Publication Date:
2008-07-25
Description:
Tens of millions of people in south and southeast Asia routinely consume ground water that has unsafe arsenic levels. Arsenic is naturally derived from eroded Himalayan sediments, and is believed to enter solution following reductive release from solid phases under anaerobic conditions. However, the processes governing aqueous concentrations and locations of arsenic release to pore water remain unresolved, limiting our ability to predict arsenic concentrations spatially (between wells) and temporally (future concentrations) and to assess the impact of human activities on the arsenic problem. This uncertainty is partly attributed to a poor understanding of groundwater flow paths altered by extensive irrigation pumping in the Ganges-Brahmaputra delta, where most research has focused. Here, using hydrologic and (bio)geochemical measurements, we show that on the minimally disturbed Mekong delta of Cambodia, arsenic is released from near-surface, river-derived sediments and transported, on a centennial timescale, through the underlying aquifer back to the river. Owing to similarities in geologic deposition, aquifer source rock and regional hydrologic gradients, our results represent a model for understanding pre-disturbance conditions for other major deltas in Asia. Furthermore, the observation of strong hydrologic influence on arsenic behaviour indicates that release and transport of arsenic are sensitive to continuing and impending anthropogenic disturbances. In particular, groundwater pumping for irrigation, changes in agricultural practices, sediment excavation, levee construction and upstream dam installations will alter the hydraulic regime and/or arsenic source material and, by extension, influence groundwater arsenic concentrations and the future of this health problem.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Polizzotto, Matthew L -- Kocar, Benjamin D -- Benner, Shawn G -- Sampson, Michael -- Fendorf, Scott -- England -- Nature. 2008 Jul 24;454(7203):505-8. doi: 10.1038/nature07093.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth Sciences, Stanford University, Stanford, California 94305, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18650922" target="_blank"〉PubMed〈/a〉
Keywords:
Arsenic/*analysis
;
Arsenic Poisoning/epidemiology
;
Asia/epidemiology
;
Environmental Monitoring
;
Epidemiological Monitoring
;
Fresh Water/*chemistry
;
Geologic Sediments/*chemistry
;
Humans
;
Rivers/chemistry
;
*Water Movements
;
Water Pollutants, Chemical/*analysis
;
Water Supply/*analysis
;
*Wetlands
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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