Sub-surface Biogeochemical Characteristics and Its Effect on Arsenic Cycling in the Holocene Gray Sand Aquifers of the Lower Bengal Basin

Abstract

High arsenic (As) content in the fertile delta plains of West Bengal has been widely reported since the 1990s. The shallow gray sand aquifers (GSA) deposited during the Holocene, are more commonly used as potable water sources, but they have high As levels. The release of As into groundwater is influenced by indigenous microbial communities metabolizing different organic carbon sources present in the GSA sediments. After pre-screening the groundwater for assessing their microbial phylogenetic diversity, two 50-m deep boreholes were drilled in the GSAs, and 19 sediment samples were recovered from each core. In each of these samples, grain-size distribution, sequential extraction, and quantification of trace metals and total extractable lipids were analyzed. The aquifer sediments consisted of medium to fine micaceous sand with clay lenses in between them; a thick clay layer occurred on top of both boreholes. Arsenic concentration in these sediments varied from 1.80 to 41.0 mg/kg and was mostly associated with the oxide and silicate-rich crystalline minerals. Arsenic showed a significant correlation with Fe in all fractions, suggesting the presence of Fe-(oxy)-hydroxides bound As minerals. The diagnostic lipid biomarkers showed presence of compounds derived from higher plants (epicuticular waxes) and microbial inputs. The biomarkers were abundant in clay and silt-rich layers. The samples indicated preferential preservation of n-alkanes over other functional compounds (e.g., alcohols and fatty acids), that are more reactive, and hence subject to further degradation. Sediments recovered from the borehole indicated the presence of Eustigmatophytes and vascular plant waxes that are mostly surface-derived. The sedimentary lipids also indicated the presence of complex petroleum-derived hydrocarbons. These compounds provide organic substrates, and support the preferential survival of specific microbial communities in these sediments.

Geogenic Arsenic and Microbial Contamination in Drinking Water Sources: Exposure Risks to the Coastal Population in Bangladesh

“…Linear relationship of different parameters, such as As, Fe, and EC, could be attributed to natural activity, and the interrelationship of TC, E. coli, and FC could be attributed to biological activity. In the coastal Bangladesh (Bengal basin), As showed a significant correlation with Fe (Ghosh et al, 2017). In a recent study, Chidambaram et al (2018) mentioned that association of Fe with other elements is the major controlling factor of groundwater chemistry in the coastal area of Bangladesh and India (West Bengal).…”

“…Therefore, providing a solution for safe and drinkable groundwater in Bangladesh is an environmental health issue of the highest priority (Bhattacharya et al, 1997). In several Asian countries, including Bangladesh and West Bengal (an adjacent Indian state), toxic elemental (e.g., As) concentration in groundwater and its impact on human health has been widely researched (Bhattacharya et al, 2002;Yu et al, 2003;van Geen et al, 2008;Das et al, 2009;Shrivastava et al, 2014;Ghosh et al, 2017), and it is considered the largest and most important societal and environmental problem in this region of the world at the current time (Kapaj et al, 2006).…”

Coping with arsenic stress: Adaptations of arsenite‐oxidizing bacterial membrane lipids to increasing arsenic levels

“…This indicates congruence between the uncultured‐ and culture‐dependent approaches. The Burkholderial genera Acidovorax and Hydrogenophaga indicated predominance over all the arsenite‐oxidizing groups in many different BDP aquifers (Ghosh et al., , ; Ghosh, Routh, & Bhadury, 2015; Ghosh, Routh, Dario, et al., 2015); Heinrich‐Salmeron et al., ; Sultana et al., ). These two bacteria participate in oxidation/reduction reactions involved in Fe cycling colinked to As biogeochemical cycling (Ghosh et al., ; Meyer‐Dombard, Amend, & Osburn,).…”

“…Many theories have been proposed to understand the mechanism of As release into groundwater (Bhattacharya, Chatterjee, & Jacks, ; Harvey et al., ; McArthur et al., ; Nickson et al., ), of which the microbial transformation pathway is most widely accepted. Microorganisms play an important role in the biogeochemical cycling of As and its release into the aquifer (Ghosh, Routh, & Bhadury, 2015, ; Ghosh, Routh, Dario, & Bhadury, 2015; Sultana, Härtig, Friedrich, Seiferta, & Schlömanna, ). This can occur through microbial reduction in As‐bearing Fe(III) minerals as electron sources (Bhattacharya et al., ; Cummings, Caccavo, Fendorf, & Rosenzweig,; Nickson, McArthur, Ravenscroft, Burgess, & Ahmed, ; Nickson et al., ; van Geen et al., ) or using arsenate [As(V)] as an electron acceptor (Zobrist, Dowdle, Davis, & Oremland, ; Oremland & Stolz, ; Lloyd &Oremland, ), after reducing Fe(III) (Islam et al., ).…”

“…To the best of our knowledge this is the first study in which membrane‐bound PLFAs of indigenous bacteria isolated from the BDP aquifers have been characterized in response to increasing As(III) concentration in the cultures. The data provide an opportunity to understand complex biogeochemical interactions between bacterial communities and As cycling in these groundwater (Ghosh, Routh, & Bhadury, 2015, ).…”