Perchlorate, bromate, and chlorate in hypochlorite solutions: Guidelines for utilities

On the basis of the information provided here, three potential sources of contamination for perchlorate and other oxyhalide ions were identified: background contamination from nearby agricultural activity, industrial/military sites, and/or natural deposits; formation during the treatment process itself (e.g., bromide conversion to bromate during ozonation); and via addition during the use of hypochlorite solutions containing perchlorate, chlorate, and bromate during the water treatment process. A recent article (Russell et al, 2009) estimated that a federal perchlorate regulation of 4 μg/L would result in an annual cost of approximately $76 million-$140 million per year, a cost borne by only 3.4% of public water systems. The numbers generated in that report, however, assumed that all perchlorate detected in the finished water was also present in the raw water and would need to be removed by one or more treatment technologies. Evidence from the predictive model and measured perchlorate contamination in hypochlorite solutions indicated significant potential for a 4-μg/L regulation to be exceeded. Greiner and colleagues (2008) suggested that five out of 82 bulk sodium hypochlorite solutions tested had enough perchlorate present to result in more than 4 μg/L of additional perchlorate in the finished water (above and beyond any background contamination) based on the maximum use level (MUL) of 10 mg/L FAC (NSF/ANSI, 2005). Although the 10-mg/L FAC MUL may be unrealistic for many utilities, results from the model used in the current study indicated the potential contribution of perchlorate and chlorate from hypochlorite can be significant when proper storage and handling procedures are not followed. Therefore, careful control of the quality of hypochlorite used in drinking water treatment could be equally, if not more, important for utilities operating near or above any potential federal or state MCLs resulting from source water contamination. Furthermore, utilities should be aware that the quality of hypochlorite (i.e., perchlorate, chlorate, bromate, and metal ion concentrations) being delivered to their facility could be affected by the conditions under which the hypochlorite was stored after manufacture and before delivery.