Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why mercury is more dangerous in oceans

28.06.2010
Even though freshwater concentrations of mercury are far greater than those found in seawater, it's the saltwater fish like tuna, mackerel and shark that end up posing a more serious health threat to humans who eat them.

The answer, according to Duke University researchers, is in the seawater itself.

The potentially harmful version of mercury – known as methylmercury -- latches onto dissolved organic matter in freshwater, while it tends to latch onto chloride -- the salt -- in seawater, according to new a study by Heileen Hsu-Kim, assistant professor of civil and environmental engineering at Duke's Pratt School of Engineering.

"The most common ways nature turns methylmercury into a less toxic form is through sunlight," Hsu-Kim said. "When it is attached to dissolved organic matter, like decayed plants or animal matter, sunlight more readily breaks down the methylmercury. However, in seawater, the methlymercury remains tightly bonded to the chloride, where sunlight does not degrade it as easily. In this form, methylmercury can then be ingested by marine animals."

Methylmercury is a potent neurotoxin that 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. Because fish and shellfish have a natural tendency to store methylmercury in their organs, they are the leading source of mercury ingestion for humans.

"The exposure rate of mercury in the U.S. is quite high," Hsu-Kim said. "A recent epidemiological survey found that up 8 percent of women had mercury levels higher than national guidelines. Since humans are on the top of the food chain, any mercury in our food accumulates in our body."

The results of Hsu-Kim's experiments, which have been published early online in the journal Nature Geoscience, suggest that scientists and policymakers should focus their efforts on the effects of mercury in the oceans, rather than freshwater.

Her research is supported by the National Institute of Environmental Health Science.

In the past, most of the scientific studies of effects of mercury in the environment have focused on freshwater, because the technology had not advanced to the point where scientists could accurately measure the smaller concentrations of mercury found in seawater. Though the concentrations may be smaller in seawater, mercury accumulates more readily in the tissues of organisms that consume it.

"Because sunlight does not break it down in seawater, the lifetime of methlymercury is much longer in the marine environment," Hsu-Kim said. "However, the Food and Drug Administration and the Environmental Protection Agency do not distinguish between freshwater and seawater."

Mercury enters the environment through many routes, but the primary sources are coal combustion, the refinement of gold and other non-ferrous metals, and volcanic eruptions. The air-borne mercury from these sources eventually lands on lakes or oceans and can remain in the water or sediments.

The key to the sun's ability to break down methylmercury is a class of chemicals known as reactive oxygen species. These forms of oxygen are the biochemical equivalent of the bull in the china shop because of the way they break chemical bonds. One way these reactive oxygens are formed is by sunlight acting on oxygen molecules in the water.

"These reactive forms of oxygen are much more efficient in breaking the bonds within the methylmercury molecule," Hsu-Kim said. "And if the methylmercury is bonded to organic matter instead of chloride, then the break down reaction is much faster."

Tong Zhang, a Ph.D. candidate in Hsu-Kim's laboratory, was first author on the paper.

Richard Merritt | EurekAlert!
Further information:
http://www.duke.edu

More articles from Earth Sciences:

nachricht New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland
19.01.2017 | University of Gothenburg

nachricht Water - as the underlying driver of the Earth’s carbon cycle
17.01.2017 | Max-Planck-Institut für Biogeochemie

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland

19.01.2017 | Earth Sciences

Not of Divided Mind

19.01.2017 | Life Sciences

Molecule flash mob

19.01.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>