Abstract
Arsenic concentrations in groundwater extracted from quaternary alluvial sediments pose a serious health issue for inhabitants living in several countries in Southeast Asia. A widely approved hypothesis states that reductive dissolution of Fe-bearing minerals releases As oxyanions to ground water and the original source of As has to be located in mafic rocks occurring across the entire Himalayan belt. Yet, recent trace element analyses of ground water from the lowlands (Terai) of Nepal show a clear decoupling of As and Fe. The positive correlation of K, Na, and trace elements like Li, B, and Mo with arsenic points out to clay minerals hosting the toxic element. This pattern of trace elements found in the ground water of the Terai also advocates against an original source of As in mafic rocks. The lithophile elements like Li, B, P, Br, Sr, and U reflect trace element composition typical for felsic rocks as an origin of As. All the mentioned elements are components of clay minerals found ubiquitously in some of the most characteristic felsic rocks of the Nepal Himalaya: metapelites and leucogranites—all these rocks exhibiting a high abundance of especially B, P, and As besides Cd and Pb.
Highlights
Arsenic concentrations found in the groundwater in quaternary alluvial sediments in the lowland Terai region of Nepal and other countries of South Asia (Bangladesh, India, Nepal, Myanmar, China, Vietnam, Cambodia, and China) often exceed the World Health Organization (WHO) drinking water guideline (10 μg/L)
A second field campaign was arranged in pre-monsoon time (April 2017) in order to detect for differences in arsenic concentration in groundwater between the two seasons
Even though in [34] it is reported about a positive dependence of As on Fe in West Bengal and in [35] a positive correlation between As and Fe (r = 0.77) in the aquifer of the Nawalparasi district is mentioned, a decoupling between aqueous As and Fe has been observed in [13–15]
Summary
Arsenic concentrations found in the groundwater in quaternary alluvial sediments in the lowland Terai region of Nepal and other countries of South Asia (Bangladesh, India, Nepal, Myanmar, China, Vietnam, Cambodia, and China) often exceed the World Health Organization (WHO) drinking water guideline (10 μg/L). The origin of the arsenic contamination is clearly geogenic, and its elevated concentrations in natural ground waters are considered to be due to natural weathering of the Himalayan belt [4–9] These quaternary alluvial sediments are carried by the Ganga-Brahmaputra river system and build up the Himalayan foreland basin and the Bengal fan—one of the largest modern fluvial deltas of the world [10, 11]. As there is no correlation found between As and Fe concentrations in groundwater in the Terai of Nepal, an obvious correlation between lithophile element concentration and As the initial source rocks is of felsic and not mafic composition.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
