Determination and occurrence of sulfonamide transformation products in surface waters.

The transformation products of sulfonamides (SAs) have raised increasing environmental and health concerns in recent years, but information on their analysis and environmental fates remains limited. In this study, an analytical method using liquid chromatography with tandem mass spectrometry (LC-MSMS) was optimized to simultaneously analyze 9 SA transformation products and 14 SAs in water samples. This method was applied to investigate the occurrence of antibiotics in three urban rivers in Beijing, and all of the target compounds were detected. N-acetylsulfamethoxazole, N-acetylsulfapyridine, and N-acetylsulfamethazine were found to be the predominant acetyl SAs in the aquatic environment, and high frequencies of hydroxylated SA (5-hydroxysulfapyridine) and glucuronide-conjugated SA (sulfamethoxazole β-D-glucuronide) were also detected. The SA transformation products accounted for 22-32% of the total concentrations of SAs and their transformation products in the water samples. The pollution levels of the compounds exerted only minor effects on the proportions of the SA transformation products. The compound-specific transformation of sulfamethoxazole, sulfapyridine, and sulfadiazine in the water samples was consistent with their acetylation efficiencies in metabolic processes in organisms, which suggests that the SA-acetylated products were derived mainly from biological metabolism in humans or animals. This finding was supported by the fact that environmental degradation exerts a weak effect on SA profiles in the water samples.