Geo-environmental assessment of geochemistry of groundwater and associated human health risks in the dry zone terrain of Sri Lanka

The close association between the geographic distribution of certain diseases and environmental factors is clearly apparent in the tropical terrain of Sri Lanka. Among these diseases, dental and skeletal fluorosis and Chronic Kidney Disease of uncertain aetiology (CKDu) are common problems in the dry zone regions of the country. The quality of drinking water is primarily blamed for the emergence of such diseases. Since 2015, about 1250 groundwater samples from the dry zone region of Sri Lanka were collected and analyzed for their water quality parameters. Excessive ionic concentrations were observed in groundwater in which solute composition is dominated by Na+, K+, Ca2+, Mg2+, HCO3 ˉ, Clˉ, and SO4 2ˉ. The results revealed that the dry zone was highly affected by excessive levels of fluoride and divalent cations. Fluoride content in the study samples varied up to 6.8 mg/L. About 35% and 73% of samples from metamorphic and sedimentary terrains, respectively, were identified as very hard and not palatable. Higher As content is a significant feature in groundwater from the sedimentary terrain in the north and northwest of the island. Excessive nitrate was also noted in highly permeable sandy aquifers in the coastal belt. Results of available water quality data confirm that the groundwater quality of the dry zone is affected by both geogenic and anthropogenic factors, while certain geographically distributed health issues are closely associated with the groundwater geochemistry.