A comparative study on arsenic and humic substances in alluvial aquifers of Bengal delta plain (NW Bangladesh), Chianan plain (SW Taiwan) and Lanyang plain (NE Taiwan): implication of arsenic mobilization mechanisms

Abstract

Humic substances in groundwater and aquifer sediments from the arsenicosis and Blackfoot disease (BFD) affected areas in Bangladesh (Bengal delta plain) and Taiwan (Lanyang plain and Chianan plain) were characterized using fluorescence spectrophotometry and Fourier transform infrared (FT-IR) spectroscopy. The results demonstrate that the mean concentration of As and relative intensity of fluorescent humic substances are higher in the Chianan plain groundwater than those in the Lanyang plain and Bengal delta plain groundwater. The mean As concentrations in Bengal delta plain, Chianan plain, and Lanyang plain are 50.65 μg/l (2.8-170.8 μg/l, n=20), 393 μg/l (9-704 μg/l, n=5), and 104.5 μg/l (2.51-543 μg/l, n = 6), respectively. Average concentrations and relative fluorescent intensity of humic substances in groundwater are 25.381 QSU (quinine standard unit) and 17.78 in the Bengal delta plain, 184.032 QSU and 128.41 in the Chianan plain, and 77.56 QSU and 53.43 in the Lanyang plain. Moreover, FT-IR analysis shows that the humic substances extracted from the Chianan plain groundwater contain phenolic, alkanes, aromatic ring and amine groups, which tend to form metal carbon bonds with As and other trace elements. By contrast, the spectra show that humic substances are largely absent from sediments and groundwater in the Bengal delta plain and Lanyang plain. The data suggest that the reductive dissolution of As-adsorbed Mn oxyhydroxides is the most probable mechanism for mobilization of As in the Bengal delta plain. However, in the Chianan plain and Lanyang plain, microbially mediated reductive dissolution of As-adsorbed amorphous/crystalline Fe oxyhydroxides in organic-rich sediments is the primary mechanism for releasing As to groundwater. High levels of As and humic substances possibly play a critical role in causing the unique BFD in the Chianan plain of SW Taiwan.

Characterization on arsenic sorption and mobility of the sediments of Chia-Nan Plain, where Blackfoot disease occurred

“…Geochemical studies of the Chia-Nan Plain region suggested saturation of Fe-and Mn-bearing carbonate, sulfides, and oxides in the groundwater of the region (Nath et al 2008;Reza et al 2010). Because of the difference in solubility of iron versus arsenic sulfides, precipitation of iron sulfide may remove sulfide from solution but not arsenic if precipitation rates were fast.…”

“…It may also indicate that the state of presence of Mn or Fe 2 O 3 in the sediments might be in the form of adsorbed phases on clay mineral surfaces, or as distinct phases whose particle size is within the clay mineral range. Field data collected from Chia-Nan Plain area showed poor correlation among Fe, As, and pH, and it was attributed to various biogeochemical reactions, mineral precipitation and dissolution, and saltwater intrusions that affect the chemical evolution of groundwater locally (Nath et al 2008;Reza et al 2010). However, this research showed that aquifer and aquitard materials as well as their physical and chemical properties may also need to be considered in studying As transport and retention.…”

“…Although extensive research has been conducted in the area (Chen et al 1994;Lin et al 2006;Wang et al 2007;Nath et al 2008;Reza et al 2010), the source, mobility, and transport of As in Chia-Nan Plain aquifers were still not properly identified and characterized. In addition, as the mobility of As in the environment was controlled by its association with solid phases through adsorption and coprecipitation (Blute et al 2009), it is important to study the linkage between the sediment properties of the aquifer and aquitard materials and the state of As presence in order to elucidate the transport and retention of As in Chia-Nan Plain aquifers.…”

Interrelationship of TOC, As, Fe, Mn, Al and Si in shallow alluvial aquifers in Chapai-Nawabganj, Northwestern Bangladesh: implication for potential source of organic carbon

“…8. Bands at 3,400, 2,927, 1,600, 1,590 and 1,028 cm -1 were assigned to (O-H stretching), aliphatic C-H stretching, aromatic C=C stretching, ketone and ether, respectively (Niemayer et al 1992;Miano and Senesi 1992;Reza et al 2010c). However, some differences can also be noticed.…”

Groundwater arsenic contamination and their variations on episode of drought: Ter River delta in Catalonia, Spain

“…When the sulfide oxidation is the dominant process of the passing of As to its aqueous forms, a positive correlation can be found between the concentrations of (SO 4 2− ) and (As) (Smedley and Kinniburgh 2002). In the sedimentary basins where the groundwater has a neutral pH and reducing environment associated with the presence of fresh organic matter, the geochemical environment is a determining factor for the solubility of arsenic (Selim et al 2010). The basic trigger mechanism for the dissolution of As in porewaters environments of sedimentary basins, with neutral pH and reducing geochemical environments, can be associated to reduction-related dissolution of Fe and Mn oxides minerals, which results in the migration of As(III), Fe(II) and Mn(II) into the aqueous phase where they can reach high concentrations of these elements with a positive correlation between them (Smedley and Kinniburgh 2002), while the concentrations of (SO 4 2− ) remains low (less than 1 mg/L).…”