Sulfonamides and their transformation products in the Yellow River Delta, China: Occurrences, source apportionment, and ecological risks.

Sulfonamides (SAs) have aroused general concerns due to their extensive application and contribution to antibiotic-resistance genes. Previous studies mainly concentrated on parent SAs in the water, but little information is available about the pollution profiles and partitioning of numerous transformation products in different matrices. In this study, water and sediment samples of 64 sampling sites from the Yellow River Delta (YRD) were simultaneously investigated for 27 target SAs to explore their partitioning, spatiotemporal variations, pollution sources, and ecological risks. Twenty-six of the SAs were detected with concentrations ranging from not detected (ND) to 442 ng/L in water and ND to 5.4 ng/g dry weight (dw) in sediment. The predominant compounds differed between water and sediment because of variation in SAs hydrophobicity. The partitioning coefficients (Kd) between water and sediment were highly variable (1.4-5750 L/kg) among different SAs and different sites. A significant positive correlation (p < 0.01) between log Kow and log Kd was observed, and the properties of sediment were also important factors influencing the partitioning of SAs. The concentrations of SAs in water samples exhibited temporal and spatial variations, and human activity and hydrodynamic condition were the main factors affecting their spatial distribution. Treated domestic wastewater was the predominant pollution source (contributed to 42 % of the total pollution) in the YRD, and aquaculture also had a considerable contribution (19 %). Risk assessment showed that moderate or high risks might be produced by SAs to aquatic organisms, especially sensitive algae. Most SAs posed minimal or low risks for antibiotic resistance (AR) development.