Abstract
Poor drinking water quality in household wells is hypothesised as being a potential contributor to the high prevalence of chronic kidney disease of uncertain aetiology (CKDu) among the farming communities of the Medawachchiya area, Anuradhapura, Sri Lanka. One of the natural processes that can affect water quality is the dissolution of minerals contained within an aquifer by water–rock interactions (WRIs). Here we present a comprehensive assessment of WRIs and their influence on the water chemistry in household wells and spring waters in the Medawachchiya area by combining measurements of environmental isotopes, such as strontium, lithium and stable carbon isotopes and inorganic chemistry parameters, and modelling geochemical mass balance reactions between rainfall and groundwater samples. Our results reveal the presence of strontium, dissolved from both silicate and carbonate minerals, with high isotopic (87Sr/86Sr) ratios of up to 0.7316. Geochemical mass balance modelling and prior 87Sr/86Sr studies on the Wanni Complex bedrock suggest these strontium values may be the result of biotite dissolution. We also identify lithium and uranium contributed from the dissolution of silicates, albeit at concentrations too low to constitute a known health risk. In contrast, the levels of magnesium and calcium in our samples are high and demonstrate that, despite the felsic bedrock, well water chemistry in the Medawachchiya area is dominated by carbonate dissolution.
Highlights
Chronic kidney disease of uncertain aetiology (CKDu) in Sri Lanka was first reported in 1996
Groundwater chemistry in Sri Lanka is largely determined by water–rock interactions (WRIs), ion exchange and precipitation processes[20]
Using 87Sr/86Sr, δ7Li and dissolved inorganic carbon (δ13CDIC) combined with major ion analyses, we show how WRIs affect water quality of 30 domestic well and spring waters used for drinking water purposes in a CKDu-impacted region, Medawachchiya, Sri Lanka
Summary
Chronic kidney disease of uncertain aetiology (CKDu) in Sri Lanka was first reported in 1996. One hypothesis is that drinking water contaminants may be a causal or contributing factor to the disease[2,3,4,5]. Groundwater chemistry in Sri Lanka is largely determined by water–rock interactions (WRIs), ion exchange and precipitation processes[20]. Ca and Mg take the place of adsorbed Na on aquifer solids through cation exchange processes since the interaction between sorption sites and divalent ions is typically much higher than monovalent ions. This results in an increase in dissolved Na concentrations and a decrease in dissolved Ca and Mg concentrations[23]
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