Space-time distribution characteristics and risk assessment of typical antibiotics in Daxi Reservoir Basin

A solid phase extraction-high performance liquid chromatography tandem mass spectrometry (SPE-HPLC-MS) method was used to monitor six classes of antibiotics (sulfonamides, quinolones, tetracyclines, macrolides, β-lactams and chloramphenicol) in the surface water of Zucao River - Daxi Reservoir for one year, to analyze their occurrence characteristics, study their relationship with environmental factors, trace their source, and evaluate their potential risks. A total of 19 target antibiotics were detected, in which tetracyclines, quinolones, and sulfonamides were the main types of antibiotics. Temporally, except that SAs was high in summer and low in winter, the other antibiotics were basically high in winter and low in summer, with the similar trends both in spring and autumn. Spatially, the distribution pattern of the antibiotic concentration totally shows: reservoir bank zone > inflow tributary estuary> Zucao River. Spearman analysis shows that there were significant correlations between the antibiotics and environmental factors. PCA-MLR analysis shows that the antibiotics in Zucao River - Daxi Reservoir mainly came from livestock breeding wastewater, pharmaceutical wastewater, agriculture wastewater and aquaculture wastewater. Among the three target organisms (algae, invertebrates and fish), algae were the most sensitive to antibiotics. Most antibiotics were risk-free to algae, but roxithromycin, enrofloxacin, norfloxacin, and sulfamethoxazole were at risk to algae, and norfloxacin and enrofloxacin were even at medium risk. In the four seasons, the cumulative risks of 19 antibiotics to algae were present in most sampling sites with some even intermediate risk, while the average cumulative risk of Daxi Reservoir was greater than Zucao River with winter greater than summer. The cumulative ecological risk of algae was mainly from FQs while that of invertebrates and fish was mainly from SAs. Meanwhile, all the target antibiotics had no potential health risks to the human body, but they still need attention.