Arsenic in the groundwaters of the Terai Plains of Nepal

What is it about?

The origin and mobility of arsenic (As) in the groundwater environment has received serious attention in recent years. Naturally occurring As has been reported in groundwaters of the Terai Alluvial Plains (TAP) ìn southern Nepal, where groundwater exploitation has increased since the 1960s. The source of As in TAP is from the aquifers where tubewells are installed and As is leached from sediments deposited primarily due to weathering of As bearing rocks and sediments in the Himalayas. During this study, we investigated and characterized the groundwater chemistry in the central part of the TAP in Nawalparasi district in southern Nepal. TAP groundwaters are near-neutral to alkaline, with predominantly reducing character with high HCO3, low SO4 and NO3 concentrations. Elevated HCO3 levels possibly result due to the oxidation of organic matter, low SO4 levels reflect sulfate reduction. Elevated NH4+ concentrations in these groundwaters suggest dissimilatory nitrate reduction in the aquifers. Total arsenic (As tot) levels in groundwater varied from 1.7 µg/L to as high as 404 µg/L with dominance of As (III) species and elevated levels of dissolved Fe and Mn. Arsenic is mobilized in groundwaters as a result of desorption of As-oxyanions adsorbed onto Fe-and Mnoxides as well as reductive dissolution of these surface reactive phases from the sediments along with release ouf as in anoxie groundwaters.

Featured Image

Why is it important?

Understanding the processes of arsenic mobilization is fundamental understanding to locate the high risk areas. This will avoid drilling of tubewells in the areas where the risks for As mobilization is high and this will also delineate areas where news tubewells could be installed..

Perspectives