AWWA WQTC62523

The objective of this study was to evaluate the quality of raw and treated water from six treatment plants in Quebec whose water supply is affected by cyanobacterial blooms. High levels of cyanobacteria were identified in raw water samples collected from all six plants from July to November 2001-2004. At least one cyanotoxin was detected in 43% of the samples, with up to 5.3 µg/L of microcystins and 2.3 µg/L of anatoxin-a. Given the threat to human health posed by the ingestion and inhalation of cyanotoxins and cyanobacteria, their levels in raw water demonstrate the need for effective treatments to remove them. Samples from the six plants showed that, in general, treated water contained very low levels of cyanobacteria (around 200 cells/mL), and low turbidity levels (<0.5 NTU). Moreover, only 5% of the treated water samples had detectable concentrations of cyanotoxins, with a maximum value of 0.1 µg/L for microcystin-LR (10 to 15 times lower than recommended maximum available concentrations). While confirming the safety of the drinking water produced by the six treatment plants currently affected in Quebec, the study also showed that the plants are vulnerable to the impacts of pollution, and pointed to the need to further protect and restore lakes and rivers that serve as drinking water sources. Includes 15 references, tables, figure.