In this study, the occurrence, distribution, and ecological risk of 40 commonly used antibiotics, including 15 sulfonamides (SAs), 9 fluoroquinolones (FQs), 7 macrolides (MCs), 3 tetracyclines (TCs), 2 chloramphenicols (CAPs), and 4 other categories, in the aquatic environment of the karst plateau wetland Caohai of the Yangtze River basin in southwestern China are reported. In total, 27 antibiotics were detected, with the detection rate ranging from 5% to 100%. The total concentration at each site ranged from 21.8 ng/L to 954 ng/L, with the average concentration being 189 ng/L. FQs and MCs were the most predominant categories, contributing 29.3% and 25.0% of the total antibiotic burden. The five most commonly detected antibiotics were ciprofloxacin (CIP), oxytetracycline (OTC), acetyl sulfamethoxazole (ASMZ), norfloxacin (NOR), and florfenicol (FF). The spatial distribution of the total concentration at each site demonstrated a decreasing trend from the southeastern area upstream adjoining the main counties to the northwestern area downstream, indicating that human activities have a great impact. Meanwhile, the natural attenuation rates of different types of antibiotics in the direction of flow ranged from 17.6% to 100%, which implied the natural purification potential of the wetland for antibiotics. The cluster analysis results indicated that domestic sewage and wastewater from agriculture and animal husbandry were the main sources of contamination in the surrounding wetland. Risk quotients (RQs) assessment showed that most of the individuals were at low to medium risk and that the adverse risks posed by mixtures of antibiotics were higher than those posed by the individual antibiotics.

Polycyclic aromatic hydrocarbons (PAHs) and their substituted derivatives (SPAHs) are persistent organic pollutants derived from incomplete combustion of fossil fuels and industrial processes. These compounds are of global concern due to their carcinogenicity and environmental persistence. This study provides the first comprehensive analysis of PAH and SPAH contamination in Suzhou’s rapidly urbanizing watersheds, integrating ultra-high-performance liquid chromatography and high-resolution mass spectrometry with multidimensional risk assessment to address critical gaps in understanding pollutant dynamics in urban aquatic systems. Key findings reveal that SPAHs were significantly more abundant than parent PAHs (mean ∑19 SPAHs = 107.43 ng/L vs. ∑8 PAHs = 48.05 ng/L), with hydroxylated derivatives accounting for 67.9% of the total SPAHs, indicating active environmental transformation processes. Source apportionment identified coal combustion and industrial emissions as the dominant contributors (58.2% of PAHs), directly linking contamination patterns to localized anthropogenic activities. Notably, industrial zones exhibited unexpected toxicity hotspots, where SPAH toxicity equivalents (e.g., 3-OH-BaP) surpassed parent PAHs 2–5-fold, demonstrating substituent-driven toxicity enhancement—a critical finding for regulatory prioritization. This study advances the field by uncovering SPAHs as emerging risks in urban waterways, challenging traditional PAH-centric monitoring frameworks, and providing a novel integration of analytical chemistry and spatial risk mapping to guide targeted pollution control (e.g., prioritizing industrial discharges and non-exhaust traffic emissions). Furthermore, it highlights the urgent need for updated toxicological databases to account for substituted PAH derivatives and advocates for the regulatory inclusion of SPAHs. These insights underscore the necessity of adapting environmental policies to address complex pollutant mixtures in rapidly developing regions, emphasizing the replicability of the proposed framework for urban watershed management.