[Spatiotemporal Variation of Antibiotic Pollution and Multi-level Ecological Risk Assessment in the Nandu River...

To reveal the spatiotemporal variation of antibiotic pollution in the Nandu River Basin, Hainan Province, and assess its ecological risk, a large-volume injection-high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was used to quantitatively analyze 44 antibiotics from five major categories. The risk quotient (RQ) and joint probability curves (JPCs) methods were employed for ecological risk assessment. The results showed that 10 antibiotics were detected in the Nandu River Basin, with total concentrations ranging from ND to 2 034.38 ng·L^-1. Sulfachloropyridazine had the highest concentration (ND-1 993 ng·L^-1), followed by sulfamethoxazole (ND-949.81 ng·L^-1) and florfenicol (ND-482.16 ng·L^-1). The mean antibiotic concentrations in different hydrological periods were as follows: normal water period (112.92 ng·L^-1) > dry season (78.29 ng·L^-1) > wet season (69.85 ng·L^-1). The RQ method indicated that sulfamethoxazole, trimethoprim, lincomycin, erythromycin, and clindamycin posed high risks, with risk quotients of 9.50, 7.59, 2.99, 2.43, and 1.34, respectively. The exceedance rates of the predicted no-effect concentration (PNEC) for these five antibiotics were 11.9%, 4.76%, 4.76%, 4.76%, and 2.38%, respectively. The JPCs-based assessment showed that erythromycin had the highest risk product (3.45%), indicating a moderate risk, while lincomycin had a maximum risk product of 0.67%, indicating a low risk. The risks of other antibiotics were negligible. The results of ecological risk assessment were influenced by antibiotic concentration, detection frequency, and toxic effects. By constructing a multi-tiered ecological risk assessment approach, this study scientifically defined ecological risk thresholds for antibiotics, effectively addressing the potential issues of underprotection or overprotection in traditional assessment methods. This provides a scientific basis for hierarchical management and spatially differentiated control of antibiotic pollution at the regional scale.