin Tuna Fish

Tuna like this may have more mercury in its system than previously thought.

Mercury levels are rising in the World’s oceans, but not just according to the thermometer. Scientists are warning that mercury levels in Tuna and other fish are increasing more than previously thought, posing potential danger to seafood lovers.

Researchers from the Woods Hole Oceanographic Institution in Massachusetts published their study in the journal Environmental Toxicology and Chemistry. Carl Lamborg, Paul Drevnick, and Martin Horgan re-evaluated data from an older study about yellowfin tuna that were caught in Hawaii over the past few decades. Their analysis revealed that mercury levels in fish are rising higher than previously thought, at about 3.8 percent a year.

The researchers determined there was no noticeable increase in mercury levels in the tuna from 1971 to 1998, as previously noted. However, between 1998 and 2008, the mercury levels started rising rapidly. The scientists had factored in each fish’s age and weight in their calculations since there would likely be more mercury in bigger, older fish.

While the presence of mercury in fish is nothing new, the data indicates the problem may be worse than previously thought. Scientists had always assumed that mercury in the air, from industrial processes such as burning coal, had made its way into water ecosystems. However, they were unsure how much of that mercury then made its way into the tissues of fish.

Mercury is toxic to animals such as fish and humans, and in high levels it can pose an even greater health risk. The problem is that mercury tends to accumulate in tissues, so as smaller fish take in mercury, the larger fish that eats them collects the mercury from all the smaller fish. Higher up the aquatic food chain, the fish can have greater and greater concentrations of mercury in their body. A small addition of mercury to smaller fish species can have an accelerating effect as it moves up the food chain.

What is concerning about the high mercury levels in the yellowfin tuna is that they are not at the very top of the food chain, yet they still have plenty of mercury in their systems already. Larger, predatory fish such as sharks and swordfish tend to be at the top of an ocean food pyramid.

By the time humans eat fish such as the popular yellowfin tuna, sometimes called Ahi tuna, enough mercury may have accumulated to do harm. Pregnant and breastfeeding women, as well as children, have been warned away from eating too much of certain types of fish because of the potential danger. However, health experts still stress the benefits of eating fish species that are low in mercury, and say that even pregnant women should still eat some fish each week to benefit the developing fetus. Fish tend to be high in Omega-3 fatty acids as well as being a good source of protein. The Natural Resources Defense Council has listed Ahi tuna as a fish that is high in mercury, and recommended that most people should eat it sparingly or avoid eating it. The rising levels or mercury mean that yellowfin tuna could become completely inedible in the near future. At the current rate of mercury accumulation, the tuna could exceed FDA-determined dangerous levels in less than thirty years.

Mercury exposure, specifically methyl mercury, can have negative effects on humans. The metal can affect the brain and nervous system, causing developmental problems and lower IQ in children who are exposed to large amounts. Children and fetuses are most at risk because they are still developing.

Much of the mercury in the ocean around Hawaii may come from overseas industrial activities, such as coal burning and small-scale gold mining, according to some studies. The authors of the tuna study urge more efforts to reduce mercury emissions.

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