Hydrochemical evolution and arsenic release in shallow aquifer in the Titas Upazila, Eastern Bangladesh
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ORIGINAL PAPER
Hydrochemical evolution and arsenic release in shallow aquifer in the Titas Upazila, Eastern Bangladesh Wael Kanoua 1,2
&
Broder Merkel 1
Received: 21 February 2017 / Accepted: 9 June 2017 # Saudi Society for Geosciences 2017
Abstract Groundwater arsenic (As) concentrations above 10 μg/L (World Health Organization; WHO standard) are frequently found in the Titas Upazila in Bangladesh. This paper evaluates the groundwater chemistry and the mechanisms of As release acting in an underground aquifer in the middlenortheast part of the Titas Upazila in Bangladesh. Previous measurements and analyses of 43 groundwater samples from the region of interest (ROI) are used. Investigation is based on major ions and important trace elements, including total As and Fe in groundwater samples from shallow (8–36 m below ground level: mbgl) and deep (85–295 mbgl) tube wells in the aforementioned ROI. Principal hydrochemical facies are Ca– HCO3, with circumneutral pH. The different redox-sensitive constituents (e.g., As, Fe, Mn, NH4, and SO4) indicate overlapping redox zones, leading to differences regarding the redox equilibrium. Multivariate statistical analysis (factor analysis) was applied to reduce 20 chemical variables to four factors but still explain 81% of the total variance. The component loadings give hints as to the natural processes in the shallow aquifers, in which organic matter is a key reactant. The observed chemistry of As, Fe, and Mn can be explained by simultaneous equilibrium between Fe-oxide and SO4 reduction and an equilibrium of rhodochrosite precipitation/dissolution. A correlation test indicates the likeliness of As release * Wael Kanoua [email protected] Broder Merkel [email protected] 1
Department of Hydrogeology, TU Bergakademie Freiberg, Gustav-Zeuner Str. 12, 09599, Freiberg, Germany
2
Department of Petroleum Engineering, Chemical and Petroleum Engineering Faculty, AL Baath University, Homs, Syria
by the reductive dissolution of Fe-oxides driven by the degradation of sediments organic matter. Other mechanisms could play a role in As release, albeit to a lesser extent. Reactive transport modeling using PHREEQC reproduced the observed chemistry evolution using simultaneous equilibrium between Fe-oxide and SO4 reduction and the equilibrium of rhodochrosite dissolution/precipitation alongside organic matter oxidation. Keywords Arsenic . Groundwater evolution . Factor analysis . Reactive transport modeling
Introduction Millions of people worldwide are exposed to high levels of the metalloid As in groundwater and through food intake; therefore, it is considered an international problem in many countries (Bundschuh et al. 2010). Many serious health issues, such as melanosis, hyperkeratosis, skin cancer, restrictive lung disease, peripheral vascular disease, and gangrene, are attributed to long-term intake of As through potable water and food ingestion at certain concentrations (Buschmann et al. 2008; Rahman et al. 2009; Rasool et al. 2016). Bangladesh is one of the most serio
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