Thawing permafrost and contaminated sediment in marine coastal areas pose some of the greatest risks for the production of highly toxic methylmercury, according to findings published in the journal Science Advances.
The discovery of these newly identified locations for methylmercury production builds on previous work in which scientists from the Department of Energy's Oak Ridge National Laboratory reported on two genes in bacteria that convert inorganic mercury into the organic form.
This variety, called methylmercury, is far more dangerous to humans and the environment. Now, scientists from ORNL and the Smithsonian Environmental Research Center have found that these genes are present in microbes from many of the 3,500 environments they examined.
"We looked for genes that we know are involved in microbial mercury methylation - from deep in the ocean to Arctic permafrost to the human gut," said corresponding author Dwayne Elias of ORNL's Biosciences Division. "Using new computational methods, we examined data from thousands of sites around the globe where other scientists had sequenced every gene in that environment."
Elias noted that many of the metagenomes used in the study were obtained from the Joint Genome Institute, and tools from the Integrated Microbial Genomes System aided in the analysis.
While researchers confirmed the presence of the genes of bacteria they suspected could methylate mercury, they found several new and novel bacteria to add to the list. Researchers also looked at 1,500 human and mammalian metagenomes and concluded that there is an extremely low risk of microbial methylation of mercury within the human body. This essentially put to rest concerns raised in their work published in Environmental Science and Technology in 2013 in which they reported this possibility.
With the exception of the mammalian gut, the team found that the mercury methylation genes are abundant in nearly every oxygen-free environment, including rice paddies and marshes, aquatic sediments and certain types of bioreactors. The genes are also abundant in invertebrate digestive tracts and extreme environments. The genes were not typically found in aerated habitats such as the open ocean.
Mercury is a global pollutant released to the atmosphere through coal burning, artisanal (small-scale) mining, industrial uses and some natural processes. Most of the harm comes from methylmercury bioaccumulation, which is the buildup of the element in tissue that occurs when moving up the food chain. Ocean fish are the primary source of methylmercury in human diets worldwide.
"Understanding the source of methylmercury to marine food webs was one of our primary goals in doing this metagenomic analysis," said co-author Cynthia Gilmour of the Smithsonian Environmental Research Center. "We found an abundance of the microbial mercury methylation genes in coastal sediments such as the San Francisco Bay delta and marshes."
Other regions potentially at risk for increased methylmercury production include coastal "dead zones" like the bottom of the Chesapeake Bay and the Mississippi River plume in the Gulf of Mexico.
Elias and colleagues are looking for other microbes able to methylate mercury and are developing a universal model to further explain where this process happens -- and ways to minimize risk to humans and animals.
"While our findings still leave the source of methylmercury acquirement in open ocean fish as a bit of a mystery, it is clear that the primary source of methylmercury to humans is not from making it in our bodies," Elias said.
"It is also quite clear that as the permafrost of today becomes the thawed sediment of tomorrow due to climate change, the risk for substantial levels of methylmercury generation is high given the high gene counts and the continued emission and deposition of mercury in the Arctic."
This finding and previous work by ORNL and the Smithsonian Environmental Research Center explains why methylated mercury is produced in areas where the neurotoxin's presence had puzzled researchers for decades. The toxin, which is the most dangerous form of mercury, damages the brain and immune system and is especially harmful to developing embryos.
Other authors of the paper, titled "Global Prevalence and Distribution of Genes and Microorganism involved in Mercury Methylation," are Mircea Podar, Craig Brandt, Steven Brown, Bryan Crable, Anthony Palumbo and Anil Somenahally of ORNL and Allyson Soren of the Smithsonian Environmental Research Center. The paper is available at http://advances.
UT-Battelle manages ORNL for the DOE's Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.
The Smithsonian Environmental Research Center has studied the science of Chesapeake Bay and coastlines around the globe since 1965. Its ecologists research invasive species, track blue crabs and other vital fisheries, study harmful chemicals and uncover the impacts of climate change. Today it houses some of the longest-running environmental field studies in the world. For more information, visit http://www.
NOTE TO EDITORS: You may read other press releases from Oak Ridge National Laboratory or learn more about the lab at http://www.
Twitter - http://twitter.
RSS Feeds - http://www.
Flickr - http://www.
YouTube - http://www.
LinkedIn - http://www.
Facebook - http://www.
Ron Walli | EurekAlert!
Sun's impact on climate change quantified for first time
27.03.2017 | Schweizerischer Nationalfonds SNF
NASA examines Peru's deadly rainfall
24.03.2017 | NASA/Goddard Space Flight Center
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
27.03.2017 | Health and Medicine
27.03.2017 | Life Sciences
27.03.2017 | Earth Sciences