The aim of this study was to evaluate if chlorate, chlorite, perchlorate and bromate ions are found in treated water from 16 Canadian drinking water treatment plants (WTPs) that use hypochlorite as a disinfectant. The WTPs in this survey had unusually high concentrations of sodium, bromide and dissolved organic carbon in the source water and all used ammonium in the treatment train. Samples of hypochlorite solutions used in the disinfection process were collected in addition to source water and treated water. Chlorite was not detected in any of the samples (MDL 21 μg/L). Chlorate was found in 83% of source water samples (between 0.002 and 0.25 mg/L) and in treated water (between 0.002 and 0.96 mg/L), with the exception of one treated water sample (1.6 mg/L); 38% of them exceeded the US EPA health reference value of 0.210 mg/L. Perchlorate was detected in 47% of source water samples (between 0.06 and 0.2 μg/L) and in treated water (between 0.06 and 5.7 μg/L). Bromate was detected in only one source water sample and was found in treated water (between 0.5 and 11.2 μg/L). Only treated water samples from one WTP were above the US EPA maximum contaminant level of 10 μg/L.

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