Arsenic pollution of groundwater in Vietnam exacerbated by deep aquifer exploitation for more than a century

Abstract

Arsenic contamination of shallow groundwater is among the biggest health threats in the developing world. Targeting uncontaminated deep aquifers is a popular mitigation option although its long-term impact remains unknown. Here we present the alarming results of a large-scale groundwater survey covering the entire Red River Delta and a unique probability model based on three-dimensional Quaternary geology. Our unprecedented dataset reveals that ∼7 million delta inhabitants use groundwater contaminated with toxic elements, including manganese, selenium, and barium. Depth-resolved probabilities and arsenic concentrations indicate drawdown of arsenic-enriched waters from Holocene aquifers to naturally uncontaminated Pleistocene aquifers as a result of >100 years of groundwater abstraction. Vertical arsenic migration induced by large-scale pumping from deep aquifers has been discussed to occur elsewhere, but has never been shown to occur at the scale seen here. The present situation in the Red River Delta is a warning for other As-affected regions where groundwater is extensively pumped from uncontaminated aquifers underlying high arsenic aquifers or zones.three-dimensional risk modeling | anthropogenic influence | drinking water resources | geogenic contamination | health threat

Release of arsenic to deep groundwater in the Mekong Delta, Vietnam, linked to pumping-induced land subsidence

“…As such, our understanding of the extent and mechanisms of deep arsenic contamination has remained incomplete. Evidence suggests that deep contamination in the Mekong Delta focus area is unlikely to have been caused by the only presently acknowledged mechanism: pumping-induced vertical migration of arsenic or dissolved organic carbon (DOC), which can trigger arsenic release, from the surface or shallow subsurface (6,7,(19)(20)(21). The number of wells above 10 μg/L in the deep zone is seven times greater than in the shallow zone.…”

“…"Dig deep to avoid arsenic" (3) has been touted as a safe answer to the provisioning of drinking water in Bangladesh, despite a lack of evidence that deep aquifers indeed remain uncontaminated under prescribed (4,5) or unregulated pumping. In fact, recent studies indicate that arsenic occurrence may be on the rise where deep aquifers are intensively pumped in parts of Bangladesh, West Bengal, India and the Red River Delta, in northern Vietnam (6)(7)(8). In some cases, isolated deep arsenic contamination may be caused by downward leakage through well bores.…”

“…Across basins, dissolved arsenic concentrations tend to be highest in the shallow (<100 m) subsurface (10), where the reactivity of host minerals and the organic carbon needed to dissolve them is also greatest (11,12). As a result, considerable attention has been paid to contamination mechanisms in Holocene units (up to ∼0.011 Ma in age), where affected wells are most commonly found, and to older Pleistocene units (∼0.011-2.6 Ma), where they are usually more rare (6)(7)(8)13). Little is known of arsenic occurrence in older Pliocene-Miocene-age (∼2.6-23 Ma) aquifers or in the thick sequences of interbedded confining clays (i.e., aquitards), which are known to mobilize high levels of dissolved arsenic in nearsurface Holocene clays (12).…”

Water Demand Management: A Strategic Approach towards a Sustainable Urban Water System in Hanoi

“…In fact, the results of analyzed water samples exceeded the allowable level from 20 to 30 times higher. For example, in Phap Van groundwater wells, the ammonia level was 30 mg/L (see Dung, 2007;Winkel et al, 2011). A similar study conducted by Dan and Dzung (2002) also showed that the concentration of ammonia and oxidation are increasing with time and normally, concentrations in the upper aquifer is higher than in the lower aquifer in Hanoi area, indicating that pollutants migrate downward.…”

Predicting the risk of arsenic contaminated groundwater in Shanxi Province, Northern China

“…Logistic regression has been successfully used to assess the probability that As concentrations exceed a pre-defined threshold Twarakavi and Kaluarachchi, 2006;Winkel et al, 2011).…”