Spatial distribution, source apportionment and risk assessment of antibiotics in the surface water and sediments of the Yangtze Estuary

The "pseudo-durability" of antibiotics in estuaries is gaining increasing interest, especially in the Yangtze Estuary, a vital water supply source for the Shanghai city. To clearly describe the pollution level and risk of antibiotics in this estuary, the contents of 8 typical antibiotics in the surface water and the sediment along the nearshore zone and in the estuarine channel in the estuary were comprehensively analyzed. The results revealed that sulfonamides and tetracycline are the predominant antibiotics in the surface water, while tetracyclines and fluoroquinolones are the dominant ones in the sediments. The ranges of the eight antibiotic concentrations between the nearshore zone (not detected to 7.06 ng/L for water, below LOD to 10.94 ng/g for sediment) and the estuarine channel (not detected to 8.46 ng/L for water, not detected to 14.84 ng/g for sediment) showed no notable differences, but the degree of scatter was different for each antibiotic. The spatial distribution was different for each antibiotic in the north branch and the south branch; higher values for most of the target antibiotics were observed in the south branch of the estuary. The distribution and source analysis from a GIS map using the kriging method indicated that runoff input and the antibiotic residues from aquaculture were the two major sources of the antibiotic pollution in the Yangtze Estuary. A risk assessment of the individual antibiotic exposure in the surface water showed that sulfamethoxazole, ofloxacin and ciprofloxacin, tetracycline and oxytetracycline, and sulfadiazine, roxithromycin and erythromycin in this area exhibited a medium risk, low risk and almost no risk to the selected aquatic microorganisms, respectively.