Host: The Association of Japanese Geographers
The arsenic distribution in aquifers is mainly restricted within the Holocene alluvial plain, the lowland Terai. Hot spot locates very randomly but probably according to the local geology with the lateral and vertical variability, such as sedimentary facies, remains of former meandering, north-dipping thrusts, and multiple folds.
In order to identify the source of arsenic we investigated water quality and geology in four areas in Nepal, Mountain, Hill, Siwalik, and Terai. The metamorphic rocks of the Himalayas will least contribute arsenic contaminations in Terai because they are crystalline mainly consisting of feldspar, quartz and marble. However, weathered marine sediments with fluvial and fluvio-glacial deposits are identified in Jomsom (Annapurna Mountain area) where arsenic rich minerals including arsenopyrite (FeAsS) and arsenic trioxide (As2O3) are generally considered to have been eroded and transported by Kali Gandaki River. Arsenic bearing minerals were deposited at the specific beds in Terai during early-mid Holocene sea level rise.
Arsenic is mobilized in local groundwater with the alkaline nature and can be easily removed and adsorbed in aquifer sediments influenced by pH and redox conditions and by iron related geochemistry. By our study positive correlations have been confirmed among the total concentrations of boron and Fe with arsenic in the groundwater of Parasi in Terai.
