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New insights on arsenic cycling


Arsenic is a natural element found in abundance in the Earth’s crust. Depending on the composition of minerals and rocks and environmental conditions it may be mobilized from the minerals  present in an aquifer and contaminate the groundwater. Such is the case in many regions of the world such as Bangladesh, Vietnam, Cambodia and Thailand. Most often discussed are redox reactions driving the release of arsenic from the minerals into the water and the distribution of inorganic arsenic species in the water. Water is considered safe to drink when total arsenic levels are below 10 micrograms per liter. Levels above that are considered cancer risks.

The new study:
 Photo of Qusheng Jin, associate professor in the UO Department of Geological Science

Qusheng Jin, associate professor in the
UO Department of Geological Science
Credit: University of Oregon
"Traditionally the presence of the organic form in groundwater has been ignored. The focus has always been on inorganic forms, arsenate and arsenite", said geologist Qusheng Jin, an associate professor in the UO Department of Geological Sciences. That approach, Jin said, over-simplifies the view on arsenic levels and overlooks how human activities, including pumping and irrigation, or environmental factors such as heavy rain or drought may influence organic forms.

A report on arsenic concentrations in the drinking water of the city of Creswell exceeding allowable standards in 2008 fueled the curiosity of Jin and generated "a wild hypothesis" about a bacterial process possibly being responsible for such enhanced arsenic concentration. To test the hypothesis, Jin turned from a lab-based modeler into a field researcher. He started small, with an internal UO seed grant to begin gathering water samples. Next came a grant from the National Science Foundation to test his theory.

The aquifer in Oregon's southern Willamette Valley where the research was conducted, consists of volcanic sandstone, tuff and silicic ash, overlaid by lava flows and river sediments. The basin floor dates to 33 million years ago. The fieldwork, led by Jin, involved gathering water samples at depths ranging from 20 to 40 meters (66 to 131 feet) from 23 wells located on rural properties near Creswell, Oregon.

This map shows the location of the aquifer in Oregon's southern Willamette Valley where the research was conducted. The area is south of Eugene.
Credit: Courtesy of Scott C. Maguffin    
[click to enlarge]

The organic arsenic species that caught the team's attention is dimethylarsinate (DMA). In 10 of the wells tested, DMA was found with concentrations as high as 16.5 micrograms per liter. DMA's concentration -- sometimes exceeding 10 percent of inorganic arsenic -- always correlates with the overall arsenite level, Jin said. Eventually, he added, the conversion process can turn arsenic into the volatile gas arsine.

To test the hypothesis that arsenic cycling was driven by microbial activity, UO doctoral student Scott C. Maguffin conducted a series of three laboratory experiments involving dissolved arsenite and arsenate taken from wells in the study area. The addition of ethanol in the final experiment stimulated bacterial activity and thus enhancing the conversion of inorganic arsenic via biomethylation resulting in DMA concentrations much higher than those found in the field.

"I am concerned about the impact of this cycling process in aquifers," Jin said. "If this process is as important as we believe it is, it will impact the transport and fate of arsenic in groundwater. Many organic arsenic forms are volatile and prone to diffusion. Where will these organic arsenic forms go? Will they ever make to the surface?"

The findings, Jin added, open a window on naturally occurring arsenic cycling and how, eventually, it might be manipulated to treat arsenic-contaminated water. "The cycling is important," he said. "This basic science provides a conceptual framework to understand arsenic behavior in the environment."

The results of the study have been published online March 9 in the journal Nature Geoscience.

Source: adapted from material provided by University of Oregon

The cited study:

Scott C. Maguffin, Matthew F. Kirk, Ashley R. Daigle, Stephen R. Hinkle, Qusheng Jin, Substantial contribution of biomethylation to aquifer arsenic cycling, Nature Geoscience
(2015). doi:10.1038/ngeo2383

Related studies (newest first):

Y.-G. Zhu, M. Yoshinaga, F.-J. Zhao, B.P. Rosen, Earth abides arsenic biotransformations, Annu. Rev. Earth Planet Sci., 42 (2014) 443–467. doi: 10.1146/annurev-earth-060313-054942

A. Mestrot, J. Feldmann, E.M. Krupp, Mahmud S. Hossain, G. Roman-Ross, A.A. Meharg, Field fluxes and speciation of arsines emanating from soils, Environ. Sci. Technol., 45 (2011) 1798–1804. doi: 10.1021/es103463d

X. Xie, A. Ellis, Y.X. Wang, Z.M. Xie, M.Y. Duan, C.L. Su, Geochemistry of redox-sensitive elements and sulfur isotopes in the high arsenic groundwater system of Datong Basin, China, Sci. Total Environ., 407 (2009) 3823–3835. doi: 10.1016/j.scitotenv.2009.01.041

D. Lièvremont, P.N. Bertin, M.-C. Lett, Arsenic in contaminated waters: Biogeochemical cycle, microbial metabolism and biotreatment processes, Biochimie, 91 (2009) 1229–1237. doi: 10.1016/j.biochi.2009.06.016

J. Qin, B.P. Rosen, Y. Zhang, G.J. Wang, S. Franke, C. Rensing, Arsenic detoxification and evolution of trimethylarsine gas by a microbial arsenite S-adenosylmethionine methyltransferase, Proc. Natl Acad. Sci. USA, 103 (2006) 2075–2080. doi: 10.1073/pnas.0506836103

E.D. Rhine, E. Garcia-Dominguez, C.D. Phelps, L.Y. Young,  Environmental microbes can speciate and cycle arsenic, Environ. Sci. Technol., 39 (2005) 9569–9573. doi: 10.1021/es051047t

B.J. Lafferty, R.H. Loeppert, Methyl arsenic adsorption and desorption behavior on iron oxides, Environ. Sci. Technol., 39 (2005) 2120–2127. doi: 10.1021/es048701+

F.S. Islam, A.G. Gault, C. Boothman, D.A. Polya, J.M. Charnock, D. Chatterjee, J.B. Lloyd, Role of metal-reducing bacteria in arsenic release from Bengal delta sediments, Nature, 430 (2004) 68–71. doi: 10.1038/nature02638

R.S. Oremland, J.F. Stolz, The ecology of arsenic, Science, 300 (2003) 939–944. doi: 10.1126/science.1081903

R. Mukhopadhyay, B.P. Rosen, L.T. Phung, S. Silver, Microbial arsenic: From geocycles to genes and enzymes, FEMS Microbiol. Rev.,  26 (2002) 311–325. doi: 10.1016/S0168-6445(02)00112-2

R. Bentley, T.G. Chasteen, Microbial methylation of metalloids: Arsenic, antimony, and bismuth, Microbiol. Mol. Biol. Rev., 66 (2002) 250–271. doi: 10.1128/MMBR.66.2.250-271.2002

A. Shraim, N.C. Sekaran, C.D. Anuradha, S. Hirano, Speciation of arsenic in tube-well water samples collected from West Bengal, India, by high-performance liquid chromatography–inductively coupled plasma mass spectrometry, Appl. Organomet. Chem., 16 (2002) 202–209. doi: 10.1002/aoc.279

N.F. Lin, J. Tang, J.M. Bian, Characteristics of environmental geochemistry in the arseniasis area of the Inner Mongolia of China, Environ. Geochem. Health, 24 (2002) 249–259. doi: 10.1007/A:1016079216654

P.L. Smedley, D.G. Kinniburgh, A review of the source, behaviour and distribution of arsenic in natural waters, Appl. Geochem., 17 (2002) 517–568. doi: 10.1016/S0883-2927(02)00018-5

Y. Sohrin, M. Matsui, M. Kawashima, M. Hojo, H. Hasegawa,  Arsenic biogeochemistry affected by eutrophication in Lake Biwa, Japan, Environ. Sci. Technol., 31 (1997) 2712–2720. doi: 10.1021/es960846w

A.C. Aurilio, R.P. Mason, H.F. Hemond, Speciation and fate of arsenic in three lakes of the Aberjona Watershed, Environ. Sci. Technol., 28 (1994) 577–585. doi: 10.1021/es00053a008

J.M. Wood, Biological cycles for toxic elements in the environment, Science 183 (1974) 1049–1052. doi: 10.1126/science.183.4129.1049

R.S. Braman, C.C. Foreback, Methylated forms of arsenic in the environment, Science, 182 (1973) 1247–1249. doi: 10.1126/science.182.4118.1247         

Related information:

Jin faculty page: http://geology.uoregon.edu/profile/qjin/
About Maguffin: http://geology.uoregon.edu/profile/maguffin/
UO Department of Geological Sciences: http://geology.uoregon.edu/
British geological survey: Arsenic contamination of groundwater
National Resources Defense Council: Arsenic in drinking water
USEPA: Arsenic in drinking water
USGS: Arsenic in groundwater of the United States
Water Management Association of Ohio: Arsenic in Ohio groundwater
WHO: Arsenic in drinking water

Related EVISA Resources

Brief summary: ICP-MS: A versatile detection system for speciation analysis
Link database: Toxicity of arsenic species
Link database: Environmental cycling of arsenic

Related EVISA News

last time modified: March 13, 2015


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