Mercurial Tuna: Study Explores Sources of Mercury to Ocean Fish

ScienceDaily — With concern over mercury contamination of tuna on the rise and growing information about the health effects of eating contaminated fish, scientists would like to know exactly where the pollutant is coming from and how it's getting into open-ocean fish species.

A new study published in the journal Environmental Science & Technology uses chemical signatures of nitrogen, carbon and mercury to get at the question. The work also paves the way to new means of tracking sources of mercury poisoning in people.

The study, by researchers at the University of Michigan, Harvard School of Public Health, the Louisiana Universities Marine Consortium and the National Institute of Nutrition and Seafood Research in Norway, appears in the journal's March 1, 2010 issue.

Mercury is a naturally occurring element, but some 2,000 tons of it enter the global environment each year from human-generated sources such as coal-burning power plants, incinerators and chlorine-producing plants. Deposited onto land or into water, mercury is picked up by microorganisms, which convert some of it to methylmercury, a highly toxic form that builds up in fish and the animals -- and people -- that eat them.

The primary way people in the United States are exposed to methylmercury is by eating fish and shellfish. Health effects include damage to the central nervous system, heart and immune system, and the developing brains of young and unborn children are especially vulnerable.

In the current study, the researchers wanted to know if tuna and other open-ocean fish pick up methylmercury by eating contaminated fish that live closer to shore or by some other means. They studied 11 species of fish, including red snapper, speckled trout, Spanish mackerel and two species of tuna. Seven of the species studied live in the shallow, coastal waters of the Gulf of Mexico; the two tuna species live far out in the ocean and are highly migratory; the remaining two species spend parts of their lives in both habitats.

It's no mystery how the coastal fish acquire methylmercury, said Joel Blum, who is the John D. MacArthur Professor of Geological Sciences at U-M. "We know that there's a lot of mercury pollution in the coastal zone. A large amount of mercury comes down the Mississippi River, and there's also air pollution and deposition of mercury from the highly industrialized coastal Gulf region." In this environment, methylation occurs in the low-oxygen conditions of the lower water column and sediments, and the methylmercury wends its way up the food web, becoming more concentrated at each step along the way.

"It's much less clear how methylmercury gets into open-ocean fish species, some of which don't come anywhere close to shore but can still have very high levels," said the study's lead author, David Senn, formerly of the Harvard School of Public Health, and now a senior researcher at the Swiss Federal Institute of Aquatic Science and Technology. Scientists have proposed three possibilities.

One is that open-ocean fish visit coastal areas to feed, picking up methylmercury from the coastal food web. Another possibility is that small organisms that acquire methylmercury in coastal regions are washed out to sea, where they enter the open-ocean food web. In the third scenario, mercury is directly deposited into the open ocean, where it undergoes methylation.

By looking at three chemical signatures in the fish -- nitrogen isotopes, carbon isotopes and mercury isotopes -- Senn, Blum and colleagues learned that coastal fish and open-ocean fish are feeding from two separate food webs.

"That rules out the first explanation, that these tuna were getting their methylmercury by feeding off coastal fish," Senn said.

"We think it's unlikely that the mercury is being methylated in coastal sediments and then washed out to the open ocean, so the most likely alternative is that there is deposition and methylation of mercury in the open ocean," Blum said. The finding runs counter to the long-held view that the open ocean is too oxygen-rich to support methylation, but it is consistent with recent studies suggesting more methylation may be occurring in that environment than was previously thought.

"It turns out there are probably low-oxygen microenvironments on tiny particles of organic matter, where methylation may be able to occur," Blum said.

One of the biggest differences the researchers found between coastal and open-ocean fish was in their mercury "fingerprint." The fingerprint is the result of a natural phenomenon called isotopic fractionation, in which different isotopes of mercury react to form new compounds at slightly different rates. In one type of isotopic fractionation, mass-dependent fractionation (MDF), the differing rates depend on the masses of the isotopes. In mass-independent fractionation (MIF), the behavior of the isotopes depends not on their absolute masses but on whether their masses are odd or even.

The researchers found that open-ocean fish have a much stronger MIF fingerprint than do coastal fish, a discovery that opens the door to new ways of analyzing human exposure to mercury.

"We can do an isotopic analysis of the mercury in your hair, and by looking at this mass-independent signal, tell you how much of the mercury is coming from inorganic sources, such as exposure to mercury gas or amalgams in your dental fillings, versus how much is coming from the fish that you eat," Blum said. "We think this could become a widespread technique for identifying sources of mercury contamination."

Senn and Blum's coauthors are Edward Chesney of the Louisiana Universities Marine Consortium; Michael Bank and James Shine of Harvard School of Public Health; and Amund Maage of Norway's National Institute of Nutrition and Seafood Research.

The research was funded by a National Oceanic and Atmospheric Administration grant to Harvard School of Public Health and by the University of Michigan.

Source: http://www.sciencedaily.com/releases/2010/03/100302111918.htm

---

About Oceanic Defense
We are an international non-profit organization with members in over 60 countries, spanning 6 continents with 1 mission; healthy aquatic ecosystems free from human abuse and neglect. Oceanic Defense teaches people to protect our oceans by acting responsibly as consumers and by making smart decisions in our daily lives. Whether we are buying groceries, commuting to work, planning a vacation or advocating within our own communities; each action we take or decision we make either helps or hurts our oceans. We empower people to be part of the solution rather than part of the problem and work together to protect our blue planet.

Join us on Facebook:
www.facebook.com/OceanicDefense
Visit our official website:
www.oceanicdefense.org
Follow us on Twitter:
www.twitter.com/OceanicDefense

How Arctic Food Webs Affect Mercury in Polar Bears

ScienceDaily — With growing concerns about the effects of global warming on polar bears, it's increasingly important to understand how other environmental threats, such as mercury pollution, are affecting these magnificent Arctic animals.

New research led by biogeochemists Travis Horton of the University of Canterbury and Joel Blum of the University of Michigan lays the groundwork for assessing current and future effects of mercury deposition and climate change on polar bears.

The study appears in the December issue of the journal Polar Research.

Mercury is a naturally occurring element, but some 150 tons of it enter the environment each year from human-generated sources such as coal-burning power plants, incinerators and chlorine-producing plants. Deposited onto land or into water, mercury is picked up by microorganisms, which convert some of it to methylmercury, a highly toxic form that builds up in fish and the animals that eat them. As bigger animals eat smaller ones, the methylmercury is concentrated -- a process known as bioaccumulation. Sitting at the top of the food chain, polar bears amass high concentrations of the contaminant.

Although that much is known, the details of how mercury moves through different food webs -- particularly in the Arctic, where snow and ice contribute to mercury deposition -- are not well understood. To tease out that information, Horton, Blum and co-workers studied polar bear hair samples from museum specimens collected in the late 19th and early 20th centuries, before mercury emissions from human-generated sources began to escalate.

By looking at three chemical signatures -- nitrogen isotopes, carbon isotopes and mercury concentrations -- the researchers learned that polar bears get their nutrition (and mercury) from two main food webs. At the base of one web are microscopic plants that float on the surface of the ocean (known as phytoplankton). The foundation of the second web is algae that live on sea ice.

The study showed that polar bears that get most of their nutrition from phytoplankton-based food webs have greater mercury concentrations than those that participate primarily in ice algae-based webs.

While it's tempting to speculate that declining sea ice, due to global warming, may force polar bears to depend more on phytoplankton-based webs, thus increasing their mercury exposure, the study doesn't directly address that issue. It does, however, provide other useful information, said Blum, who is the John D. MacArthur Professor of Geological Sciences and a professor of ecology and evolutionary biology.

"If you want to understand the potential effects of changing ecosystems on polar bears, you need to be aware of the existence of these two food webs, which may possibly be affected by sea ice," Blum said. "This work provides background information that will be important in our in-depth understanding of mercury bioaccumulation in polar bears."

In addition to Horton and Blum, the paper's authors are Zhouqing Xie, who was at U-M when the research was done and now is at the University of Science and Technology of China; Michael Hren, who was at Yale University when the work was done and now is a postdoctoral fellow at U-M; and C. Page Chamberlain of Stanford University.

Source: http://www.sciencedaily.com/releases/2009/12/091208170915.htm

CBS 5 News Anchor Tests Canned Tuna For Mercury

CBS5 - Canned tuna is a healthy source of vitamins and protein, but it also contains some levels of mercury. Whether it's enough to require posted warning signs is being debated in a state appellate court. In the meantime, CBS 5's Sue Kwon conducted her own unscientific experiment tracking consumption of canned tuna and measuring levels of mercury.

The experiment involved eating 20 five-ounce cans of albacore tuna over 20 days and not eating seafood that could contain mercury and impact the experiment.

Canned tuna is packed with lean protein and omega-3 fatty acids which studies show benefit the heart, brain, and eyes.

But even the fishing industry acknowledges, it does contain mercury. It's a chemical that could be toxic at certain levels and erase those benefits as well as cause problems in an unborn baby.

California's Proposition 65 requires warning signs to be posted at the fish counter. The law is intended to protect California citizens from chemicals known to cause cancer or other reproductive harm. Canned tuna companies won a legal fight to be exempt from the law, but now the California Attorney General's office is appealing that court decision.

"We know that methyl mercury is a potent neurotoxin that can harm the unborn baby," said California Deputy Attorney General Susan Fiering. "In Minamata Bay, (poisoning of the 1930s-1960s) mercury caused children to be born with cerebral palsy, with small brains, and undersize brains."

Forrest Hainline who represents the three biggest canners, (Bumblebee, Chicken of the Sea, and Starkist,) said warnings in supermarket aisles would decrease fish consumption and have a negative impact on public health.

"It would be completely conflicting with federal law which wants women to understand that while they are pregnant or may become pregnant, eating fish is good for them and their unborn children," Hainline said.

The problem is doctors really don't know how much tuna it takes for a person to accumulate higher levels of mercury.

While the test sounds risky, she was not pregnant or about to become pregnant and was not expected to hit levels associated with side effects.

After eating 20 cans, a phone call comes from the doctor. Dr. Jane Hightower said, "I want you to stop your experiment. It's not worth the risk."

Dr. Hightower is an expert in mercury poisoning and a known critic of the fishing industry. She is not happy with the National Fisheries Institute website which said canned tuna is "healthy" for pregnant women and they can safely eat 6-ounces or a little over a can a week.

She tells pregnant patients, "Why eat mercury at all when you don't have to? Canned albacore tuna has an average of .35 parts per million and they say tuna is a low mercury fish."

It can be considered "low" if one compares it to the legal mercury limit of 1 part per million set by the Food and Drug Administration. But, the allowed level of mercury in the U.S. is double that of Canada (.5ppm), Europe (.5ppm), and Japan (.4ppm). So elsewhere, canned tuna would not be considered a "low" mercury fish.

The experiment illustrates that even at levels below the federal limit, mercury accumulates in the body reaching what Dr. Hightower and an independent lab flagged as "high" levels in a short period.

At the start of the experiment, Sue Kwon's blood mercury level was low at 4 micrograms per liter. In 10 days, it went to 8.9 micrograms per liter. Then in 10 more days, it climbed to 17.2 micrograms per liter. By day 20, it had quadrupled. "Anytime in a woman's body she reaches a 14 or 15 she stands a chance of knocking IQ points off her child's brain," Hightower said.

If the experiment continued, Dr. Hightower said the mercury would accumulate mercury faster and the level would spike. Hightower said, "You probably would've doubled again in another 10 days and then probably leveled out at in a steady state somewhere in the 50 range."

Hightower's patients with blood mercury levels that high have experienced these symptoms. "They get body aches, joint pain, muscle aches, head ache, trouble sleeping, troubles with thinking and memory, stomach upset," she said.

The canned tuna industry said there are no scientific studies proving a link between mercury levels in fish and specific health effects.

"These are issues that need to be discussed with a doctor not the grocery store checkout clerk or the Safeway manager. It's that simple," Hainline said.

Fiering believes consumers need in-store education materials. "There are a lot of women out there who don't use computers and don't see their doctors regularly and are not getting regular checkups and they're not getting the information they need," she said.

According to the Department of Public Health, 17 micrograms per liter is higher than the average exposure which is about 6 micrograms per liter. The fishing industry recommends eating 2-3 servings of seafood a week including canned tuna. A "serving" of canned tuna is half a can, about enough to top 3 crackers. Obviously, the experiment involved eating more than what's recommended.

Even so, at 17.2 micrograms per liter, Sue Kwon did not feel side effects. But, she is lowering her mercury level by avoiding tuna and sweating it out at the gym. She is continuing to eat fish as recommended for nutrients and health benefits. But, she is making sure to mix the varieties and eating tuna along with fish that do not contain as much mercury.

Source: http://cbs5.com/consumer/tuna.mercury.test.2.951871.html