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1. Mass fluxes of dissolved arsenic discharging to the Meghna River are sufficient to account for the mass of arsenic in riverbank sediments - Data

   https://doi.org/10.4211/hs.48e779d1aeac49609e3077625092e31b  

   Knappett, Peter; Huang, Yibin; Berube, Michelle; Datta, Saugata; Cardenas, M; Rhodes, Kim; Dimova, Natasha; Choudhury, Imtiaz; Ahmed, Kazi; van_Geen, Alexander (May 2024, HydroShare)

   This is the data used to create the published study of the same name published in the Journal of Hydrology in 2022 (10.1016/j.jconhyd.2022.104068). Shallow (<30 m) reducing groundwater commonly contains abundant dissolved arsenic (As) in Bangladesh. We hypothesize that dissolved As in iron (Fe)-rich groundwater discharging to rivers is trapped onto Fe(III)-oxyhydroxides which precipitate in shallow riverbank sediments under the influence of tidal fluctuations. Therefore, the goal of this study is to compare the calculated mass of sediment-bound As that would be sequestered from dissolved groundwater As that discharges through riverbanks of the Meghna River to the observed mass of As trapped within riverbank sediments. To calculate groundwater discharge, a Boussinesq aquifer analytical groundwater flow model was developed and constrained by cyclical seasonal fluctuations in hydraulic heads and river stages observed at three sites along a 13 km reach in central Bangladesh. At all sites, groundwater discharges to the river year-round but most of it passes through an intertidal zone created by ocean tides propagating upstream from the Bay of Bengal in the dry season. The annualized groundwater discharge per unit width at the three sites ranges from 173 to 891 m2/yr (average 540 m2/yr). Assuming that riverbanks have been stable since the Brahmaputra River avulsed far away from this area 200 years ago and dissolved As is completely trapped within riverbank sediments, the mass of accumulated sediment As can be calculated by multiplying groundwater discharge by ambient aquifer As concentrations measured in 1969 wells. Across all sites, the range of calculated sediment As concentrations in the riverbank is 78–849 mg/kg, which is higher than the observed concentrations (17–599 mg/kg). This discovery supports the hypothesis that the dissolved As in groundwater discharge to the river is sufficient to account for the observed buried deposits of As along riverbanks. 

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2. Inhibition of methanogenesis leads to accumulation of methylated arsenic species and enhances arsenic volatilization from rice paddy soil

   https://doi.org/10.1016/j.scitotenv.2021.151696  

   Zhang, Xuhui; Reid, Matthew C. (April 2022, Science of The Total Environment)
3. Bioremediation of arsenic-contaminated groundwater by sequestration of arsenic in biogenic pyrite

   https://doi.org/10.1016/j.apgeochem.2018.07.007  

   Saunders, James A.; Lee, Ming-Kuo; Dhakal, Prakash; Ghandehari, Shahrzad Saffari; Wilson, Ted; Billor, M. Zeki; Uddin, Ashraf (September 2018, Applied Geochemistry)
4. Introducing the ArsR-Regulated Arsenic Stimulon

   https://doi.org/10.3389/fmicb.2021.630562  

   Rawle, Rachel; Saley, Tara C.; Kang, Yoon-Suk; Wang, Qian; Walk, Seth; Bothner, Brian; McDermott, Timothy R. (March 2021, Frontiers in Microbiology)

   null (Ed.)

   The microbial ars operon encodes the primary bacterial defense response to the environmental toxicant, arsenic. An important component of this operon is the arsR gene, which encodes ArsR, a member of the family of proteins categorized as DNA-binding transcriptional repressors. As currently documented, ArsR regulates its own expression as well as other genes in the same ars operon. This study examined the roles of four ArsR proteins in the well-developed model Gram-negative bacterium Agrobacterium tumefaciens 5A. RNASeq was used to compare and characterize gene expression profiles in ± arsenite-treated cells of the wild-type strain and in four different arsR mutants. We report that ArsR-controlled transcription regulation is truly global, extending well beyond the current ars operon model, and includes both repression as well as apparent activation effects. Many cellular functions are significantly influenced, including arsenic resistance, phosphate acquisition/metabolism, sugar transport, chemotaxis, copper tolerance, iron homeostasis, and many others. While there is evidence of some regulatory overlap, each ArsR exhibits its own regulatory profile. Furthermore, evidence of a regulatory hierarchy was observed; i.e. ArsR1 represses arsR4 , ArsR4 activates arsR2 , and ArsR2 represses arsR3 . Additionally and unexpectedly, aioB (arsenite oxidase small subunit) expression was shown to be under partial positive control by ArsR2 and ArsR4. Summarizing, this study demonstrates the regulatory portfolio of arsenite-activated ArsR proteins and includes essentially all major cellular functions. The broad bandwidth of arsenic effects on microbial metabolism assists in explaining and understanding the full impact of arsenic in natural ecosystems, including the mammalian gut. 

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5. Arsenic and the gastrointestinal tract microbiome

   https://doi.org/10.1111/1758-2229.12814  

   McDermott, Timothy_R; Stolz, John_F; Oremland, Ronald_S (January 2020, Environmental Microbiology Reports)

   Summary Arsenic is a toxin, ranking first on the Agency for Toxic Substances and Disease Registry and the Environmental Protection Agency Priority List of Hazardous Substances. Chronic exposure increases the risk of a broad range of human illnesses, most notably cancer; however, there is significant variability in arsenic‐induced disease among exposed individuals. Human genetics is a known component, but it alone cannot account for the large inter‐individual variability in the presentation of arsenicosis symptoms. Each part of the gastrointestinal tract (GIT) may be considered as a unique environment with characteristic pH, oxygen concentration, and microbiome. Given the well‐established arsenic redox transformation activities of microorganisms, it is reasonable to imagine how the GIT microbiome composition variability among individuals could play a significant role in determining the fate, mobility and toxicity of arsenic, whether inhaled or ingested. This is a relatively new field of research that would benefit from early dialogue aimed at summarizing what is known and identifying reasonable research targets and concepts. Herein, we strive to initiate this dialogue by reviewing known aspects of microbe–arsenic interactions and placing it in the context of potential for influencing host exposure and health risks. We finish by considering future experimental approaches that might be of value. 

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