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The interactions between graphene oxide (GO) and antibiotics play an important role in determining their combined toxicity. However, the related information is lacking, especially for aquatic organisms. Here, we found that the combined toxicity of GO and antibiotics to a cyanobacterium Synechocystissp. PCC 6803 was dependent on their interplays. GO exhibited an additive effect with florfenicol (FLO) but an antagonistic effect with erythromycin (ETM), ofloxacin (OFL), or chlorotetracycline (CTC). Furthermore, the adsorption of antibiotics onto GO resulted in their antagonistic effects. An adsorption–isobolographic model to predict the combined effect of GO and antibiotics (γ) was developed by combining the adsorption isotherm and isobolographic method. The model was validated by the good agreement between the theoretical and experimental values of γ, and can also be used to predict the combined toxicity of carbon nanotubes and tetracycline. Proteomic analysis further revealed that the exposure to antibiotics upregulated the pathway of the ribosome but downregulated the pathway of oxidative phosphorylation, which were attenuated by the addition of GO in the co-exposure groups. Compared with the single exposure groups of antibiotics, the addition of GO downregulated the proteins related to perceiving and transmitting the signals of hyperosmotic stress, explaining the increased membrane permeability in the combined exposure groups. This study highlights the significance of pollutant adsorption onto GO in determining their combined toxicity, and calls for further studies on other types of engineered or naturally occurring carbon-based nanomaterials.

Despite many studies on the toxicity of nanomaterials or antibiotics to aquatic organisms, the combined toxicity of nanomaterials and antibiotics remains poorly understood. This study investigated the joint toxicity of carbon nanotubes (CNTs) with chloramphenicol (CAP) or tetracycline (TC) to cyanobacterium Synechocystissp. strain PCC 6803. Both reactive oxygen species (ROS) quenching experiments and proteomic analysis demonstrated that the oxidative stress caused by ROS contributed to the toxicity of CNTs but was irrelevant to the toxicity of CAP and TC despite the increased ROS levels in their exposure groups. CNTs upregulated photosynthesis significantly in response to its oxidative stress and shading effects. CAP vastly inhibited protein biosynthesis and resulted in the small size of cells. TC significantly downregulated the proteins related to periplasmic space which is responsible for cell wall biosynthesis, thereby inducing severe destruction of the cell wall. CNTs mitigated the inhibition effect of CAP on protein biosynthesis, while CAP enhanced the upregulation of proteins induced by CNTs. Consequently, an additive effect was observed between CNTs and CAP according to mortality. In contrast, CNTs exhibited an antagonistic effect with TC due to the strong adsorption and catalytic degradation of TC by CNTs. Moreover, TC can potentiate the CNT-induced downregulation of proteins related to ribosome. This study provides a more realistic insight into the molecular mechanisms of pollutant toxicity and highlights the importance of considering the different combined toxicity of multiple pollutants in the aquatic environment.

Firefighting foam is a significant source of per- and polyfluoroalkyl substances (PFAS) pollution, yet the PFAS profiles in foam formulations, particularly in China, remain unclear. Here, using target and nontarget analyses, we investigated 50 target PFAS in firefighting foams currently utilized in China, identified novel PFAS, and discovered new end products through a total oxidizable precursor (TOP) assay. We identified a total of 54 PFAS compounds (spanning 34 classes and containing seven novel PFAS) with total PFAS concentrations of 0.03–21.21 mM. Among seven novel PFAS, four PFAS met persistence, bioaccumulation, and toxicity criteria, and another PFAS had the highest ToxPi score among the identified 54 PFAS. Moreover, the predominant PFAS varied significantly in the studied foams and differed markedly from those used in other countries. After the TOP assay, nontarget analysis uncovered 1.1–55.5% more PFAS precursors and 8.25–55.5% more fluorine equivalents compared to traditional target analysis combined with TOP assay. Specifically, three double-bond perfluorinated alcohols were identified for the first time as end products of the TOP assay. This study provides crucial information for pollution control and risk assessment associated with PFAS in firefighting foam applications and emphasizes the importance of combining nontarget analysis with TOP assay in uncovering unknown PFAS precursors.

Antibiotics are anthropogenic contaminants with a global presence and of deep concern in aquatic environments, while less is known about the occurrence and risks of their transformation products (TPs). Herein, we developed a comprehensive suspect and nontarget screening workflow based on high-resolution mass spectrometry to identify unknown antibiotic TPs in wastewater treatment plant effluents. We identified 211 compounds (35 parent antibiotics and 176 TPs) at confidence levels of ≥3 and 107 TPs originated from macrolides. TPs were quantified by 17 TPs standards and semiquantified by the predicted response factors and accounted for 55.6–95.1% (76.7% on average) of the total concentrations of parents and TPs. 22.2%, 63.1%, and 18.8% of the identified TPs were estimated to be more persistent, mobile, and toxic than their parent antibiotics, respectively. Further ecological risk assessment based on concentrations and toxicity to aquatic organisms revealed that the cumulative risks of TPs were generally higher than those of parents. Despite the newly formed N-oxide TPs, the tertiary treatment process (mainly ozonation) could decrease the averaged 20.3% of concentrations and 36.2% of the risks of antibiotic-related compounds. This study highlights the necessity to include antibiotic TPs in environmental scrutiny and risk assessment of antibiotics in different aquatic environments.