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GLIN==> UM Research on Tracking Mercury Pollution by Isotope Analysis
- Subject: GLIN==> UM Research on Tracking Mercury Pollution by Isotope Analysis
- From: "Alex J. Sagady & Associates" <email@example.com>
- Date: Sat, 15 Sep 2007 14:47:12 -0400
- Delivered-to: firstname.lastname@example.org
- Delivered-to: email@example.com
- List-name: GLIN-Announce
Sept. 13, 2007
Contact: Nancy Ross-Flanigan, (734) 647-1853, firstname.lastname@example.org
EMBARGOED FOR RELEASE AT 2 P.M. EDT THURSDAY, SEPT. 13, 2007
New fingerprinting method tracks mercury in environment
ANN ARBOR, Mich.---With mercury polluting our air, soil and water and
becoming concentrated in fish and wildlife as it is passed up the
food chain, understanding how the potent nerve toxin travels through
the environment is crucial.
A new method developed at the University of Michigan uses natural
"fingerprints" to track mercury and the chemical transformations it
undergoes. A report on the work is published today in Science Express.
Mercury is a naturally occurring element, but some 150 tons of it
enter the environment each year from human-generated sources in the
United States, such as incinerators, chlorine-producing plants and
coal-fired power plants. Mercury is deposited onto land or into
water, where microorganisms convert some of it to methylmercury, a
highly toxic form that builds up in fish and the animals that eat
them. 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.
Because of such profound and irreversible effects on health and the
environment, "it's very important to understand how and where mercury
transforms into its most toxic forms and how it moves around in the
environment, leading to human and animal exposure," said research
fellow Bridget Bergquist, who is first author on the paper.
"I have often dreamed of how useful it would be if we could mark
individual atoms of mercury with an indelible fingerprint of key
chemical reactions and use this fingerprint to follow them around in
the environment," said co-author Joel D. Blum, who has been working
on the problem for more than a decade. "This is precisely what we
have been able to achieve with the experiments that we're reporting.
Our work opens the door to an entirely new method for tracing mercury
pollution and for investigating mercury behavior in the environment
and in the food chains of humans and other animals."
Bergquist and Blum based their new tracking method on a natural
phenomenon called isotopic fractionation, in which different isotopes
(forms) of mercury react to form new compounds at slightly different
rates, something like bicycle racers in the Tour de France. Some
riders perform better in the mountainous stages of the race and are
separated from the pack due to their strength; others distinguish
themselves on the flat stages of race due to their superior speed.
With mercury isotopes, it's mass, not athletic ability, that dictates
their behavior---in one type of isotopic fractionation, at least. In
this mass-dependent fractionation (MDF), different mercury isotopes
participate differently in chemical reactions, based on their masses.
"While mass-dependent fractionation is a well-known phenomenon in
lighter elements and forms the basis for how we determine such things
as past climates on the Earth and dietary food chains of animals,
mercury was thought to be too heavy for the signal to show up," said
Blum, who is the John D. MacArthur Professor of Geological Sciences.
But in this work, Bergquist and Blum show that mass-dependent
fractionation can be used to track mercury. Because the process is
observed naturally in fish as they grow, the mercury the fish excrete
must have a different isotopic composition than the mercury they take
in, so MDF may reveal how much mercury fish consume, how much they
excrete and how it changes during the fishes' lifetimes.
In the current work, the researchers exploited both MDF and another
type of isotopic fractionation called mass-independent fractionation
(MIF), in which isotopes segregate based not on absolute mass but on
whether their masses are odd or even. Bergquist and Blum discovered
that this type of fractionation occurs only in reactions involving
sunlight, such as those that take place in surface waters and result
in methylmercury being detoxified and released to the atmosphere.
Mass-independent fractionation of mercury and other heavy elements
had been predicted but never carefully documented in nature.
By combining two methods that provide distinct isotope signatures,
Bergquist and Blum came up with a tracking tool that is more powerful
than either one alone.
"We found that fish from a wide range of lakes and from the ocean all
have large degrees of both mass-independent and mass-dependent
isotope fractionation," Bergquist said. "So now we're able to use the
mass-independent isotope signatures to estimate the proportion of
toxic methylmercury at each location that was detoxified and released
to the atmosphere by photochemical reactions, and we're also able to
use the mass-dependent isotope signatures to study the accumulation
of mercury in fish as they age and grow larger. Together the two
signatures provide a label that allows us to understand the sources
of methylmercury to fish and to differentiate fish from different localities."
Using the method in this way illustrates its potential for much wider
application, Blum said. "One example is a complementary study that we
reported at a recent scientific meeting." In that study research
fellow Abir Biswas, working with Bergquist and Blum, found that
mercury in coals from various coal-producing regions around the world
vary in their mass-dependent and mass-independent isotopic
composition. "This suggests that we may be able to use the mercury
isotope studies to distinguish different sources of mercury to the
atmosphere, which has far-reaching practical applications," Blum
said. "In short, this entirely new approach to studying mercury
sources, mobility and toxicity in the environment paves the way for a
wide range of studies that should enhance our understanding of this
important toxin in the environment."
The researchers received funding from the Division of Earth Sciences
of the National Science Foundation and the Turner Postdoctoral
Fellowship from the U-M Department of Geological Sciences.
For more information:
Bridget Bergquist: email@example.com
Science Express: http://www.sciencemag.org/sciencexpress/recent.dtl
Basic information on mercury from the EPA: http://eap.gov/mercury/about.htm
National Science Foundation: http://www.nsf.gov/
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