Occurrence of bromate, chlorite and chlorate in drinking waters disinfected with hypochlorite reagents. Tracing their origins

Bromate was first reported as a disinfection by-product from ozonated waters, but more recently it has been reported also as a result of treatment using hypochlorite solutions worldwide. The aim of this study was to study the scope of this phenomenon in the drinking waters (n = 509) of Castilla y León, Spain, and in the hypochlorite disinfectant reagents. Two thirds of the treated waters monitored were found to have bromate concentrations higher than 1 µg/l, and of them a median value of 8 µg/l and a maximum of 49 µg/l. These concentrations are higher than those reported so far, however, a great variability can be found. Median values for chlorite were of 5 µg/l, and of 119 µg/l for chlorate. Only 7 out of 40 hypochlorite feedstock solutions were negative for bromate, the rest showing a median of 1022 mg/l; and 4 out of 14 calcium hypochlorite pellets were also negative, the rest with a median of 240 mg/kg. Although bromate is cited as potentially added to water from calcium hypochlorite pellets, no reference is found in scientific literature regarding its real content. Chlorite (median 2646 mg/l) and chlorate (median 20,462 mg/l) and chlorite (median 695 mg/kg) and chlorate (median 9516 mg/kg) were also monitored, respectively, in sodium hypochlorite solutions and calcium hypochlorite pellets. The levels of chlorite and chlorate in water are considered satisfactory, but not those of bromate, undoubtedly owing to the high content of bromide in the raw brines employed by the chlor-alkali manufacturers. Depending on the manufacturer, the bromate concentrations in the treated waters may be very heterogeneous owing to the lack of specification for this contaminant in the disinfectant reagents —the European Norms EN 900 and 901 do not mention it.