AGU Chapman Conference on Arsenic in
Groundwater of Southern Asia
Siem Reap, Cambodia
24–27 March 2009
- Alexander van Geen, Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, USA, e-mail (firstname.lastname@example.org)
- Scott Fendorf, Environmental Earth System Science, Stanford University, Stanford, California, USA, e-mail (email@example.com)
- Kazi Matin Ahmed, Department of Geology, University of Dhaka, Bangladesh, e-mail (firstname.lastname@example.org)
- Charles Harvey, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge Massachusetts, USA, e-mail (email@example.com)
- Janet Hering, Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland, e-mail (firstname.lastname@example.org)
- Jonathan Lloyd, School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, UK, e-mail (email@example.com)
- Andrew Meharg, Department of Plant and Soil Sciences, University of Aberdeen, UK, e-mail (firstname.lastname@example.org)
- Pauline Smedley, British Geological Survey, Wallingford, Oxfordshire, UK, e-mail (email@example.com)
Millions of villagers across the floodplains and deltas of southern Asia rely on shallow tubewells to avoid drinking surface water that is highly contaminated with microbial pathogens. Sadly, the elevated arsenic content of groundwater from many of these wells is frequently leading instead to a slow death from various cancers. This Chapman Conference is intended to review a decade of Earth science research on the mechanism(s) of arsenic mobilization in groundwater of southern Asia, identify those areas where a consensus has emerged and, in the case of several important open questions that remain, determine what types of experiments or studies are needed. Special emphasis will be placed on predicting the likely fate of shallow and deeper aquifers that are currently low in arsenic and therefore offer the most realistic means of remediation in the short to medium term.
Elevated concentrations of arsenic in groundwater across southern Asia slowly poison over 100 million villagers relying on inexpensive shallow tubewells. The level of exposure has caused widespread illness including deadly cancers and, significantly, hampers the mental development of children. And yet, despite the magnitude of the health threat and a decade of research by numerous teams, many of the most basic factors and processes controlling arsenic within deltaic and floodplain aquifer systems remain unresolved.
There is broad agreement that anoxia and microbial reduction of iron is a necessary condition for sustained levels of arsenic in groundwater. But, there are strongly diverging views in the scientific community regarding the origin of the organic matter that maintains deltaic and floodplain aquifers under reducing conditions. Many researchers consider that particulate organic matter deposited with aquifer sands over the course of the Holocene plays a key role, others attribute the release of arsenic to dissolved organic matter released from peat layers, and others again believe in a transient response triggered by dissolved organic matter entering shallow aquifers, which may possibly be enhanced by widespread irrigation pumping.
The ultimate source of arsenic is almost universally believed to be natural and of Himalayan source, but it has been proposed that seawater may be the ultimate source because of precipitation onto the solid phase in mangrove systems. Both the widely assumed importance of arsenic reduction for mobilization and the role of microorganisms in that process have recently been questioned by several groups. There are also significantly different views about the role of hydrology in controlling the distribution of arsenic in groundwater. This is a particularly important issue because of continued reliance on groundwater in affected countries in order to avoid microbial pathogens found in surface waters. Decreasing arsenic exposure therefore depends on being able to predict where suitable aquifers that are low in arsenic are located, whether arsenic concentrations could rise over time, and if so at what rate.
A focused Conference on this topic could significantly enhance the understanding of the problem by engaging a limited number of scientists active in the field to set their thoughts on paper and, herewith, help direct future research in the most fruitful areas.
Underlying (Bio)Geochemical Processes
- What is the relative timing of release of As and Fe?
- What are the biogeochemical processes responsible for arsenic (and iron) release?
- How important are potential back-reactions – e.g. arsenic adsorption?
- What fuels the biogeochemical process – e.g., plant- vs. animal-derived, or recent vs. ancient, organic matter?
- Are there critical nutrients limiting release of arsenic, and is there a source of these nutrients in arsenic hotspots?
- Can a detailed understanding of microbial populations help with understanding the distribution of As in groundwater?
Role of Hydrogeology and Transport
- How are groundwater arsenic concentrations affected by surface conditions – e.g. clay or sand soils; agriculture, villages, ponds or rivers?
- Is arsenic mobilized at a greater rate from certain types of sediments?
- Has the development of paddy fields significantly influenced the pattern of arsenic concentrations in groundwater?
- What will be the consequences of prolonged irrigation of rice paddies with groundwater elevated in arsenic?
Vulnerability of Low-Arsenic Aquifers – Policy Implications
- Is the age of a well since installation relevant and if so, how?
- How do arsenic concentrations respond to changes in recharge from village construction, pond construction, shifting agricultural practices?
- Does the release of organic carbon from latrines lead to arsenic enrichments in groundwater?
- How do arsenic concentrations vary with concentrations of other potentially harmful solutes, such as manganese and heavy metals?
- What simple/cheap observations might aid the targeting of low arsenic aquifers?
- Can biogeochemical processes be harnessed to remove arsenic from groundwater in situ and ex situ?
- Do we know enough about the biogeochemistry/microbial ecology of deep wells, and how they will respond to prolonged pumping?
Consensus(?) and Critical Experiments
- What are the similarities and differences between Himalaya catchments where arsenic is found (or not found) in groundwater in terms of spatial patterns, organic carbon sources, and land-use practices?
- Are there commonalities between the mechanisms of arsenic release in inland and coastal aquifers?
- Are laboratory studies to identify arsenic-mobilizing microorganisms and the functional genes that they carry useful?
- Can laboratory experiments help us understand processes in situ and inform mitigation strategies?
- Could hydrogeologic methods widely applied in the West to groundwater contamination problems (3D flow and transport modeling, 3D networks of pressure transducers, field-scale tracer tests...) be applied to understand arsenic contamination in poor countries?
- Why have these methods been applied so sparingly?
- What should we as a research community do collectively to project future groundwater levels of arsenic and evaluate long-term solutions?
The conference will take place over 4 days and will be limited to approximately 50 scientists and advanced students from within and outside the affected countries. We will actively seek representation from countries affected by groundwater arsenic. Each day of the conference will be organized around one of four broad themes listed above. On the first three mornings, speakers provisionally identified by the Program Committee will be invited to develop each theme. Two members of the Program Committee will moderate an open discussion in the afternoon on 'the theme of the day', including possibly a number of shorter additional presentations. There will be opportunity to display and examine posters throughout the conference. An important practical matter relevant to policy will be addressed on the third day: the vulnerability of aquifers that are currently low in arsenic. The last day of the meeting, moderated by the conveners, will be devoted to reaching a consensus on the key processes controlling arsenic mobilization and, where disagreement persists, the identification of key experiments that could settle certain issues.
The conveners are contacting a number of agencies and institutions concerning co-sponsorship of the conference in an effort to obtain travel support for as many participants as possible. Information on financial support for this conference will be updated on this web page as it becomes available.
If you would like to receive future updates about this conference, e-mail firstname.lastname@example.org. For information about the scientific program, please contact one of the conveners via e-mail:
Alexander van Geen
Lamont-Doherty Earth Observatory of Columbia University
Palisades, New York, USA
Environmental Earth System Science, Stanford University
Stanford, California, USA