Arsenic mobilization into groundwater caused by microbial iron(III) mineral reduction coupled to methane oxidation in the Red River delta in Vietnam

• Applicants: Professor Dr. Andreas Kappler; Professorin Sara Kleindienst, Ph.D.
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Mineralogy, Petrology and Geochemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540514573

Geogenic arsenic (As) contamination is a pervasive issue in many aquifers in southeast Asia, posing a significant threat to the health of millions of people. Understanding mechanisms controlling As mobilization into groundwater is crucial but is oftentimes limited due to the complex mineralogical, geochemical and hydrological conditions. The reductive microbial dissolution of As-bearing iron (Fe) (III) (oxyhydr)oxide minerals, coupled to the oxidation of natural organic matter (NOM), is a widely accepted mechanism for As mobilization into groundwater. In the last years, elevated dissolved methane (CH4) concentrations have been detected in various As-contaminated aquifers, and dissolved As strongly correlated with CH4 and Fe(II) in groundwater. These findings raise questions about whether CH4 can serve as an electron donor (instead of NOM) for microbial reduction of As-bearing Fe(III) (oxyhydr)oxide minerals. Investigations conducted as part of our previous, DFG-funded project "AdvectAs" have provided first evidence on the link between Fe(III)-dependent anaerobic oxidation of CH4 (AOM) and As mobilization in the Red River Delta (Vietnam). Nonetheless, several critical questions remained unanswered: i) To which extent does Fe(III)-dependent AOM contribute to As mobilization in different locations along the Red River Delta? ii) Which are the predominant metabolic pathways and active microbial communities present in aquifers where Fe(III)-dependent AOM is observed? iii) What is the identity of and can we isolate the microorganisms responsible for Fe(III)-dependent AOM? iv) What are the identity of the genes and metabolic pathways associated with Fe(III)-dependent AOM in (pure or enrichment) cultures? Hence, the primary objective of this project is to investigate the role of Fe(III)-dependent AOM for As mobilization within the Red River Delta. To accomplish this, we will employ biogeochemistry tools and biomolecular analysis (including omics). The project is organized into six work packages (WPs). Field campaigns will be conducted in WPs 1 and 4 for sample collection, followed by the characterization of geochemical parameters and microbial communities in groundwater and sediments. WPs 2 and 5 will focus on isolating Fe(III)-dependent AOM microorganisms, characterizing their substrate profiles, and elucidating the metabolic pathways and gene expression profiles of (pure or enrichment) cultures. WPs 3 and 6 will quantify the rates of CH4 oxidation under various geochemical conditions and perform metagenomic (and, if feasible, metatranscriptomic) analyses on selected sediment samples to identify the dominant and active metabolic pathways influencing As mobilization at the field sites. We anticipate that the outcomes of this project will elucidate the significance of Fe(III)-dependent AOM leading to As mobilization and contribute to our understanding of the global methane sink by Fe(III)-dependent AOM microorganisms.

• DFG Programme: Research Grants