This study was aimed at considering an analytical method to determine the concentrations of fipronil and four fipronil degradation products (fipronil sulfide, fipronil desulfinyl, fipronil sulfone, and fipronil detrifluoromethyl sulfinyl). We analyzed these compounds in raw and drinking water samples from water purification plants in Osaka, Japan. Fipronil, fipronil sulfide, fipronil desulfinyl, and fipronil sulfone were detected in raw water, whereas fipronil sulfide and fipronil desulfinyl were detected in drinking water. It was necessary to monitor not only fipronil but also its degradation products because the composition rate of degradation products was higher than that of fipronil. The concentrations of fipronil and its degradation products in drinking water were lower than those in raw water. Therefore, these compounds are being removed by the current water treatments such as sand filtration, ozonation, and activated carbon treatment. The concentrations of fipronil and its degradation products were considerably low compared with the target value (0.0005 mg/L) for fipronil in Japan.

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