Polychlorinated diphenyl ethers (PCDEs) are a class of synthetic halogenated aromatic compounds, which have gradually attracted widespread attention due to potential environmental risks to humans and ecosystems. This paper presents a literature review of research on PCDEs using PubMed, Web of Science and Google Scholar as search engines/databases with no constraints on publishing year or number. A total of 98 publications on the sources, environmental levels, environmental behavior and fate, synthesis and analysis and toxicology of PCDEs were retrieved. Existing studies have shown that PCDEs widely exist in the environment with the ability of long-range transport, bioaccumulation and biomagnification, which are almost comparable to polychlorinated biphenyls. They can elicit adverse effects including hepatic oxidative stress, immunosuppression, endocrine disorders, growth retardation, malformations, reduced fertility and increased mortality in organisms, among which some seem to be related to the activation of the aryl hydrocarbon receptor. PCDEs can be metabolized into other organic pollutants, such as hydroxylated and methoxylated PCDEs and even polychlorinated dibenzo-p-dioxins and furans through biotransformation, photolysis and pyrolysis reactions in the environment. Compared with reviews on PCDEs published previously, some new information and findings are summarized in this review, such as new sources, current environmental exposure levels, main metabolism pathways in aquatic organisms, acute toxicity data for more species and relationships between structural parameters and toxicity and bioaccumulation potentials of PCDE congeners. Finally, current research deficiencies and future research perspectives are proposed to facilitate the assessment of health and ecological risks of PCDEs.

Understanding the adsorption behavior of antibiotic molecules on minerals is crucial for determining the environmental fate and transport of antibiotics in soils and waters. However, the microscopic mechanisms that govern the adsorption of common antibiotics, such as the molecular orientation during the adsorption process and the conformation of sorbate species, are not well understood. To address this gap, we conducted a series of molecular dynamics (MD) simulations and thermodynamics analyses to investigate the adsorption of two typical antibiotics, tetracycline (TET) and sulfathiazole (ST), on the surface of montmorillonite. The simulation results indicated that the adsorption free energy ranged from - 23 to - 32 kJ·mol^-1, and - 9 to - 18 kJ·mol^-1 for TET and ST, respectively, which was consistent with the measured difference of sorption coefficient (K_d) for TET-montmorillonite of 11.7 L·g^-1 and ST-montmorillonite of 0.014 L·g^-1. The simulations also found that TET was adsorbed through dimethylamino groups (85% in probability) with a molecular conformation vertical to the montmorillonite's surface, while ST was adsorbed through sulfonyl amide group (95% in probability) with vertical, tilted and parallel conformations on the surface. The results confirmed that molecular spatial orientations could affect the adsorption capacity between antibiotics and minerals. Overall, the microscopic adsorption mechanisms revealed in this study provide critical insights into the complexities of antibiotics adsorption to soil and facilitate the prediction of adsorption capacity of antibiotics on minerals and their environmental transport and fate. This study contributes to our understanding of the environmental impacts of antibiotic usage and highlights the importance of considering molecular-level processes when assessing the fate and transport of antibiotics in the environment.

Persistent organic pollutants (POPs) have adverse effects on the human health and ecosystem functioning. Graphene oxide (GO) has been developed to remove trace levels of POPs from wastewater samples. However, many questions involved in these processes are still unresolved (e.g., the role of π–π interaction, the effect of GO on the degradation of POPs, and so on). Revealing the microscopic interactions between GO and POPs is of benefit to resolve these questions. In the present study, a quantum chemical calculation was used to calculate the molecular doping and adsorption energy between eight representative POPs and GO. The influences of GO on the thermodynamic parameters, such as the Gibbs free energy and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, were also reported. We found the molecular doping is dependent on the species of POPs. The adsorption energy of the majority of POPs on GO is between 7 and 8 kJ/mol. Consequently, the GO may make degradation of POPs in wastewater more productive and lead to a change of kinetics of the degradation of POPs.