Characterizing Redox Processes of Arsenic Affected Aquifers in South and Southeast Asia

In areas of South and Southeast Asia, efforts from government initiatives and aid groups have transitioned their potable water supply from surface water to groundwater. As this diminishes health concerns stemming from bacterial pathogens found in unsafe surface water, drinking water pumped from tube wells that reach subsurface aquifers has been identified as having copious, yet varying levels of naturally occurring arsenic. Arsenic (As) poisoning currently poses an immense threat towards human health in the area, predominantly in Bangladesh, where more than 3 million tube wells span the country, and millions more exist in surrounding regions. The As is naturally occurring and is released due to reducing conditions within the aquifers. The geochemical processes taking place within potable aquifers can allow for unwanted compounds that not only lead to current human health problems and fatalities, but also pose issues with supplying safe drinking water in the future. While concentrations are notably high throughout South and Southeast Asia, a wide degree of spatial variability exists with concentrations varying between safe low-As to unsafe high-As over a range of spatial scales. Given these varying concentrations, a better characterization of redox processes is needed to identify specific reduction and oxidation trends and other significant relationships between As and common chemical compounds.  Here, I bring together data from many previously published datasets for aquifers of South and Southeast Asia and perform a redox characterization to more than 2000 samples in order to analyze redox trends that can lead to the mobilization of naturally occurring As in these aquifers. By compiling and analyzing these datasets together I have developed a thorough redox characterization that has never been accomplished on the recorded samples and which improves our overall understanding of the dominant geochemical processes throughout the region.  Furthermore, I use my redox characterization to improve our mechanistic understanding of the drivers of variability of As within groundwater. Identifying the redox processes and trends that can lead to As occurrence is vital to the safety of the people in South and Southeast Asia. This study can also provide a basis for identifying areas that may be vulnerable to As exposure and can improve our understanding of how groundwater evolves through natural and anthropogenic processes.