Post COVID-19 pandemic: Disposable face masks as a potential vector of antibiotics in freshwater and seawater.

With the outbreak and widespread of the COVID-19 pandemic, large numbers of disposable face masks (DFMs) were abandoned in the environment. This study first investigated the sorption and desorption behaviors of four antibiotics (tetracycline (TC), ciprofloxacin (CIP), sulfamethoxazole (SMX), and triclosan (TCS)) on DFMs in the freshwater and seawater. It was found that the antibiotics in the freshwater exhibited relatively higher sorption and desorption capacities on the DFMs than those in the seawater. Here the antibiotics sorption processes were greatly related to their zwitterion species while the effect of salinity on the sorption processes was negligible. However, the desorption processes were jointly dominated by solution pH and salinity, with greater desorption capacities at lower pH values and salinity. Interestingly, we found that the distribution coefficient (Kd) of TCS (0.3947 L/g) and SMX (0.0399 L/g) on DFMs was higher than those on some microplastics in freshwater systems. The sorption affinity of the antibiotics onto the DFMs followed the order of TCS > SMX > CIP > TC, which was positively correlated with octanol-water partition coefficient (log Kow) of the antibiotics. Besides, the sorption processes of the antibiotics onto the DFMs were mainly predominated by film diffusion and partitioning mechanism. Overall, hydrophobic interaction regulated the antibiotics sorption processes. These findings would help to evaluate the environmental behavior of DFMs and to provide the analytical framework of their role in the transport of other pollutants.

Enhanced heavy metal adsorption on microplastics by incorporating flame retardant hexabromocyclododecanes: Mechanisms and potential migration risks.

Microplastics (MPs) are known to act as carriers of heavy metals; however, little is known about the intrinsic chemical additives of MPs, such as hexabromocyclododecane (HBCD), in terms of the adsorption behaviors and migration risks of heavy metals on MPs. Here, we reported the potential mechanisms and risks of HBCD inherent in polystyrene (PS) MPs with Cu(II), Ni(II), and Zn(II) adsorption/desorption. A comparison of the adsorption capacity of the metals onto HBCD/PS composites (HBCD/PS) MPs (10.31-20.76 µmol/g), pure MPs (0-3.60 µmol/g), and natural minerals (0.11-13.88 µmol/g) showed that the addition of HBCD significantly promoted the metals adsorption onto the HBCD/PS MPs, and even exceeded that of natural particles. Isotherms and thermodynamic data suggested that the adsorption process of the metals onto the HBCD/PS MPs was spontaneous and endothermic, and that the adsorption was a mainly multi-ion process with an inclined direction. Furthermore, the results of SEM-EDS, FTIR, and XPS analyses, as well as density functional theory well explained that the metals were mainly adsorbed on the -O and -Br groups of the HBCD/PS MPs via electrostatic interactions and surface complexation. More importantly, by comparing the desorption activity with natural river water and seawater, HBCD inherent in MPs can enhance the long-range transfer of metals carried by the HBCD/PS MPs from contamination sources to potential sink like oceans. Thus, the HBCD/PS MPs with high loading of Cu(II), Ni(II), and Zn(II) could be potential secondary sources of these metals in seawater. Overall, these findings revealed the potential risks of flame retardant in MPs associated with metal migration, and advocated that flame retardant-related waste MPs should be included in coastal sustainable development.

Sorption of tetracycline onto hexabromocyclododecane/polystyrene composite and polystyrene microplastics: Statistical physics models, influencing factors, and interaction mechanisms.

Microplastics (MPs) are becoming a major concern due to their great potential to sorb and transport pollutants in the aquatic environment; hexabromocyclododecane (HBCD) is a common chemical additive in polystyrene (PS) MPs. However, the underlying mechanisms for the interaction of tetracycline (TC) onto HBCD-PS composites MPs (HBCD-PS MPs) are still not well documented. Our findings showed that the addition of HBCD resulted in a relatively higher hydrophobicity of PS MPs, and significantly enhanced the sorption ability of HBCD-PS MPs for TC. The kinetic models suggested that the sorption of TC onto PS and HBCD-PS MPs were mainly controlled by film diffusion and intra-particle diffusion, respectively. The statistical physics models were used to elucidate the sorption of TC onto PS and HBCD-PS MPs was associated with the formation of the monolayer, and the results indicated the TC was sorbed onto the two MPs by both multi-molecular and non-parallel processes. The TC sorption was solution pH-dependent while the effect of NaCl content on TC sorption was negligible. The presence of Cu(Ⅱ), Pb(Ⅱ), Cd(Ⅱ), and Zn(Ⅱ) ions had different influences on the TC sorption onto both the MPs. Overall, various mechanisms including π-π and hydrophobic interactions jointly regulated the sorption of TC onto both the MPs. Our results provided new insights into the sorption behavior and interaction mechanisms of TC onto both the MPs and highlighted that the addition of HBCD likely increased the enrichment capacity of MPs for pollutants in the environment.

Adsorption of fulvic acid onto polyamide 6 microplastics: Influencing factors, kinetics modeling, site energy distribution and interaction mechanisms.

Information on the interactions of microplastics (MPs) with dissolved organic matter (DOM) is essential for understanding their environmental impacts. This study selected fulvic acid (FA) as a typical DOM to investigate the influence of contact time, temperature, dosage, solution pH, salinity, and coexisting metal ions on the adsorption of FA onto polyamide 6 (PA6) MPs. The adsorption kinetic and isotherm can be successfully described by mixed-order (MO) and Freundlich models. The adsorption site energy distribution based on the Freundlich equation was applied to analyze the interaction between FA and PA6-MPs and the adsorption site heterogeneity. Thermodynamic analysis demonstrated that the values of parameters (ΔGads°, ΔSads°, ΔHads°) were significantly affected by initial solution concentrations and the adsorption process was spontaneous, endothermic, and randomness-increased. Fourier transform-infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed the importance of amide functional groups of PA6-MPs in controlling FA adsorption. Hydrogen bonds, hydrophobic, electrostatic, and n-π electron donor-acceptor (n-π EDA) interactions played different roles on adsorption of FA under different conditions of solution chemistry. These findings are beneficial to provide new insights involving the adsorption behavior and interaction mechanisms of FA onto PA6-MPs for the environmental risk assessment of MPs.

Hexabromocyclododecane alters malachite green and lead(II) adsorption behaviors onto polystyrene microplastics: Interaction mechanism and competitive effect.

The role of microplastics (MPs) as a carrier of pollutants in water environment is an emerging issue; however, information regarding the underlying mechanisms for malachite green (MG) and Pb(II) adsorption onto hexabromocyclododecane (HBCD)-polystyrene (PS) composites MPs (HBCD-PS MPs) is still lacking. In this study, the adsorption behaviors and mechanisms of MG and Pb(II) onto PS and HBCD-PS MPs were investigated in batch adsorption experiments. The amounts of MG and Pb(II) adsorbed onto PS MPs were negligible while the presence of HBCD significantly enhanced the adsorption of MG and Pb(II) onto HBCD-PS MPs. The results of intra-particle and film diffusion model confirmed that the adsorption of MG and Pb(II) onto HBCD-PS MPs was dominated by intra-particle diffusion. The maximum adsorption amount (qm) of Pb(II) and MG onto HBCD-PS MPs followed the sequence of Pb(II) (3.33 µmol g-1) > MG (1.87 µmol g-1). In binary systems, MG and Pb(II) showed competitive adsorption onto HBCD-PS MPs, and Pb(II) exhibited relatively higher affinity to be adsorbed onto HBCD-PS MPs. Solution pH and salinity played a crucial role in the adsorption process. XPS analysis suggested that the -Br participated in the adsorption process as an electron-withdrawing group. Overall, electrostatic interaction regulated the adsorption of MG and Pb(II) onto HBCD-PS MPs. Results from this study demonstrated that HBCD could enhance the role of MPs in the MG and Pb(II) migration by changing their adsorption behavior onto MPs.