Article | Published:

Arsenic release metabolically limited to permanently water-saturated soil in Mekong Delta

Nature Geoscience volume 9, pages 7076 (2016) | Download Citation


Microbial reduction of arsenic-bearing iron oxides in the deltas of South and Southeast Asia produces widespread arsenic-contaminated groundwater. Organic carbon is abundant both at the surface and within aquifers, but the source of organic carbon used by microbes in the reduction and release of arsenic has been debated, as has the wetland type and sedimentary depth where release occurs. Here we present data from fresh-sediment incubations, in situ model sediment incubations and a controlled field experiment with manipulated wetland hydrology and organic carbon inputs. We find that in the minimally disturbed Mekong Delta, arsenic release is limited to near-surface sediments of permanently saturated wetlands where both organic carbon and arsenic-bearing solids are sufficiently reactive for microbial oxidation of organic carbon and reduction of arsenic-bearing iron oxides. In contrast, within the deeper aquifer or seasonally saturated sediments, reductive dissolution of iron oxides is observed only when either more reactive exogenous forms of iron oxides or organic carbon are added, revealing a potential thermodynamic restriction to microbial metabolism. We conclude that microbial arsenic release is limited by the reactivity of arsenic-bearing iron oxides with respect to native organic carbon, but equally limited by organic carbon reactivity with respect to the native arsenic-bearing iron oxides.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    , & Arsenic Pollution: A Global Synthesis (Wiley-Blackwell, 2009).

  2. 2.

    et al. Codeposition of organic carbon and arsenic in Bengal Delta aquifers. Environ. Sci. Technol. 40, 4928–4935 (2006).

  3. 3.

    , , & Temperature dependence and coupling of iron and arsenic reduction and release during flooding of a contaminated soil. Environ. Sci. Technol. 44, 116–122 (2010).

  4. 4.

    & Thermodynamic constraints on reductive reactions influencing the biogeochemistry of arsenic in soils and sediments. Environ. Sci. Technol. 43, 4871–4877 (2009).

  5. 5.

    et al. Mobilization of arsenic and iron from Red River floodplain sediments, Vietnam. Geochim. Cosmochim. Acta 74, 3367–3381 (2010).

  6. 6.

    et al. Arsenic mobility and groundwater extraction in Bangladesh. Science 298, 1602–1606 (2002).

  7. 7.

    et al. How paleosols influence groundwater flow and arsenic pollution: a model from the Bengal Basin and its worldwide implication. Wat. Resour. Res. 44, W11411 (2008).

  8. 8.

    et al. Dissolved organic matter sources and consequences for iron and arsenic mobilization in Bangladesh aquifers. Environ. Sci. Technol. 44, 123–128 (2010).

  9. 9.

    et al. Anthropogenic influences on groundwater arsenic concentrations in Bangladesh. Nature Geosci. 3, 46–52 (2010).

  10. 10.

    et al. Do ponds cause arsenic-pollution of groundwater in the Bengal Basin? An answer from West Bengal. Environ. Sci. Technol. 42, 5156–5164 (2008).

  11. 11.

    et al. Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater. Proc. Natl Acad. Sci. USA 110, 5331–5335 (2013).

  12. 12.

    , , , & Near-surface wetland sediments as a source of arsenic release to ground water in Asia. Nature 454, 505–508 (2008).

  13. 13.

    et al. Dissolved organic matter quality in a shallow aquifer of Bangladesh: implications for arsenic mobility. Environ. Sci. Technol. 49, 10815–10824 (2015).

  14. 14.

    et al. Arsenic release from paddy soils during monsoon flooding. Nature Geosci. 3, 53–59 (2010).

  15. 15.

    et al. Arsenic in groundwater of the Red River floodplain, Vietnam: controlling geochemical processes and reactive transport modeling. Geochim. Cosmochim. Acta 71, 5054–5071 (2007).

  16. 16.

    & Degradation of natural organic matter: a thermodynamic analysis. Geochim. Cosmochim. Acta 75, 2030–2042 (2011).

  17. 17.

    et al. Groundwater flow in an arsenic-contaminated aquifer, Mekong Delta, Cambodia. Appl. Geochem. 23, 3072–3087 (2008).

  18. 18.

    Fe(III) oxide reactivity toward biological versus chemical reduction. Environ. Sci. Technol. 37, 1319–1324 (2003).

  19. 19.

    , , , & Mineralogical and morphological constraints on the reduction of Fe(III) minerals by Geobacter sulfurreducens. Geochim. Cosmochim. Acta 73, 4004–4022 (2009).

  20. 20.

    , & Solubility and dissimilatory reduction kinetics of iron(III) oxyhydroxides: a linear free energy relationship. Geochim. Cosmochim. Acta 73, 5273–5282 (2009).

  21. 21.

    , & Enriched iron(III)-reducing bacterial communities are shaped by carbon substrate and iron oxide mineralogy. Front. Microbiol. 3, 404 (2012).

  22. 22.

    & Anaerobic microbial metabolism can proceed close to thermodynamic limits. Nature 415, 454–456 (2002).

  23. 23.

    Energetics of syntrophic cooperation in methanogenic degradation. Microbiol. Mol. Biol. Rev. 61, 262–280 (1997).

  24. 24.

    & Predicting the rate of microbial respiration in geochemical environments. Geochim. Cosmochim. Acta 69, 1133–1143 (2005).

  25. 25.

    et al. Integrated biogeochemical and hydrologic processes driving arsenic release from shallow sediments to groundwaters of the Mekong Delta. Appl. Geochem. 23, 3059–3071 (2008).

  26. 26.

    , & Deciphering and predicting spatial and temporal concentrations of arsenic within the Mekong Delta aquifer. Environ. Chem. 11, 579–594 (2014).

  27. 27.

    , & Alginate as immobilization material: I. Correlation between chemical and physical properties of alginate gel beads. Biotechnol. Bioeng. 33, 79–89 (1989).

  28. 28.

    et al. Microbial ecology of arsenic-mobilizing Cambodian sediments: lithological controls uncovered by stable-isotope probing. Environ. Microbiol. 17, 1857–1869 (2015).

  29. 29.

    , , & Indigenous arsenic (V)-reducing microbial communities in redox-fluctuating near-surface sediments of the Mekong Delta. Geobiology 13, 581–587 (2015).

  30. 30.

    , & Enzymology of electron transport: energy generation with geochemical consequences. Rev. Mineral. Geochem. 59, 27–52 (2005).

  31. 31.

    et al. A hydrogen-based subsurface microbial community dominated by methanogens. Nature 415, 312–315 (2002).

  32. 32.

    & Redox zonation: equilibrium constraints on the Fe(III)/SO4− reduction interface. Geochim. Cosmochim. Acta 60, 3169–3175 (1996).

  33. 33.

    , , & Thermodynamic control on hydrogen concentrations in anoxic sediments. Geochim. Cosmochim. Acta 62, 1745–1756 (1998).

  34. 34.

    et al. Spatial distribution and temporal variability of arsenic in irrigated rice fields in Bangladesh. 2. Paddy soil. Environ. Sci. Technol. 41, 5967–5972 (2007).

  35. 35.

    et al. Peat formation concentrates arsenic within sediment deposits of the Mekong Delta. Geochim. Cosmochim. Acta 149, 190–205 (2015).

  36. 36.

    , , & Reactivity and speciation of mineral-associated arsenic in seasonal and permanent wetlands of the Mekong Delta. Geochim. Cosmochim. Acta 171, 143–155 (2015).

  37. 37.

    & in Proceedings of the Third International Conference on Arsenic Exposure and Health Effects. Society for Environmental Geochemistry and Health (Soc. Environ. Geochem. Health, 1998).

  38. 38.

    , & Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum: iron hydroxides. Environ. Sci. Technol. 41, 837–842 (2007).

  39. 39.

    , & Alteration of ferrihydrite reductive dissolution and transformation by adsorbed As and structural Al: implications for As retention. Geochim. Cosmochim. Acta 75, 870–886 (2011).

  40. 40.

    , , & Reductive processes controlling arsenic retention: revealing the relative importance of iron and arsenic reduction. Environ. Sci. Technol. 42, 8283–8289 (2008).

  41. 41.

    & in Methods of Soil Analysis (ed. Bigham, J. M.) 639–664 (Soil Science Society of America, 1996).

  42. 42.

    , , & Probing reactivity of dissolved organic matter for disinfection by-product formation using XAD-8 resin adsorption and ultrafiltration fractionation. Water Res. 36, 3834–3848 (2002).

Download references


This work was financially supported by a US EPA STAR Graduate Fellowship awarded to J.W.S., the Stanford Woods Institute for the Environment, and a National Science Foundation Graduate Research Fellowship Program Grant no. DGE-114747 awarded to M.V.S. Portions of this work were also supported by the National Science Foundation (grant number EAR-0952019), the Stanford NSF Environmental Molecular Science Institute (NSF-CHE-0431425), the EVP programme of Stanford’s Woods Institute, and by the US Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem programme (award number DE-FG02-13ER65542). We are indebted to the staff at Resource Development International for logistical and field support, including A. Shantz, T. Makara, K. Dina and P. Nuon. We are grateful to G. Li for laboratory assistance and statistical consultation, D. Turner and M. Keiluweit for laboratory assistance, and A. Adelson, K. Boye and J. Dittmar for help with fieldwork. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.

Author information


  1. Department of Earth System Science, Stanford University, Stanford, California 94305, USA

    • Jason W. Stuckey
    • , Michael V. Schaefer
    • , Benjamin D. Kocar
    •  & Scott Fendorf
  2. Parsons Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Benjamin D. Kocar
  3. Department of Geosciences, Boise State University, Boise, Idaho 83725, USA

    • Shawn G. Benner


  1. Search for Jason W. Stuckey in:

  2. Search for Michael V. Schaefer in:

  3. Search for Benjamin D. Kocar in:

  4. Search for Shawn G. Benner in:

  5. Search for Scott Fendorf in:


S.F., J.W.S. and B.D.K. conceived the experiments, which were carried out by J.W.S., M.V.S. and B.D.K.; S.F., B.D.K., J.W.S. and S.G.B. performed site selection, and M.V.S. provided logistical support; J.W.S. performed data analyses; J.W.S., S.F. and S.G.B. performed data interpretation and co-wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Scott Fendorf.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Information

About this article

Publication history





Further reading

Newsletter Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing