Major Factors Controlling Arsenic Occurrence in the Groundwater and Sediments of the Chianan Coastal Plain, SW Taiwan

Abstract

). The different combination of As, Fe, and SO 4 2-concentrations of groundwater reflect various redox potentials. The reductive dissolution of As-rich Fe-(hydr)oxides is believed to be the major source of As in the groundwater, but the contents of SO 4 2-, humic substances and residence time of water are also responsible for the variation of dissolved As in the Chianan coastal plain.

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

“…The high concentration of As(III) species present in these waters reflects the reduced environment of the aquifer, which may be caused by the low oxygen fugacity or the presence of other reducing agents, or both, in the groundwater system. Arsenic in groundwater of Chianan plain is present largely as As(III) Chen and Liu 2007). The low MMA and DMA concentrations (below detection limit \1 lg/l) found in the well waters of the Budai area suggest that other more complicated organoarsenicals are probably not present in significant amounts in the well water.…”

The binding nature of humic substances with arsenic in alluvial aquifers of Chianan Plain, southwestern Taiwan

“…The Chianan Plain is bounded on the east by the western edge of the Western Foothills, which is mostly composed of siltstone and fine-grained sandstone of the late Tertiary epoch and provides the source rocks for the Chianan Plain. Accordingly, the upper-most 300 m of which is mostly silt and clay, intercalated with thin lenticular fine-sand layers (Chen and Liu, 2007); these sediments were deposited in mixed sedimentary environments, including lagoon, estuarine, shallow marine and fluvial plains during late Pleistocene and Holocene. The average rate of sediment accumulation during Holocene reached a high value of~1 cm/yr in the coastal areas as determined by radiocarbon dating (Liu et al, 1997).…”

“…Hydrogeological characteristics are consistent with the very low permeability shown in pumping tests and the occurrence of saline water in the aquifers deposited in a marine environment. Chen and Liu (2007) interpreted the high chlorinity for some wells in aquifer (I) as being due to strong evaporation in the coastal zone 2. Methodology…”

Origin of methane in high-arsenic groundwater of Taiwan – Evidence from stable isotope analyses and radiocarbon dating

“…Accordingly, the upper-most $300 m of which is mostly silt and clay, intercalated with thin lenticular fine-sand layers ( Fig. 2a; Chen and Liu, 2007); these sediments were deposited in mixed sedimentary environments, including lagoon, estuarine, shallow marine, and fluvial plains during late Pleistocene and Holocene. The average rate of sediment accumulation during Holocene reached a high value of $1 cm/yr in the coastal areas as determined by radiocarbon dating (Liu et al, 1997).…”

“…1). These groundwaters are also characterized by high concentrations of dissolved humic substances and arsenic (Chen and Liu, 2007), both of which were considered to be responsible for endemic ''blackfoot disease" through drinking of groundwater (Tseng et al, 1961;Lu, 1990). It has long been recognized that occurrence of CH 4 generally implies a considerably reducing state in the geochemical environment (Stumm and Morgan, 1996).…”