Occurrence and ecological hazard assessment of selected antibiotics in the surface waters in and around Lake Honghu, China

The occurrence and temporal–spatial distributions of 13 antibiotics (tetracyclines, sulfonamides, and fluoroquinolones) in the water of a high-intensity aquaculture lake, Honghu Lake, and its associated river network and ponds were investigated. Tetracycline, oxytetracycline, chlortetracycline, and sulfadiazine are the four dominant antibiotics in this region, with maximum and median concentrations of 1454.8 and 304.8 ng/L, 2796.6 and 161.9 ng/L, 1431.3 and 349.9 ng/L, and 499.5 and 106.5 ng/L, respectively. The median concentrations of the other nine antibiotics are lower than 57.1 ng/L. The highest contaminated sites are located in the Four-lake main canal and its lake inlets. Antibiotic concentrations were higher in November than in May and the concentrations were strongly correlated with water temperature, dissolved oxygen, and nitrates according to redundancy analysis. The source analysis indicated that besides untreated domestic and husbandry sewage, the aquaculture in the lake and ponds is a main source of antibiotics in the study region. The environmental hazards posed by the selected antibiotics were assessed by using the methods of hazard quotient and mixture hazard quotient. The results suggested that tetracycline, oxytetracycline, sulfadiazine, and ciprofloxacin pose medium to high ecological hazard to algae in almost all of the water samples, and the high combination ecological hazards of antibiotics are mainly posed by the high individual hazard quotient of tetracycline in the study area.