Abstract
Chlorate and bromate were detected in high concentrations in outdoor pool water in the Tama area, Tokyo, in a survey of disinfection by-products. In order to consider the cause of such high concentration and a method of reducing the amounts of these compounds, we investigated the concentrations and variation of chlorate and bromate in pool water and in the sodium hypochlorite used in the pool facilities. In addition, our survey data of pool water and pool facilities were analyzed in detail. As a result of the investigation, it was found that there was no apparent difference in the quality of the sodium hypochlorite used in outdoor and indoor pool facilities; hence, another cause of the high concentration of chlorate in the outdoor swimming pool water was suspected. From the analysis of the correlation of the chlorate concentration and chloride ion concentration in pool water, it was shown that an overuse of sodium hypochlorite at more than the required amount for sterilization in outdoor pools is a possible cause. In order to reduce the chloric acid concentration in pool water, it may be effective to control the dose of sodium hypochlorite, on the basis of the chloride ion concentration as an indicator, and to dilute pool water by replenishing the water.
