Major and trace (including arsenic) groundwater chemistry in central and southern Myanmar
Gianfranco P. Pincetti-Zúniga, Laura A. Richards, Yin Min Tun, Hla Phone Aung, Aung Kyaw Swar, U. Phyar Reh, Thet Khaing, Moe Moe Hlaing, Tin Aung Myint, Myat Lay Nwe, David A. Polya
Abstract
Myanmar, in Southeast Asia, is categorized as a Least Developed Country, facing substantial challenges towards meeting 2030 Sustainable Development Goal targets, including ensuring access to safe water and sanitation. The occurrence of geogenic contaminants, notably arsenic, in Myanmar groundwaters is relatively poorly understood, particularly as compared to other countries in South/Southeast Asia. Improving the understanding of groundwater quality in Myanmar is hence a major concern and relevant to the health of millions of local inhabitants who extensively use groundwater. A groundwater survey was undertaken at 85 sites across five distinctly contrasting zones within three of Myanmar's main river basins (Chindwin-Ayeyarwady, Sittaung, and Salween) to assess the occurrence of arsenic and other potentially harmful elements, and to study the dominant geochemical controls in each zone/basin. A significant number of samples were affected by water quality issues, based on World Health Organization (WHO) guidelines, including elevated arsenic (>10 μg.L−1) in 14% of all samples within the basins studied. Fluoride, nitrate, salinity, iron, manganese, and aluminum also exceeded WHO drinking water guidelines in some locations. Arsenic typically occurred as inorganic AsIII and largely arose from the reductive dissolution of Fe(Mn)-(hydro)xides and was broadly associated with relatively high HCO3 and NH4. Variable dominant geochemical controls on groundwater composition were identified, notably (i) calcite and dolomite dissolution in the Salween basin; (ii) cation exchange, carbonate dissolution and saline intrusion in the Ayeyarwady delta; and (iii) gypsum dissolution, silicate weathering, and cation exchange in Chindwin-Middle Ayeyarwady. This reconnaissance study provides new information on groundwater composition and corresponding geochemical controls across contrasting, and previously underrepresented, areas of Myanmar and may help to inform further hazard assessment, monitoring and/or mitigation strategies.