Elevated uranium in drinking water sources in basement aquifers of southern India

Dan J Lapworth,Bentje Brauns,Somsubhra Chattopadhyay,Daren C Gooddy,Sian E Loveless,Alan M Macdonald,Andrew A Mckenzie,Sekhar Muddu,Siva N.V Nara

doi:10.1016/j.apgeochem.2021.105092

Abstract

Groundwater resources in the crystalline basement complex of India are crucial for supplying drinking water in both rural and urban settings. Groundwater depletion is recognised as a challenge across parts of India due to over-abstraction, but groundwater quality constraints are perhaps even more widespread and often overlooked at the local scale. Uranium contamination in basement aquifers has been reported in many parts of India, locally exceeding WHO drinking water guideline values of 30 μg/L and posing a potential health risk. In this study 130 water samples were collected across three crystalline basement catchments to assess hydrochemical, geological and anthropogenic controls on uranium mobility and occurrence in drinking water sources. Groundwaters with uranium concentrations exceeding 30 μg/L were found in all three study catchments (30% of samples overall), with concentrations up to 589 μg/L detected. There appears to be a geological control on the occurrence of uranium in groundwater with the granitic gneiss of the Halli and Bengaluru study areas having higher mean uranium concentrations (51 and 68 μg/L respectively) compared to the sheared gneiss of the Berambadi catchment (6.4 μg/L). Uranium – nitrate relationships indicate that fertiliser sources are not a major control on uranium occurrence in these case studies which include two catchments with a long legacy of intense agricultural land use. Geochemical modelling confirmed uranium speciation was dominated by uranyl carbonate species, particularly ternary complexes with calcium, consistent with uranium mobility being affected by redox controls and the presence of carbonates. Urban leakage in Bengaluru led to low pH and low bicarbonate groundwater hydrochemistry, reducing uranium mobility and altering uranium speciation. Since the majority of inhabitants in Karnataka depend on groundwater abstraction from basement aquifers for drinking water and domestic use, exposure to elevated uranium is a public health concern. Improved monitoring, understanding and treatment of high uranium drinking water sources in this region is essential to safeguard public health.

Highlights

India alone abstracts a third of the total annual global groundwater abstraction (Dalin et al, 2017)
The highest surface water U concentration is a river sample with 23 μg/L collected in the Vrishab havathi River, downstream of a large wastewater treatment works (WTW) in Bengaluru
Uranium concentrations in the same river up stream of the WTW were 12 μg/L by comparison, suggesting that WTW are a potential source of U in rivers and lakes

Summary

Introduction

India alone abstracts a third of the total annual global groundwater abstraction (Dalin et al, 2017). Geogenic sources of contamination can result in elevated arsenic (As) and fluoride (F) in groundwater throughout India (Podgorski et al, 2018; Mukherjee et al, 2020). This, together with the often limited groundwater treatment used in this region make the provision of good quality drinking water in many parts of India an ongoing challenge. Chemical drinking water quality is regularly monitored across India, analysis for uranium (U) is still not routinely undertaken (CGWB 2020). There have been calls for improved monitoring and management of groundwater resources and improved public engage ment to safeguard public health (Chakraborti et al, 2011; Francis et al, 2015; Coyte et al, 2018; CGWB 2020)

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Discussion

Conclusion