Tuna Surprise: Over One Third of Mercury Exposure From This Fish, New Study Finds

/PRNewswire/ -- A new study ranking exposure risks from methylmercury finds that tuna accounts for over one third of total mercury exposure from seafood consumption in the United States. These key findings were published in a peer-reviewed paper by Dr. Edward Groth III, "Ranking the contributions of commercial fish and shellfish varieties to mercury exposure in the United States: Implications for risk communication," and appearing in the April 2010 issue of Environmental Research.

"Canned tuna is the number one fish product consumed in the U.S. today at just under 3 pounds per capita per year," said Michael Bender, director of the Mercury Policy Project. "Based on these new findings, tuna is also the number one mercury exposure risk."

Tuna contributes 37% of the total mercury in the seafood supply -- almost six times as much as the combined total of the four highest mercury-laden fish: swordfish, shark, king mackerel and Gulf tilefish, according to the study.

"Eating tuna can be a toxic gamble, especially for pregnant women, mothers, babies and children," said Buffy Martin Tarbox, Campaign Coordinator for GotMercury.org, based in Forest Knolls, CA.

Groth's paper explains seafood varieties differ by over 120-fold in average mercury content, so which fish you choose drives your mercury exposure. For anyone who eats fish twice a week or more -- not just mothers-to-be -- choosing low-mercury fish is an important health strategy.

"Unfortunately," Groth notes, "most consumers have no idea which fish are high in mercury and should be avoided, or which are low in mercury and are safe to consume."

Canned "light" tuna, the most popular fish in the American diet, has an above-average mercury level, and some "light" tuna has even higher levels. Canned albacore (white) tuna and tuna steaks have still higher average mercury levels. "Women who are trying to minimize their mercury exposure should avoid all forms of tuna," says Groth.

Dr. Groth's study also found that two-thirds of the seafood supply and nine of the 11 most consumed fish and shellfish are low or very low in mercury. So if consumers know what to pick, they can easily find low-mercury alternatives.

To view an abstract of Dr. Groth's paper and also his chart grouping 51 fish varieties into six categories by mercury content, visit: www.mercurypolicy.org

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FDA Seeks Permanent Injunction Against Sharkco Seafood International Inc.

The U.S. Food and Drug Administration (FDA) is seeking a permanent injunction against Sharkco Seafood International Inc., located in Venice, La. The injunction is intended to stop the seafood processing company from distributing scombrotoxin-forming fish in interstate commerce. Consumption of scombrotoxin-forming fish that are not properly preserved or refrigeratedcan result in scombroid food poisoning, a foodborne illness that results from eating spoiled or decayed fish. Scombrotoxin-forming fish most commonly include mackerel, sardines, tuna, bluefish, and mahi mahi.

The government’s complaint, filed today by the United States Attorney’s Office for the Eastern District of Louisiana charges Sharkco Seafood and its owners, Khai Q. Nguyen and Tuan Q. Nguyen, with violating the Federal Food, Drug, and Cosmetic Act by failing to establish and implement an adequate Hazard Analysis and Critical Control Point (HACCP) plan for their scombrotoxin-forming fish. FDA requires all seafood processors and distributors to have a HACCP plan that determines and monitors food safety hazards associated with their products.

“FDA repeatedly warned and tried to work with Sharkco Seafood,” said Michael Chappell, acting associate commissioner for regulatory affairs at FDA. “The company had ample time to take correction action, which it failed to do. An effective seafood HACCP plan is critical to safeguard the health of the American people. We will take prompt action against companies whose poor business practices could jeopardize the public health.”

According to the government’s complaint, FDA inspections showed that the defendants failed to have an adequate written HACCP plan for their scombrotoxin-forming fish operation, despite numerous warnings by FDA. The formation of scombrotoxin can be adequately controlled when fish are appropriately preserved or refrigerated. Once formed, however, scombrotoxin cannot be removed or destroyed by washing, freezing, or cooking the affected fish.

No illnesses have been associated with Sharkco Seafood’s scombrotoxin-forming fish products. The company produces other seafood products, which are not affected by this action.

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How Mercury Becomes Toxic In The Environment

TT Note: With the recent headlines of fish contaminated with mercury along many of the southeast coastlines, we thought you'd be interested in learning more about the way it happens in nature.

Naturally occurring organic matter in water and sediment appears to play a key role in helping microbes convert tiny particles of mercury in the environment into a form that is dangerous to most living creatures.

This finding is important, say Duke University environmental engineers, because it could change the way mercury in the environment is measured and therefore regulated. This particularly harmful form of the element, known as methylmercury, is a potent toxin for nerve cells. When ingested by organisms, it is not excreted and builds up in tissues or organs.

In a series of laboratory experiments, Amrika Deonarine, a graduate student in civil and environmental engineering at Duke’s Pratt School of Engineering, found that organic matter and chemical compounds containing sulfur – known as sulfides -- can readily bind to form mercury sulfide nanoparticles. Since they are more soluble than larger particles, these nanoparticles may be the precursors to a process known as methylation.

“When the organic material combines with the mercury, it prevents the particle from accumulating with other mercury particles and growing larger,” said Deonarine, who presented the results of her analysis at the summer annual scientific sessions of the American Chemical Society (ACS) in Washington, D.C.

“Since the mercury remains in a nanoparticle size, it can easily collect on the surface of microbes where any mercury that dissolves can be taken in by the microbes,” Deonarine said. “Without the organic matter, the mercury sulfide nanoparticles would grow too large and become insoluble, thus reducing the availability of mercury for microbial methylation.”

It is while inside the microbe that the mercury is converted into the harmful methylmercury form, the researchers said.

These reactions can only take place in cold water environments with little to no oxygen, such as the zone of sediment just below the bottom of a body of water. Other such anaerobic environments can also be found in waste water and sewage treatment systems, the researchers said.

“The exposure rate of mercury in the U.S. is quite high,” said Heileen Hsu-Kim, Duke assistant professor of civil and environmental engineering and senior member of the research team. “A recent epidemiological survey found that up 8 percent of women had mercury levels higher than national guidelines. Since humans are on top of the food chain, any mercury in our food accumulates in our body.”

Because fish and shellfish have a natural tendency to store methylmercury in their organs, they are the leading source of mercury ingestion for humans. Mercury is extremely toxic and can lead to kidney dysfunctions, neurological disorders and even death. In particular, fetuses exposed to methylmercury can suffer from these same disorders as well as impaired learning abilities.

There are many ways mercury gets into the environment, with the primary sources being the combustion of coal, the refining of such metals as gold and other non-ferrous metals, and in the gases released during volcanic eruptions. The air-borne mercury from these sources eventually lands on lakes or ponds and can remain in the water or sediments.

“These initial laboratory findings could have far-reaching implications,” Hsu-Kim said. “That these reactions can take places in anaerobic environments suggests that the old paradigm of testing for toxic metals in sediments may provide an incomplete picture of how much methylmercury is there.”

The researchers plan to continue their studies with other types of organic matter and for longer periods of time.

For her presentation and paper, Deonarime was one of six recipients of the C. Ellen Gonter Environmental Chemistry Award, given annually to graduate students.

The research was supported by the federally funded Center for the Environmental Implications of NanoTechnology (CEINT), which is based at Duke, and the ACS’s Petroleum Research fund.

by Richard Merritt
Pratt School of Engineering
Duke University

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