A Review of Groundwater Arsenic in the Bengal Basin, Bangladesh and India: from Source to Sink

Abstract

The groundwater of the Bengal basin, in Bangladesh and West Bengal state of India, is found to be severely polluted by non-point sourced, geogenic arsenic (As), which has been regarded as the largest public health concern in the human history. The geomorphology and geology of the aquifers play very important role in the three dimensional existence of the As in the groundwater. The provenance of the groundwater As of Bengal basin may be hypothesized to be sourced to the Himalayan orogenic belt, where the contaminant might have originated by deep-seated tectono-magmatism and subsequently introduced to the surficial system by exhumation. Later, sedimentary processes transported the As-laden sediments from the orogenic belt to the peripheral foreland basin of Bengal where, under conducive biogeochemical environment, the As is released from the solid-phase to the circulating groundwater. Ferric hydroxides and pyrite are considered to be the two most important host minerals for As, although clay minerals may also act as important substrates for the sorbed As. The mobilized As then exists in the groundwater until a suitable geochemical sink is available. The mobilization process may be related to reductive-dissolution of metal oxides and hydroxides that exist in the unconsolidated sediments of the Bengal basin. Other mechanisms like pyrite oxidation, redox cycling in surficial soils, and competitive ion exchange are also accepted as potential mechanisms for arsenic mobilization, and multiple processes may simultaneously contribute to the mobilization of As. The processes are significantly complicated by redox disequilibria in the Bengal basin aquifers. These inorganic processes may have been significantly catalyzed and accentuated by microbially mediated activities. The tertiary source of groundwater As is the irrigation return flow from the agricultural fields.

Sub-surface Biogeochemical Characteristics and Its Effect on Arsenic Cycling in the Holocene Gray Sand Aquifers of the Lower Bengal Basin

“…The total As concentration in Karimpur is within the range for BDP sediments, which varies from 0.40 to 40 mg/kg (Chakraborty et al, 2015 and references therein). However, As concentration in Karimpur is higher than the global average for unconsolidated sediments, which is around 2.00 to 7.00 mg/kg (Smedley and Kinniburgh, 2002).…”

Natural Arsenic in Global Groundwaters: Distribution and Geochemical Triggers for Mobilization

“…The occurrence and distribution of high concentrations of naturally occurring As in the groundwaters of the Southeast Asia region, particularly in the densely populated river deltas, have received much attention in recent years [22,136]. Countries of particular concern in this region include Bangladesh, West Bengal (India), China, Vietnam, Taiwan, Thailand, and Nepal because of widespread problems associated with As within their populations [1,13,137,138].…”

“…It is estimated that more than 100 million people in this region are at risk from groundwater As contamination, and so far, more than 700,000 people have been affected by As-related diseases [17]. Most groundwaters used for drinking water in rural areas of this region have been found to be contaminated with As at levels exceeding the WHO drinking water guideline of 10 μg/L [21,22].…”

“…The original source of groundwater As in the GangesMeghna-Brahmaputra basin (India and Bangladesh) may have been the formation of the Himalayan orogenic belt by deep-seated tectono-magmatism resulting in the introduction of As to the surficial system by unearthing, after which it was transported by sedimentary processes to the peripheral foreland basin, where solid-phase As is released to the circulating groundwater by biogeochemical processes [139]. The ingestion of contaminated As (directly and/or indirectly through the food chain; i.e., arsenite and arsenate) was reported to induce carcinogenesis and cardiovascular disorders in Bangladesh and West Bengal, India [23][24][25][26] (http://www.sos-arsenic.…”

“…The naturally occurring As from geochemical processes in sedimentary aquifers has the greatest effect on the largest geographic areas. In regions where groundwater is used for drinking, many people are exposed to As contamination; the As found in the sedimentary aquifers of the Bengal Delta Plain in Bangladesh and neighboring West Bengal, India, is a good example of this type of contamination [20][21][22].…”