Bromate, chlorate, chlorite and perchlorate in sodium hypochlorite solution used in water supply

A survey was conducted to reveal the concentrations of bromate, chlorite, chlorate and perchlorate as impurities in sodium hypochlorite solutions and those of chlorate and perchlorate in raw and processed waters including a metropolitan area. High concentrations of bromate (max. 414 mg l⁻¹) and chlorate (max. 260,000 mg l⁻¹) were found in purchased sodium hypochlorite solutions for drinking water disinfection that had been stored for a long time, more than two years at a maximum. In the survey of chlorate and perchlorate in raw and processed waters in the Tone River Basin, the highest concentration of chlorate in raw water was 78 μg l⁻¹ and that of perchlorate was 40 μg l⁻¹. Chlorate and perchlorate concentrations in 32 purchased sodium hypochlorite solutions and six on-site-generated hypochlorite solutions were also analysed. In the purchased sodium hypochlorite solutions, perchlorate concentrations ranged from 0.170 to 33.0 mg l⁻¹. In hypochlorite solutions whose measured FAC (free available chlorine) concentration was lower than the manufacturer-specified FAC concentrations, the chlorate and perchlorate concentrations were higher than those in relatively fresh sodium hypochlorite solutions. In on-site-generated hypochlorite solutions, the maximum concentrations of chlorate and perchlorate were 1,700 mg l⁻¹ (140 mg g⁻¹ of measured FAC) and 0.660 mg l⁻¹ (0.053 mg g⁻¹ of measured FAC), respectively.