Coastal antibiotics hotspots: Decoding spatiotemporal drivers and risk gradients in Chinese marine ecoregions.

The environmental impact and resistance issues of antibiotics have drawn global concern. However, there is still a lack of in-depth understanding regarding antibiotic pollution in coastal bays at different latitudes in China. This work systematically explored the spatiotemporal distribution, potential sources, and ecological risks of antibiotics in seawater from coastal bays of China at different latitudes during different seasons. Twenty-one antibiotics were detected in seawater samples, primarily including quinolones, sulfonamides, tetracyclines, macrolides, and chloramphenicols. A widespread distribution of these antibiotics (>50 % detection rates) was detected in the coastal seawater of China. Florfenicol (FF) and tetracycline (TET) were the predominant antibiotics in the seawater from different latitude bays of China. The antibiotic levels were higher in autumn, with concentrations ranging from 4.40 ng/L to 22.17 ng/L (mean: 8.69 ng/L). Seawater from the northern bays had relatively higher antibiotic concentrations. The highest concentration of antibiotics was found in Jiaozhou Bay during the autumn, with levels ranging from 7.39 ng/L to 22.17 ng/L (13.88 ng/L). Aquaculture, livestock farming, and medical use were identified as primary sources. Ecological risks were generally low, except for moderate risk from ofloxacin (OFL) at station A5 in the autumn of Jiaozhou Bay.