Liqun Xing

The toxicological mechanism(s) of polychlorinated diphenyl ethers (PCDEs) in vertebrates remains unresolved. To test the hypothesis that PCDE-induced acute lethality and developmental toxicity are mediated by aryl hydrocarbon receptor (AHR) activation, wild-type, Tg(cyp1a:gfp) transgenic, and Ahr2-null zebrafish were exposed to 11 PCDE congeners commonly detected in the environment. Compared to wild-type zebrafish, where Ahr2 activation was confirmed by robust GFP induction in Tg(cyp1a:gfp) larvae, Ahr2-null larvae exhibited significantly reduced mortality and malformation percentages (e.g., 68.7-78.8% and 48.3-97.2% lower for three highly potent congeners CDE 15, 37, and 118, respectively), demonstrating Ahr2 as the primary mediator of PCDE-induced toxicity. Furthermore, complementary in vitro species-specific luciferase reporter gene (LRG) assays revealed significant dioxin-like activities of PCDEs in zebrafish, avian (chicken, pheasant, quail), and rat models, with interspecies potency variations of up to 27,000-fold. Notably, some PCDEs exhibited relative potencies comparable to or exceeding those of known dioxin-like compounds, including HO-/MeO-polybrominated diphenyl ethers, polychlorinated diphenyl sulfides, and several highly halogenated dibenzo-p-dioxins and dibenzofurans. Overall, these findings indicate that AHR activation serves as the primary molecular mechanism underlying the toxicity of PCDEs in vertebrates and provide critical data for ecological risk assessment. Given their structural similarity to dioxins and significant bioaccumulation potential, PCDEs should be considered for inclusion in global toxicity equivalency factor frameworks.

The excessive use of antibiotics contributes significantly to environmental pollution and the widespread presence of antibiotic resistance genes (ARGs), which poses a serious threat to aquatic ecosystems and human health. Despite being a critical source of antibiotics and ARGs in the environment, research exploring their occurrence and removal characteristics in township wastewater treatment plants (WWTPs) remains limited. This study investigated the abundance and removal efficiencies of 39 antibiotics and 8 ARGs in influent and effluent samples from 40 township WWTPs located in the upper reaches of the Yangtze River. Antibiotics were detected in both influents and effluents, with detection frequencies (DFs) ranging from 2.44% to 100%. In contrast, all targeted ARGs exhibied 100% DFs in both influents and effluents. The average concentrations of antibiotics in influents and effluents were 370.67 ng/L and 242.06 ng/L, respectively, and the ARGs concentrations were 9.88 × 10⁶ and 7.10 × 10⁵ copies/mL, respectively. Among the antibiotics analyzed, macrolides and fluoroquinolones accounted for over 70% of the total antibiotic concentrations in both influent and effluent samples. Additionally, sul1 and sul2 were identified as the predominant ARGs, constituting more than 99% of the total abundance in both influent and effluent samples. Notably, significant correlations between the ARGs and their respective antibiotics were not consistently observed. The average removal efficiencies for total antibiotics and ARGs by township WWTPs were 34.70% and 93.30%, respectively. Furthermore, all calculated ecological risk values (risk quotient, RQ) for individual antibiotics in effluent samples were below one, except for oxytetracycline, which had RQ values greater than one in three effluents. The total RQs, representing the sum of individual RQs, indicated that 11 effluents presented a high risk (27.50%), while 17 effluents exhibited a moderate risk (42.50%). These findings suggest that township WWTPs may represent a significant source of antibiotics and ARGs in the environment, necessitating further process improvements for their effective elimination. Graphical abstract