Findings published in Proceedings of the National Academy of Sciences by Oak Ridge National Laboratory’s Liyuan Liang and Baohua Gu help explain previously reported seemingly contradictory findings. (ORNL photo by Jason Richards) |
Nature has a bit of a Jekyll and Hyde
relationship with mercury, but researchers at the Department of Energy’s Oak
Ridge National Laboratory have made a discovery that ultimately could help
explain the split personality.
While scientists have known that microbes in
aquatic environments make methylmercury, a more toxic form of mercury that
accumulates in fish, they also know that nature and other types of bacteria can
transform methylmercury to less toxic forms. What they haven’t completely
understood are the mechanisms that cause these transformations in anoxic environments
in nature.
“Until now, reactions between elemental
mercury and dissolved organic matter have rarely been studied in anoxic
environments,” said Baohua Gu of the the lab’s Environmental Sciences
Division.
In a paper published in the Proceedings of the National Academy of
Sciences, a team led by Gu reports that compounds from the decay of organic
matter in aquatic settings affect mercury cycling. Low concentrations of these
compounds can chemically reduce mercury, but as those concentrations increase,
that reaction is greatly inhibited. They performed their experiments by
simulating conditions found in nature.
“This study demonstrates that in anoxic
sediments and water, organic matter is not only capable of reducing mercury,
but also binding to mercury,” said co-author Liyuan Liang. “This
binding could make mercury less available to microorganisms for making
methylmercury.”
The authors also noted that their paper offers
a mechanism that helps explain the seemingly contradictory reports on the
interaction of organic matter and mercury in nature.
Gu and Liang hope this newly gained
knowledge will play a role in helping to understand how mercury cycles in
aquatic and sediment environments and help in informed decision-making for
mercury-impacted sites around the nation.
“Our long-term goal is to understand
the mechanisms controlling the production of methylmercury in the environment,
” Liang said. “This understanding could lead to ways to reduce levels
of mercury in fish as this is a global problem of enormous significance.”
Mercury is distributed around the globe
mainly through the burning of coal, industrial uses and through natural
processes such as volcano eruptions. Various forms of mercury are widely found
in sediments and water.
This research benefits from ORNL’s expertise
in field-to-laboratory geochemistry and microbiology, computational modeling
and simulation, world-class neutron sources and high-performance computing.
Other authors of the paper,
“Mercury reduction and complexation by natural organic matter in anoxic
environments,” are Carrie Miller and Wenming Dong of ORNL and Yongrong
Bian and Xin Jiang, visiting scientists from the Chinese Academy
of Science.
