Iron mineral transformations and their impact on As (im)mobilization at redox interfaces in As-contaminated aquifers

Isotopic Labeling Reveals Microbial Methane Oxidation Coupled to Fe(III) Mineral Reduction in Sediments from an As-Contaminated Aquifer

“…Fe­(III) (oxyhydr)­oxides are the main As-bearing mineral phases in many CH 4 -containing aquifers across SE Asia, including the Van Phuc aquifer . Our study shows that Fe­(III)-dependent CH 4 oxidation has the potential to be an important pathway for As mobilization in the studied area.…”

Abundant Fe(III) Oxide‐Bound Arsenic and Depleted Mn Oxides Facilitate Arsenic Enrichment in Groundwater From a Sand‐Gravel Confined Aquifer

“…The presence of pyrite was evidenced by the well‐recognized framboidal grains with a S:Fe atomic ratio close to 2 (Figure S5c in Supporting Information ). Around 0.9 wt% As was identified along with the pyrite framboids (Figure S5c in Supporting Information ), being mainly due to strong affinity of As onto pyrite (Kontny et al., 2021). Similar to the XRD result (Figure S4 in Supporting Information ), pyrite was only observed in the Group IIs sediment.…”

“…Indeed, siderite is usually the primary Fe(II) precipitate in environments where sulfate is absent or has become exhausted (Appelo & Postma, 2005). The prevalence of siderite benefits the occurrence of high‐As groundwater since it is much less efficient in sequestering groundwater As than pyrite (Gao, Jia, et al., 2020; Kontny et al., 2021). This may also explain higher dissolved H 2 S concentrations in deep groundwater than those in shallow one (Figure 2d).…”

“…The influences of hydrogeochemical factors (e.g., redox conditions, pH, and competitive anions) on groundwater As enrichment have been well documented in shallow aquifers (Naseem & McArthur, 2018; Wang et al., 2018; Zhang, Ma, et al., 2017). Sedimentological factors, such as the amount of Fe(III)/Mn oxides (Gillispie et al., 2019), reactivity (Stuckey et al., 2016; Wallis et al., 2020), purity (Masue et al., 2007), and As/Fe molar ratio (Sø, Postma, Lan, et al., 2018) of Fe(III) oxides, and secondary Fe(II) precipitation (Kontny et al., 2021), are also important in controlling As source and fate. Upon biodegradable organic matter mineralization, high abundance of Mn oxides may buffer Fe(III) oxide reduction and As release, being mainly due to a clear redox sequence between Mn oxide reduction and Fe(III) oxide reduction (Gillispie et al., 2016, 2019).…”

Long-Term Arsenic Sequestration in Biogenic Pyrite from Contaminated Groundwater: Insights from Field and Laboratory Studies

“…High exposure to the toxic metalloid causes arsenicosis, which induces skin lesions, diabetes, peripheral neuropathy, cardiovascular disease, cancers of the skin, bladder, and lungs, and a higher risk of preterm and stillborn births [1]. Considering the soluble nature of arsenic, water-rock interactions such as weathering of As-sulfide minerals present in the sediment (e.g., orpiment (As 2 S 3 ) and realgar (AsS)) and bacterial-mediated reduction of As-rich iron (Fe) and manganese (Mn) oxides commonly release arsenic into water bodies, including aquifers used for drinking water and irrigation [3][4][5][6][7]. chosen of 0.05 mg/L As established during remediation efforts in the 1990s [11,21], which is higher than the current EPA drinking water standard at 0.01 mg/L.…”