Arsenic in groundwater in the southern lowlands of Nepal and its mitigation options: a review

Abstract

As in several other countries of Southeast Asia (namely Bangladesh, India, Myanmar, China, Vietnam, and Cambodia) arsenic (As) concentrations in the groundwater of the lowlands of Nepal (the so called Terai) can reach concentrations that are unsafe to humans using the groundwater as drinking water. Whereas Bangladesh has received much international attention concerning the As crisis, Nepal was more or less neglected. The first report about As contamination of the groundwater above toxic levels in Nepal was published in 1999. Twenty-four percent of samples analyzed (n = 18 635) from the Terai Basin exceeded the WHO guideline of 10 μg/L. Since the first overall survey from 2001, only sporadic information on the situation has been published. The geological and geochemical conditions favour the release of the contaminant as As can be easily solubilized in groundwaters depending on pH, redox conditions, temperature, and solution composition. The thin alluvial aquifers of the Terai are some of the most severely As contaminated. These sediments constituting a hugh proportion of the Terai aquifers are derived from two main sources: (i) sediments deposited by large rivers that erode the upper Himalayan crystalline rocks, and (ii) weathered meta-sediments carried by smaller rivers originating in the Siwalik forehills. The generally low redox potential and low SO42− and high DOC, PO43−, and HCO3− concentrations in groundwater signify ongoing microbial-mediated redox processes favoring As mobilization in the aquifer. Other geochemical processes, e.g., Fe-oxyhydroxide reduction and carbonate dissolution, are also responsible for high As occurrence in groundwaters. Originally, gagri filters (a two-filter system with chemical powder) and later iron (Fe)-assisted biosand filters were commonly used to remove As and Fe from well water in Nepal—these two options were believed to be the best treatment option at household levels. This review focus on the description of the overall situation, including geogenic issues, occurrence of As in the sediments of the Terai, mechanisms for the release of As to the groundwater, and mitigation options.

The Provenance of Arsenic in Southeast Asia Discovered by Trace Elements in Groundwater from the Lowlands of Nepal

“…The oral intake of arsenic causes various detrimental health issues: skin lesions including pigmentation changes, mainly on the upper chest, arms, and legs, keratosis of the palms of the hands and soles of the feet, and as the most severe effect, cancer of the skin and internal organs [1][2][3]. 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][5][6][7][8][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].…”

Groundwater arsenic contamination in the Bengal Delta Plain is an important public health issue

“…At present, the category of the most severely affected countries comprises Bangladesh, India, Myanmar and Afghanistan (Chowdhury et al 2000;Khalequzzaman et al 2005;Mukherjee et al 2006;van Geen et al 2014;Hayat and Baba 2017). Several other affected Asian countries are China (Guo et al 2001;Zhang et al 2012;Xie et al 2013;Sanjrani et al 2019), Vietnam (Berg et al 2001;Buschmann et al 2008;Hanh et al 2011;Le Luu 2019), Nepal (Shrestha et al 2003;Yadav et al 2012;Mueller 2017), Cambodia (Gault et al 2008;Kim et al 2011;Murphy et al 2018), Indonesia (Winkel et al 2008;Bentley and Soebandrio 2017), Korea (Ahn 2012;Bae et al 2017) and Pakistan (Fatmi et al 2009;Brahman et al 2013;Shaikh et al 2018). The magnitude of the problem can be further gauged from a study which claimed that more than 45 million people mainly in developing countries of Asia were exposed to more than 50 µg/L of As, which was thought to be the maximum concentration limit in drinking water in several Asian countries (Ravenscroft et al 2009).…”

Effects of Untreated Drinking Water at Three Indigenous Yaqui Towns in Mexico: Insights from a Murine Model

“…Arsenic (As) is one of the most important natural pollutants in groundwater used as a drinking water source. Significant As concentrations in groundwater with detectable impacts on human health have been reported in Mexico [ 2 ], Vietnam [ 3 ], Argentina [ 4 ], Chile [ 5 ], Nepal [ 6 ], Pakistan [ 7 ], India [ 8 ], Spain [ 9 ], Taiwan [ 10 ], Thailand [ 11 ], and Bangladesh [ 12 ].…”