Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Mercurial tuna: Study explores sources of mercury to ocean fish

03.03.2010
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.

Contact: Nancy Ross-Flanigan
Phone: (734) 647-1853

Nancy Ross-Flanigan | EurekAlert!
Further information:
http://www.umich.edu

More articles from Ecology, The Environment and Conservation:

nachricht Waste in the water – New purification techniques for healthier aquatic ecosystems
24.07.2018 | Eberhard Karls Universität Tübingen

nachricht Plenty of habitat for bears in Europe
24.07.2018 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New interactive machine learning tool makes car designs more aerodynamic

Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.

When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...

Im Focus: Robots as 'pump attendants': TU Graz develops robot-controlled rapid charging system for e-vehicles

Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.

Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....

Im Focus: The “TRiC” to folding actin

Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.

Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...

Im Focus: Lining up surprising behaviors of superconductor with one of the world's strongest magnets

Scientists have discovered that the electrical resistance of a copper-oxide compound depends on the magnetic field in a very unusual way -- a finding that could help direct the search for materials that can perfectly conduct electricity at room temperatur

What happens when really powerful magnets--capable of producing magnetic fields nearly two million times stronger than Earth's--are applied to materials that...

Im Focus: World record: Fastest 3-D tomographic images at BESSY II

The quality of materials often depends on the manufacturing process. In casting and welding, for example, the rate at which melts solidify and the resulting microstructure of the alloy is important. With metallic foams as well, it depends on exactly how the foaming process takes place. To understand these processes fully requires fast sensing capability. The fastest 3D tomographic images to date have now been achieved at the BESSY II X-ray source operated by the Helmholtz-Zentrum Berlin.

Dr. Francisco Garcia-Moreno and his team have designed a turntable that rotates ultra-stably about its axis at a constant rotational speed. This really depends...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Within reach of the Universe

08.08.2018 | Event News

A journey through the history of microscopy – new exhibition opens at the MDC

27.07.2018 | Event News

2018 Work Research Conference

25.07.2018 | Event News

 
Latest News

'Building up' stretchable electronics to be as multipurpose as your smartphone

14.08.2018 | Information Technology

During HIV infection, antibody can block B cells from fighting pathogens

14.08.2018 | Life Sciences

First study on physical properties of giant cancer cells may inform new treatments

14.08.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>