According to DNA Barcoding; New Research Provides Insight Into Healthier Consumption of Sushi finds Mercury Is Higher in Some Tuna Species

New research showing that that mercury levels are higher in some species of tuna could help consumers minimize their consumption of the silvery metal in their sushi and provide a powerful new tool for regulatory organizations. The new research -- combining DNA barcoding at that American Museum of Natural History with analysis of mercury content at Rutgers University -- is published in Biology Letters early online edition and shows surprisingly that tuna sushi purchased in supermarkets might be healthier than that from restaurants. The sushi made for supermarkets tends to be yellowfin tuna.

"We found that mercury levels are linked to specific species," says Jacob Lowenstein, a graduate student affiliated with the Museum. "So far, the U.S. does not require restaurants and merchants to clarify what species they are selling or trading, but species names and clearer labeling would allow consumers to exercise greater control over the level of mercury they imbibe."

"People who eat fish frequently have a particular need to know which species may be high in contaminants," says Michael Gochfeld, professor at Robert Wood Johnson Medical School. "Some agencies have been afraid that any mention of contaminants will discourage people from eating any fish.

Sushi samples for this research project were taken from 54 restaurants and 15 supermarkets in New York, New Jersey, and Colorado. The results are based on 100 samples, all of which were identified with DNA barcoding as either bigeye tuna (Thunnus obesus), yellowfin tuna (Thunnus albacares), or bluefin tuna species (Thunnus maccoyii, Thunnus orientalis, and Thunnus thynnus). All samples were tested for relative mercury content.

Combining mercury content and species identification in this study shows that all species exceed or approach levels permissible by Canada, the E.U., Japan, the U.S., and the World Health Organization. Mercury levels are significantly higher in bluefin akami (sushi from lean, dark red tuna) and all bigeye tuna samples than in bluefin toro (sushi from fatty tuna) and yellowfin tuna akami samples. This is probably because mercury accumulates differently in different tissue types: mercury has an affinity for muscle and not fatty tissue, so the leanest fish tend to have the highest concentration.

But there also seem to be other factors in play. Although yellowfin tuna is very lean, this species tends to have lower accumulation of mercury, likely because yellowfin are typically smaller than other tuna and are harvested at a younger age. Furthermore, yellowfin are tropical and do not thermoregulate like the warm-blooded bigeye tuna and bluefin tuna. Because bigeye and bluefin species eat three times more than yellowfin to maintain their energy level, they might bioaccumulate, or slowly increase the level of toxins over time.

"Although levels are highest in top-level predatory fish, some fish that are lower on the food chain have high levels," says Joanna Burger, professor at Rutgers University. "The levels of mercury in some tuna are sufficiently high to provide a health risk both to the fish themselves and to the predators that eat them, including humans, particularly those who eat fish frequently."

"We show how you can use DNA as a tool to uncover patterns of species-specific bioaccumulation," says Sergios-Orestis Kolokotronis, a geneticist at the Sackler Institute for Comparative Genomics at the Museum. "This is one of first applications of DNA barcodes in a non-academic setting -- using this method in any human health context and not just for determining whether barcodes can quickly and accurately identify a species."

In addition to Kolokotronis, Gochfeld, Burger, and Lowenstein, authors include George Amato, director of the Sackler Institute for Comparative Genomics at the Museum, and Christian Jeitner of the Environmental and Occupational Health Sciences Institute at Rutgers University. This research was funded by the Alfred P. Sloan Foundation, the Richard Lounsbery Foundation, Columbia University, Rutgers University, and the National Institute for Environmental Health Sciences. The New York Times' food editor Marian Burros collected 20 of the samples for a story on mercury in sushi which were later barcoded and included in this analysis.

Jacob H. Lowenstein, Joanna Burger, Christian W. Jeitner, George Amato, Sergios-Orestis Kolokotronis, and Michael Gochfeld. DNA barcodes reveal species-specific mercury levels in tuna sushi that pose a health risk to consumers. Biology Letters, 2010; DOI: 10.1098/rsbl.2010.0156

Mercurial Tuna: Study Explores Sources of Mercury to Ocean Fish

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 journalEnvironmental 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.

Study Explores Sources of Mercury to Ocean Fish

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.

'Fingerprinting' Method Reveals Fate of Mercury in Arctic Snow

A study by University of Michigan researchers offers new insight into what happens to mercury deposited onto Arctic snow from the atmosphere.

The work also provides a new approach to tracking mercury's movement through Arctic ecosystems.
Mercury is a naturally occurring element, but some 2000 tons of it enter the global environment each year from human-generated sources such as coal-burning power plants, incinerators and chlorine-producing plants.
"When released into the atmosphere in its reduced form, mercury is not very reactive. It can float around in the atmosphere as a gas for a year or more, and it's not really an environmental problem at the concentrations at which it occurs," said Joel Blum, the John D. MacArthur Professor of Geological Sciences.
But once mercury is oxidized, through a process that involves sunlight and often the element bromine, it becomes very reactive. Deposited onto land or into water, the 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. In wildlife, exposure to methylmercury can interfere with reproduction, growth, development and behavior and may even cause death. Effects on humans include damage to the central nervous system, heart and immune system. The developing brains of young and unborn children are especially vulnerable.
The research is described in a paper published online Feb. 7 in the journal Nature Geoscience.
In the Arctic, mercury remains in its benign gaseous form through the dark winter, because there's no sunlight to drive oxidation and little bromine to catalyze the process. But in polar springtime, that all changes. As sea ice breaks up, water vapor rises in great clouds through the openings in the ice, bringing with it bromine from the sea water. The bromine enters the atmosphere, where it conspires with sunlight to convert mercury gas into the reactive form. The activated mercury sticks to snowflakes and ice crystals in the air and travels with them onto the surface of the snow.
This leads to what's known as a mercury depletion event. The normally steady levels of mercury in the atmosphere quickly drop to near zero, as concentrations of mercury on the surface of the snow rise to extremely high levels.
"When we first started observing these events, we didn't know how much of that mercury returned back to the atmosphere, so the high level of mercury in snow was a great concern," Blum said. "But the more we learned, the more we realized that the sunlight shining on the snow typically will cause much of the oxidized mercury to become reduced and return to the atmosphere as a gas. And it turns out that its re-release to the atmosphere has a striking "fingerprint' that we can use to study the progress of this reaction through time."
The fingerprint is the result of a natural phenomenon called isotopic fractionation, in which different isotopes (atoms with different numbers of neutrons) 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.
In the work described in the Nature Geoscience paper, the researchers confirmed, through sample collection and experiments, that MIF occurs during the sunlight-driven reactions in snow, resulting in a characteristic MIF fingerprint that is absent in atmospheric mercury.
"This finding allowed us to use the MIF fingerprint to estimate how much mercury was lost from the snowpack and how much remained behind, with the potential to enter Arctic ecosystems," said U-M graduate student Laura Sherman, the paper's first author. "Our experiments showed that a significant portion of mercury deposited to snow was re-emitted. Any mercury that is not re-emitted is likely to retain the unique fingerprint, so we hope future researchers will be able to use our discovery to track mercury through Arctic ecosystems."
Sherman and Blum's coauthors on the paper are former U-M graduate student Kelsey Johnson; Gerald Keeler and James Barres of the U-M Air Quality Laboratory; and Thomas A. Douglas of the Cold Regions Research and Engineering Laboratory in Fort Wainwright, Alaska.
The research was funded by the National Science Foundation and the Office of Naval Research.

Key To How Bacteria Clear Mercury Pollution Revealed

Mercury pollution is a persistent problem in the environment. Human activity has lead to increasingly large accumulations of the toxic chemical, especially in waterways, where fish and shellfish tend to act as sponges for the heavy metal.

It's that persistent and toxic nature that has flummoxed scientists for years in the quest to find ways to mitigate the dangers posed by the buildup of mercury in its most toxic form, methylmercury.
A new discovery by scientists at the University of Tennessee, Knoxville, and Oak Ridge National Laboratory, however, has shed new light on one of nature's best mercury fighters: bacteria.
"Mercury pollution is a significant environmental problem," said Jeremy Smith, a UT-ORNL Governor's Chair and lead author of the new study. "That's especially true for organisms at or near the top of the food chain, such as fish, shellfish, and ultimately, humans. But some bacteria seem to know how to break down the worst forms of it. Understanding how they do this is valuable information."
Scientists have known that a specific enzyme, known as MerB, gives the bacteria the ability to convert methylmercury into a less-toxic form of mercury that poses substantially less environmental risk, a trait that lets them survive in mercury-rich environments. Finding out how this enzyme works potentially may be a viable way to combat methylmercury.
The UT Knoxville and ORNL researchers, working with colleagues from the University of Georgia and University of California, San Francisco, were able to determine the mechanism -- at the most detailed level -- of how the MerB enzyme breaks apart the dangerous methylmercury molecule.
The scientists used high-performance computers to determine how the three-dimensional structure of the enzyme uses a sort of one-two-three punch to break apart a key link in the methylmercury, between mercury and carbon atoms. Once that bond is broken, the resulting substance is on the way to becoming substantially less harmful to the environment.
Knowing the exact layout of atoms within both the methylmercury and the MerB enzyme, the researchers found out how the enzyme creates an electric field that shifts around electrons in the methylmercury, priming the toxin for deconstruction. The research is a feat that would have been impossible only a year ago. By using increasingly powerful tools, scientists are able to see much more clearly how the "puzzle pieces" of chemical reactions interact.
The next challenge researchers face will be to find a way to take this new understanding of how methylmercury can be broken down and apply it in an ecosystem at large. At least in concept, using these types of bacteria or hijacking the chemical principles they use may provide a way to combat the buildup of methylmercury.
"There's definitely more work to be done in finding ways to build on what we've learned," said Jerry Parks, an ORNL staff scientist and co-author of the study. "But, we're optimistic that these findings can lead to a productive way to address mercury in the environment."
Journal reference:
Parks et al. Mechanism of Hg−C Protonolysis in the Organomercurial Lyase MerB. Journal of the American Chemical Society, 2009; 131 (37): 13278 DOI: 10.1021/ja9016123
Adapted from materials provided by University of Tennessee at Knoxville, via EurekAlert!, a service of AAAS.

Oceanographers Examine Mercury Levels Of Pelagic Fish In Hawaii

In the open ocean, species of large predatory fish will swim and hunt for food at various depths, which leads to unique diets in these fish. Oceanographers and geologists in the School of Ocean and Earth Science and Technology (SOEST) at the University of Hawaiʻi at Mānoa (UHM) and colleagues have found that those fish that hunt deeper in the open ocean have higher mercury concentrations than those that feed near the surface of the ocean because their deep water food has higher mercury.

This research was detailed in the August 18th early edition of the prestigous journal the Proceedings of the National Academy of Sciences.
Mercury is a naturally-occurring trace element distributed throughout the Earth's oceans, land and air. The general public is interested in mercury levels in fish because the organic form, methylmercury, can be toxic at elevated levels if ingested by humans and animals.Mercury enters open ocean food webs, where it bioaccumulates, leading to higher levels in large predatory animals.
Researchers looking at mercury levels in the open ocean have indicated that deeper waters have elevated levels relative to the surface waters. "Bu! ilding o n this information, we thought that deeper-dwelling open ocean animals might have more mercury, as well as the predatory fishes that feed on them," says Anela Choy, a Department of Oceanography Graduate Student at UHM and lead author in this study. This was indeed the case, and the results of their work show that large pelagic fish like bigeye tuna and swordfish that feed deeper in the ocean have elevated total mercury levels relative to their shallower-dwelling counterparts like yellowfin tuna and mahi-mahi. "We show that this is because the food items that they eat also have varying levels of mercury", continues Choy. "Deeper-living micronekton prey (small fishes, squids, and crustaceans) have higher mercury levels relative to more surface-dwelling prey animals. This is important knowledge for scientists studying animals in the open ocean because it helps them to understand how energy and matter cycle, as well as show who is eating who in the vast, blue water environment. Although not the focus of this study, the results may also help provide information to the fish-consuming public on mercury levels in popular commercial species."
To study the mechanisms governing bioaccumulation in open ocean fish, the researchers, who also included Brian N. Popp and Jeffrey C. Drazen, also from UHM, and John Kaneko from the Honolulu company PacMar Inc, collected nine predatory pelagic fish species with different diets in waters surrounding Hawaiʻi, along with a representation of the types of prey these fishes eat. The predatory fish collected represented a wide variety of depths at which they search for food, varying from shallow-ranging predators (0 – 300 meters) to deep-ranging predators (up to 1000 meters). Total mercury levels of these fish were measured, along with an analysis of animals in their stomachs. The authors found that while the sex of a fish and the location where a fish was caught d! id not a ffect mercury concentrations, the size, age and species of fish did. However, for similar sized fish of different species, deeper-ranging predators still had more mercury than shallow-ranging ones. This study shows for the first time, that in addition to the size and age of a fish, or where it swims/lives, that the depth at which a fish feeds influences the amount of mercury it has in it's tissues.
"After looking more closely at these different mid-water prey organisms, a number of interesting questions have opened up," says Choy. "As these organisms are the primary food items for large pelagic fishes that humans like to eat, we need to understand more about how they fit into the open ocean ecosystem in order to sustainably manage our fish populations."
It is important to understand that ocean biology is connected across depths by the movements and hunting behaviors of animals. "The deep sea is remote, hard to study, and often ignored but our results clearly show how its biology is directly connected to human interests, both fishing and health," says Drazen. "Some of the fishes we enjoy at the dinner table grew on a diet of strange and exotic creatures from 1000s of feet deep in the ocean."
The original research was funded by University of Hawaiʻi Sea Grant College Program at UHM, the State of Hawaiʻi, JIMAR (Pelagic Fisheries Research Program (PFRP)), and the National Oceanographic and Atmospheric Administration. The need for a detailed study came after Popp attended a PFRP meeting on the UHM campus and he saw a data table from the State Department of Health of mercury concentrations in Hawaiian pelagic fishes that was published in the newspaper The Honolulu Advertiser. "The table was very crude showing only the average and range of mercury contents in each fish," says Popp." The fishes were listed from lowest m! ercury a t the top and highest mercury at the bottom -- it hit me that the order in the list roughly followed the depth the fish are typically caught in the ocean." Fortunately for Popp and Drazen, Choy, who had completed her undergraduate degree and was doing consulting work within the local seafood industry, and was also interested in this topic. Says Choy, "after interacting with the public, I found that many people were concerned with mercury levels in fish, and I eventually became interested in the oceanographic/ecological aspect of it."
The researchers have recently received funding from the Pelagic Fisheries Research Program, within the Joint Institute for Marine and Atmospheric Research (JIMAR) at UHM to continue using mercury, along with other chemical tracers to elucidate the structure and function of the open ocean food web in Hawaiian waters. Concludes Choy, "We hope this will provide crucial information for ecosystem-based fishery managers and ecosystem modelers."
Journal reference:
Choy et al. The influence of depth on mercury levels in pelagic fishes and their prey. Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0900711106
Adapted from materials provided by University of Hawaii at Manoa.

Landmark U.S. Geological Survey Study

A new landmark study published today documents for the first time the process in which increased mercury emissions from human sources across the globe, and in particular from Asia, make their way into the North Pacific Ocean and as a result contaminate tuna and other seafood. Because much of the mercury that enters the North Pacific comes from the atmosphere, scientists have predicted an additional 50 percent increase in mercury in the Pacific by 2050 if mercury emission rates continue as projected."This unprecedented USGS study is critically important to the health and safety of the American people and our wildlife because it helps us understand the relationship between atmospheric emissions of mercury and concentrations of mercury in marine fish," said Secretary of the Interior Ken Salazar. "We have always known that mercury can pose a risk, now we need to reduce the mercury emissions so that we can reduce the ocean mercury levels.""This study gives us a better understanding of how dangerous levels of mercury move into our air, our water, and the food we eat, and shines new light on a major health threat to Americans and people all across the world," said EPA Administrator Lisa P. Jackson. "With this information in hand, plus our own mercury efforts, we have an even greater opportunity to continue working with our international partners to significantly cut mercury pollution in the years ahead and protect the health of millions of people."Water sampling cited in the study shows that mercury levels in 2006 were approximately 30 percent higher than those measured in the mid-1990s. This study documents for the first time the formation of methylmercury in the North Pacific Ocean. It shows that methylmercury is produced in mid-depth ocean waters by processes linked to the "ocean rain." Algae, which are produced in sunlit waters near the surface, die quickly and "rain" downward to greater water depths. At depth, the settling algae are decomposed by bacteria and the interaction of this decomposition process in the presence of mercury results in the formation of methylmercury. Many steps up the food chain later, predators like tuna receive methylmercury from the fish they consume.One unexpected finding from this study is the significance of long-range transport of mercury within the ocean that originates in the western Pacific Ocean, off the coast of Asia."Mercury researchers typically look skyward to find a mercury source from the atmosphere due to emissions from land-based combustion facilities. In this study, however, the pathway of the mercury was a little different. Instead, it appears the recent mercury enrichment of the sampled Pacific Ocean waters is caused by emissions originating from fallout near the Asian coasts. The mercury-enriched waters then enter a long-range eastward transport by large ocean circulation currents," said USGS scientist and coauthor David Krabbenhoft.Scientists sampled Pacific Ocean water from 16 different sites between Honolulu, Hawaii and Kodiak, Alaska. In addition, the scientists constructed a computer simulation that links atmospheric emissions, transport and deposition of mercury, and an ocean circulation model.In the United States, about 40 percent of all human exposure to mercury is from tuna harvested in the Pacific Ocean, according to Elsie Sunderland, a coauthor of the study. Methylmercury is a highly toxic form of mercury that rapidly accumulates in the food chain to levels that can cause serious health concerns for those who consume the seafood. Pregnant women who consume mercury can pass on life-long developmental effects to their children. That is why in 2004 EPA and FDA issued the landmark Joint Guidance on the Consumption of Fish specifically targeted towards pregnant women and nursing mothers. Previous studies show that 75 percent of human exposure worldwide to mercury is from the consumption of marine fish and shell fish.Scientists have known for some time that mercury deposited from the atmosphere to freshwater ecosystems can be transformed (methylated) into methylmercury, but identifying the analogous cycles in marine systems has remained elusive. As a result of this study we now know more about how the process which leads to the transformation of mercury into methylmercury.The paper, "Mercury sources, distribution and bioavailability in the North Pacific Ocean--Insights from data and models and information on other USGS mercury research, is available online at http://toxics.usgs.gov/investigations/mercury.html.The study appeared today in Global Biogeochemical Cycles, which is published by the American Geophysical Union. In addition to USGS mercury expert David Krabbenhoft, the authors include Elsie Sunderland, Harvard University; John Moreau, University of Melbourne, Australia (until recently a USGS, NRC Post Doctoral Candidate);William Landing, Florida State University; and Sarah Strode, Harvard University.U.S. Department of the Interior

Climate change may increase mercury levels in seals

Climate change in the Arctic may be boosting levels of highly toxic mercury in seals, one of the most commonly eaten traditional foods in the North. A new study published in the journal Environmental Science and Technology has found a strong correlation between mercury in seal meat and shrinking sea ice, one of the most visible and well-publicized consequences of global warming. "Sea ice patterns and contamination sources of ringed seals observed here suggest that the net outcome of longer ice-free seasons in the Arctic may lead to higher mercury levels in circumpolar seal populations," the report says. Levels of mercury, a potent nerve poison, have long been rising in the North as emissions from sources such as coal-burning power plants in southern latitudes drift into the Arctic and remain. That increase has been reflected in animals such as beluga whales and Arctic seabirds. But seals haven't shown a long-term increase. Instead, their mercury levels fluctuate from year to year. In an attempt to understand those changes, scientists at the Department of Fisheries and Oceans in Winnipeg compared levels of mercury in ringed seals from Prince Albert Sound off Victoria Island in the High Arctic to annual number of ice-free days. They found mercury levels increase after any significant difference from the average. "You get this amazing correlation, where it seems to suggest that concentrations (of mercury) that you measure in the ringed seal are associated with sea ice extent," said Gary Stern, one of the co-authors of the paper. The link between the two, suggests Stern, is the Arctic cod. Cod thrive in low ice years, providing a banquet for hungry seals. But the fish concentrate the minute amounts of mercury found in everything they eat and pass that concentration along to their hunters. Seals prefer cod to just about anything else, so Stern says that when they eat more of them, they wind up with more mercury in their bodies. In years when the ice cover is heavy, only the older cod survive. That means that the only cod available to the seals are the ones with relatively high mercury levels, says Stern. "If you have more ice you have higher concentrations and if you have less ice you have higher concentrations." More ice than usual, however, is getting to be a less and less common event in the Arctic. Sea ice is in long-term decline. Last February, scientists said the total extent of Arctic waters covered by ice was about 287,000 square kilometres less than average. Stern says the next step is to return to Victoria Island and see if seals actually do eat more cod in low-ice years. He emphasizes that while seals are still considered a safe and healthy part of northern diets, the link between sea ice and mercury means health officials will have to keep a close eye on the animals. "It's important for us to continue to monitor, because if the levels are going up we want to make sure." Still, the unexpected link between sea ice and mercury levels offers an important lesson in how climate change can produce surprising effects that directly effect how people live in their environment, says Stern. "As we lose more ice, as the climate seems to warm, especially in the North, we really do need to keep monitoring this."

How Mercury Gets into our Seafood

The US Geological Survey published a study today that describes the mechanism by which anthropogenic mercury gets into the seas and into the seafood we eat. While it has been surmised that human use and emissions of Mercury were the source of mercury in the oceans and seafood, the mechanism by which anthropogenic mercury gets there has not been known.A new landmark study published today documents for the first time the process in which increased mercury emissions from human sources across the globe, and in particular from Asia, make their way into the North Pacific Ocean and as a result contaminate tuna and other seafood. Because much of the mercury that enters the North Pacific comes from the atmosphere, scientists have predicted an additional 50 percent increase in mercury in the Pacific by 2050 if mercury emission rates continue as projected."This unprecedented USGS study is critically important to the health and safety of the American people and our wildlife because it helps us understand the relationship between atmospheric emissions of mercury and concentrations of mercury in marine fish," said Secretary of the Interior Ken Salazar."This study gives us a better understanding of how dangerous levels of mercury move into our air, our water, and the food we eat, and shines new light on a major health threat to Americans and people all across the world," said EPA Administrator Lisa P. Jackson. "With this information in hand, plus our own mercury efforts, we have an even greater opportunity to continue working with our international partners to significantly cut mercury pollution in the years ahead and protect the health of millions of people."One unexpected finding from this study is the significance of long-range transport of mercury within the ocean that originates in the western Pacific Ocean, off the coast of Asia. Scientists sampled Pacific Ocean water from 16 different sites between Honolulu, Hawaii and Kodiak, Alaska. In addition, the scientists constructed a computer simulation that links atmospheric emissions, transport and deposition of mercury, and an ocean circulation model. ENN