Geochemical Evaluation of Arsenic and Manganese in Shallow Groundwater and Core Sediment in Singair Upazila, Central Bangladesh

Geochemical characteristics of shallow groundwaters and core sediments are studied to better understand the sources and transportation process responsible for As and Mn enrichment in Singair Upazila of Manikgonj District in Bangladesh. Results demonstrate that the groundwater is mostly of Ca-HCO₃ and Ca-Mg-HCO₃ types. Concentrations of As in groundwater ranged from 1 to 159 μg/L, with about 59% of these exceeded the WHO drinking water guideline of 10 mg/L. In addition, all groundwater samples had higher concentrations of Mn (0.6-5.7 mg/L) and Fe (0.9-16.5 mg/L) than the WHO drinking water guidelines (0.4 and 0.3 μg/L, respectively). Most groundwaters contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V). High concentration of As (23 mg/kg) with elevated levels of FeO, MnO and TOC were found within the upper 15 m of silty clay sediments. Multivariate geostatistical analysis showed that dissolution of the Fe-Mn oxides was the dominant process of As and Mn release in groundwater. Geochemical modeling suggested that the concentrations of As, Mn, Fe and PO₄^3- in groundwaters were also influenced by secondary minerals phases in addition to redox processes.