Biogeochemical controls of arsenic mobilization in rural Bangladesh: the role of methane and ammonium

• Applicant: Professor Dr. Frank Keppler
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 576184236

Arsenic contamination of groundwater poses a significant public health threat in many parts of the world, with Bangladesh being among the most critically affected regions. More than 40 million people are exposed to groundwater with arsenic concentrations exceeding the World Health Organization’s guideline value of 10 µg/L. Despite nearly three decades of intensive research, the underlying biogeochemical mechanisms responsible for arsenic mobilization in aquifers remain incompletely understood. A mechanistic understanding of these processes is essential for the development of effective, site-specific, and sustainable mitigation strategies. This project focuses on the biogeochemical controls of arsenic release in rural Bangladeshi aquifers, with particular emphasis on the roles of methane and ammonium as electron donors in microbially mediated iron(III) reduction, a key pathway for arsenic mobilization. Preliminary data from field sites in Bangladesh reveal elevated concentrations of methane and ammonium in groundwater, yet their mechanistic contributions to arsenic release remain unresolved. We hypothesize that microbial oxidation of methane and ammonium, coupled to the reductive dissolution of arsenic-bearing iron(III)-(hydr)oxides, represents a critical driver of arsenic mobilization at shallow to intermediate depths. We further propose that methane generation, vertical migration, and subsequent oxidation, as well as ammonium transformation, occur in spatially and temporally distinct redox zones, sustaining microbial activity that promotes arsenic release. These processes are expected to be modulated by seasonal recharge, organic matter availability, and local hydrostratigraphy. To test these hypotheses, we will perform depth-specific, multi-seasonal sampling of groundwater, gases, and sediments at two representative field sites in Bangladesh. Using state-of-the-art stable isotope techniques, alongside comprehensive geochemical, hydrological, and microbial analyses, we aim to identify the key transformation pathways of methane and ammonium and their roles in arsenic cycling. Special attention will be given to coupling microbial data with hydrogeological and geochemical observations to unravel the relevant metabolic processes. By integrating data from sediment, water, and gas phases across temporal and spatial gradients, we will construct a process-based conceptual model of arsenic mobilization, providing a scientific basis for future risk assessment and the design of effective, site-specific remediation strategies.

• DFG Programme: Research Grants
• International Connection: Bangladesh, Switzerland, United Kingdom
• Co-Investigators: Professor Dr. Olaf Bubenzer; Dr. Caroline Buchen-Tschiskale
• Cooperation Partners: Professor Dr. Kazi Matin Ahmed; Professor Dr. Moritz Felix Lehmann; Professor Dr. David Polya; Laura Richards, Ph.D.