Status of cyanotoxin contamination and water quality in major irrigational and recreational reservoirs in Sri Lanka

The rapid depletion of water quality in reservoirs is considered as a global ecological and health consequences. Hence, the regular monitoring of water quality status in such reservoirs is mandatory to ensure a safe water supply for the general public. The present study was conducted to evaluate the water quality, contamination status of cyanotoxins, species composition and abundance of phytoplankton in 43 selected major reservoirs in Sri Lanka. The water temperature, pH, Dissolved oxygen (DO), and Electrical Conductivity (EC) were measured at the site and the other water quality parameters, Total Nitrogen (TN), Total Phosphates (TP), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), Fluoride, Total Hardness (TH), Chlorophyll-a (Chl-a), Cyanotoxins; Microcystin-LR (MC-LR), Cylindrospermopsin (CYN), Saxitoxin (SAX), Nodularin (NOD), Anatoxin-a (ANA-a) concentrations and Faecal Coliform were measured following the standard methods. The water temperature, pH, DO, EC, TN, TP, COD, BOD, Fluoride, TH, and Chl-a were ranged from 20.5 to 29.7 ℃, 6.5 to 8.8, 2.1 to 7.9 mg/L, 25.6 to 1752 µS/cm, < 0.05 to 3.42 mg/L, < 0.05 to 20.55 mg/L, 10.2 to 220.6 mg/L, 0.6 to 10.6 mg/L, < 0.01 to 0.23 mg/L, 13.67 to 122 mg/L and 0.66 to 48.9 µg/L respectively. Further, each water body was contaminated with at least one algal toxin tested. Overall, MC-LR was the most dominant toxin variant (37%) in the collected water samples compared to CYN (10%), SAX (10%), NOD (10%), and ANA-a (10%). Moreover, 39 reservoirs tested out of 43 recorded fecal coliform greater than 200 (CFU)/100 mL. Among all the selected water bodies, Beira Lake in Colombo was the most polluted recreational water body. Furthermore, in Beira Lake, almost all measured water quality parameters exceeded the standard levels set by the Sri Lanka Standards Institute (SLSI) and the Environmental Protection Agency (EPA), USA for aquatic life. The measured water quality data indicated that most of the reservoirs are polluted, and the overall water quality has deteriorated. It suggests the negative impacts on the ecological balance of the ecosystem and these results indicate the necessity of proper treatment facilities for the reservoirs in Sri Lanka.