Water quality, microcystin-LR, and Cylindrospermopsin contamination status of spring and dug well water in CKDu high, low, and non-prevalent areas of Sri Lanka

Cyanotoxins, Microcystin LR (MC-LR) and Cylindrospermopsin (CYN) are hepato and nephro toxins and considered as one of the hypotheses for Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka. Recent studies have revealed that significant number of dug wells in the North Central and Uva provinces where CKDu is prevalent are contaminated with cyanotoxins MC-LR and CYN. In the present study, cyanotoxin; MC-LR, CYN, and potential toxin-producing cyanobacteria were studied in 330 dug wells and 9 spring water samples collected from CKDu high prevalent areas in several Divisional Secretariats (DS) and Grama Niladhari (GN) divisions of Anuradhapura (Padaviya DS, Medawachchiya DS, Kebithigollewa DS), Polonnaruwa (Medirigiriya DS), Badulla (Girandurukotte GN) and Ampara (Dehiaththakandiya DS) districts, low prevalent areas in Anuradhapura district (Galnewa DS, Rajanganaya DS), non-prevalent areas in Angunakolapelessa DS of the Hambanthota district. General water quality parameters: temperature, pH, conductivity, Dissolved Oxygen (DO), Nitrate (N-NO₃^-), Nitrite (N-NO₂^-), Ammonia (N-NH₃), Total Phosphorus (TP), and Total Hardness (TH) were determined using standard spectrophotometric and titrimetric methods. BACON test kits were used following manufactures instructions to quantify the CYN, and MC-LR concentrations by using the ELISA plate reader. Cyanobacteria density and species composition were determined under light microscopy following the standard algae and cyanobacteria keys. With the exception of Electrical Conductivity, all of the water quality parameters tested remained within the SLSI drinking water quality standard range. Microcystis spp. cell densities ranged from 14±3 to 1590±256 cells mL-1, where MC-LR concentration ranging from 0.04±0.01 to 3.89±0.02 µg L^-1. At different CYN concentrations (0.04±0.01 to 3.59±0.05 µg L^-1), Cylindrospermopsis spp. cell densities varied from 15 ±4 to 615±112 cells mL-1. Well water collected from Hambanthota district and spring water was collected Kebithigollewa DS, in Anuradhapura did not record cyanotoxins and cyanobacteria. The factor analysis classified well waters into three clusters of high, low, and non-prevalence areas with presence and absence of cyanobacteria and cyanotoxins. In contrast, springs were classified to a separate cluster. High concentrations of MC-LR and CYN were found in wells where CKDu high prevalent 85% of Padaviya DS and 80% of Medirigiriya DS, respectively. High Nitrate-N (3.01±0.56 mg L^-1) and Nitrite-N (0.69±0.09 mg L^-1) concentrations were recorded in well water collected from high CKDu prevalence areas. Thus, the results of the present study showed a relationship between cyanobacteria, cyanotoxins and CKDu records in the study area. Accordingly, further comprehensive studies are needed to be carried out to confirm the relationship between cyanotoxins and CKDu in Sri Lanka as cyanotoxin were listed in the WHO report as one of the possible reasons for CKDu.