Temporal Variation of Heavy Metal Concentrations in Drinking Water in North Central Sri Lanka Related to Chronic Kidney Disease of Unknown Etiology (CKDU)
Peiris, Inoka Marian Shyamali
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Annually 1400 people in Sri Lanka fall victim to kidney failure and untimely death due to Chronic Kidney Disease of Unknown etiology (CKDu). The cause of CKDu remains uncertain despite several years of study. Studies so far have suggested that some combination of groundwater chemistry, genetic predisposition, and occupational exposure are the causes of CKDu. Geographical overlap of Dry Zone and CKDu area provides primary evidence for a strong environmental component to the disease. Our hypothesis was that cycling of subsurface redox state driven by extreme recharge variation between monsoon and dry season in the study area masks an important source of the heavy metals associated with CKDu. Heterogeneous distribution of CKDu suggests environmental contributors themselves are heterogeneous. Primary hydrochemical controls of the study area are fresh monsoon recharge, evaporation and water-rock interaction at depth. Chemical results strongly suggest a water-rock interaction origin for differing hydrochemical types of groundwater in close proximity. Apparent groundwater divides present in the basement of the aquifer in the groundwater model and the trace element correlation support above statement. This segmentation of aquifer offers a potential mitigation tool by avoidance of higher risk areas and /or higher risk zones in aquifer. ICP-MS analysis of water samples collected throughout the study period shows that trace metal concentrations including known nephrotoxics such as Cd and As levels in the water are well below the WHO recommended limits but shows temporal as well as spatial variation. Heavy metal concentrations in groundwater can change spatially and temporally due to various reasons. Extreme wet and dry conditions that causes extreme water level changes in the aquifers results in changes in the oxidation state of the surrounding environment causing temporal variation in heavy metal concentration. So wet and dry seasons can introduce cyclic highs and lows in redox sensitive element concentrations in aquifers. Cyclic increasing and decreasing of arsenic concentrations through dry and wet seasons observed in the study area through study period is similar to reports of Asian arsenic crisis, but the concentrations are very low in the study area both in wet and dry seasons. Similar to cyclic variation of arsenic concentration, redox cycling or cyclic high and low concentrations during dry and wet seasons can be seen with Fe and Mn. People used to highly depend on groundwater for consumption in NCP. But with CKDu people afraid of drinking groundwater turned to small scale reverse osmosis plants installed in the area by government organizations and private parties and maintained by community-based organizations. RO process can purify water by removing hardness and known nephrotoxins such as arsenic and cadmium. However long term effect of RO water consumption and RO waste disposal without any treatment to the ground surface is a concern. Our findings reveals that RO reject disposal to the ground surface without any treatment has affected the aquifer of the area. Total dissolved solids as well as fluoride concentrations in water from wells down gradient from RO plants are high and shows an increasing trend with time. Segmented nature of the aquifer provides a possible solution for aquifer contamination by RO water waste. Aquifer segments that are known to have higher CKDu incidences should be avoided and these segments can be used as disposal sites for RO waste.