Geochemical Characteristics of Arsenic in Groundwater of the Lanyang Plain, Taiwan: Implication to Arsenic Release Processes
Date Issued
2008
Date
2008
Author(s)
Wu, Ming-Che
Abstract
Arsenic (As) is an ubiquitous metalloid in crust of the earth. High arsenic concentrations (average 0.091 mg/L) of groundwater were found in Lanyang plain of Taiwan. Groundwater from 29 wells was sampled and 14 hydro-geochemical parameters were analyzed. Factor analysis was applied to determine major influence factors of the arsenic, and PHREEQC was used to calculate the distribution of aqueous species and saturation index of which affected groundwater quality. 403 geological core samples from 9 drilling wells were collected and analyzed the contents of total arsenic and iron. Meanwhile, 19 and 9 core samples around high arsenic concentration groundwater were selected, respectively, for additionally sequential extraction and mineralogical phases analyzes, using x-ray fluorescence (XRF), high resolution x-ray photoelectron (XPS) and scanning electron microscope and energy dispersive spectrometer (SEM-EDS). Results of the arsenic-pollution factor determined by factor analysis indicated that infiltration of the pollutants from human activities to shallow groundwater, and the reductive dissolution from iron oxyhydroxides in the deep aquifer were the main processes of arsenic release to groundwater from the sediment. Total arsenic and iron contents of the core samples were well correlated in marine sequences. Surface analyses of core sample performed by XPS shown that arsenic was adsorbed copricipitated with noncrystalline iron oxyhdroxides. After a long term burial of sediment, microbial metabolism of organic matter creates a more reducing environment, arsenic may then be gradually released from iron oxyhydroxides by reductive dissolution or desorption to aqueous phase. Reduction dissolution or desorption of As from iron oxyhdroxides is considered as the most likely release process to groundwater in the Lanyang plain.
Subjects
Arsenic
Factor analysis
Lanyang plain
Geochemical modelling
sequential extraction
X-ray fluorescence(XRF)
High resolution x-ray photoelectron spectrometer(XPS)
Scanning electron microscope and energy dispersive spectrometer(SEM-EDS)
SDGs
Type
thesis
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