Transport of polystyrene nanoplastics in porous media: Combined effects of two co-existing substances

Surfactant-mediated transport of polyvinyl chloride nanoplastics in porous media: Influence of natural organic matter, natural inorganic ligands and electrolytes

This study investigates the transport behavior of polyvinyl chloride nanoplastics (PVC-NPs) in porous media under surfactant-mediated conditions through a combination of column experiments, numerical simulations, and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) interaction energy analysis. The effects of different surfactant types, ionic species, ionic strength, humic acid (HA), and phosphate were examined. Results indicate that surfactants enhance the transport of PVC-NPs, with anionic surfactants exhibiting a stronger enhancement effect than cationic ones. Generally, the addition of cations inhibited PVC-NPs transport, with divalent Ca2+ exhibiting a stronger inhibitory effect than monovalent Na+. Interestingly, at low ionic strengths, Na+ had a stronger inhibitory effect than Ca2+. In the presence of anionic surfactants, higher Na+ concentrations promoted PVC-NPs transport. In contrast, both HA and phosphate inhibited PVC-NPs transport under cationic surfactants, with the degree of inhibition positively correlated with their concentrations. However, under anionic surfactants, high concentrations of HA inhibited PVC-NPs transport, while lower concentrations had no significant impact. Phosphate, under anionic surfactant conditions, initially inhibited but subsequently promoted PVC-NPs transport. This study provides a comprehensive understanding of the natural transport and transformation mechanisms of PVC-NPs in the environment under surfactant influence, offering a solid data foundation and theoretical framework for accurately assessing the potential ecological and human health risks posed by nanomaterials.

Effect of carbon chain length and concentration of perfluorinated compounds on polytetrafluoroethylene microplastics transport behavior

Perfluorooctanoic acid (PFOA) and perfluoropentanoic acid (PFPeA), as important components of perfluorinated compounds (PFAS), are not only ecologically hazardous, but also have surfactant properties that can alter the transport behavior of polytetrafluoroethylene (PTFE) in porous media. In this experiment, the effect of PFAS on the transport of PTFE in porous media under different pH, ionic strength (IS) and ion valence states was studied. The results showed that the recovery rate of PTFE decreased gradually with the decrease of pH and the increase of IS and ion valence states. When the above conditions change, the double electron layer on the microplastic surface is compressed, the absolute value of zeta potential decreases, the repulsion between each other decreases, and aggregation and deposition are more likely. In addition, it was found that the recovery rate of PTFE co-transported with long chain PFOA was higher than that of short chain PFPeA. This phenomenon may be caused by the adhesion ability of PFOA with long carbon chain on the surface of PTFE is greater than that of PFPeA with short carbon chain. On the other hand, PFAS with different carbon chain lengths produce different spatial site resistance effects after binding with particles, and the spatial site resistance produced by the long-chain PFOA is larger than that of the short-chain PFPeA, leading to a decrease in particle-to-particle aggregation and a better transport effect. This study will help to understand the effects of PFAS with different carbon chain lengths on the transport of microplastics in porous media, as well as the transport rule of PTFE under different conditions, and provide reference value for the calculation of its flux in soil.

Cotransport of 6PPD-Q and pristine/aged microplastics in porous media: An insight based on transport forms and mechanisms

The environmental fate and risks of microplastics (MPs) and their associated contaminants have attracted increasing concern in recent years. In this study, the cotransport of six kinds of pristine and aged MPs and the antiager ozonation product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) were investigated via a series of batch and transport experiments, and characteristic analysis (e.g., SEM, FTIR and XPS). Generally, pristine MPs exhibit higher adsorption ability than aged MPs due to the hydrophobic interaction. The 6PPD-Q usually exhibited both free moving and bond-MPs moving during transport process in presence of MPs, but none free 6PPD-Q was detected in presence of pristine PP MPs. The mobility of 6PPD-Q was generally facilitated in presence of MPs by bond-MPs moving due to the hydrogen bonding, halogen bonding, π-π interaction (the maximum total mass recovery of 84.11%), which efficiency was influenced with the combined effect of adsorption ability and mobility of MPs. The pristine PVC MPs showed highest facilitation on 6PPD-Q transport. The retained 6PPD-Q in porous media also was released by various MPs with different mass recovery ranged from 15.72% to 56.26% via surface moving of MPs around porous media. Both the dissolved and retained 6PPD-Q decreased the MPs mobility with the minimum mass recovery of 34.02%. Findings from this study contribute to the prediction and assessment of the combined risks of MPs and 6PPD-Q.

Cu(II) inhibited the transport of tetracycline in porous media: role of complexation

Tetracycline (TC) and Cu(II) coexist commonly in various waters, which may infiltrate into the subterranean environment through runoff and leaching, resulting in substantial ecological risks. However, the underlying mechanisms why Cu(II) affects the transport of TC in porous media remain to be further explored and supported by more evidence, especially the role of complexation. In this study, the transport of TC with coexisting Cu(II) was comprehensively explored with column experiments and density functional theory (DFT) calculation. At natural environmental concentrations, Cu(II) significantly inhibited the transport of TC in the quartz sand column. Cu(II) augmented the retention of TC in the column mainly via electrostatic force and complexation. The interaction between TC and TC-Cu complexes on the surface of SiO2 was investigated with first-principles calculations for the first time. There were strong van der Waals forces and coordination bonds on the surface of complexes and SiO2, leading to higher adsorption energy than that of TC and inhibiting its penetration. This study offers novel insights and theoretical framework for the transport of antibiotics in the presence of metal ions to better understand the fate of antibiotics in nature.

The long-term release and particle fracture behaviors of nanoplastics retained in porous media: Effects of surfactants, natural organic matters, antibiotics, and bacteria

The transport of nanoplastics (NPs) in porous media has received a lot of attention, but the studies on the long-term release of NPs retained in porous media and the particle fracture during this process are seriously lacking. For filling this deficiency, we examined the individual or synergistic effects of surfactants, natural organic matters (NOMs), antibiotics, and bacteria on the desorption, long-term release, and particle fracture behaviors of polystyrene NPs (PS-NPs) retained in porous media. It was found that the change in hydrophilicity of PS-NPs dominated the long-term release of PS-NPs retained in porous media when surfactants were present. In the single system of surfactants and the dual system of surfactants and NOMs, the release of PS-NPs were improved owing to the increasing hydrophilicity of PS-NPs, although cationic surfactants also reduced the electrostatic repulsion between PS-NPs and porous media. Increasing antibiotic concentration reduced the electrostatic repulsion between PS-NPs and porous media to inhibit the release of PS-NPs. When bacteria were present whether containing antibiotics or not, the effects on roughness of PS-NPs dominated the release of PS-NPs. The effects of surfactants and NOMs on the PS-NP desorption were similar with the long-term release, with changes in hydrophilicity dominating the process. Whereas the effects of antibiotics and bacteria on the PS-NP desorption were different with the long-term release. Surfactants and NOMs in the presence of surfactants inhibited the fracture of PS-NPs by increasing the hydrophilicity of PS-NPs brought about the coating of water molecules on PS-NPs for protection. Antibiotics had no significant effects on the fracture of PS-NPs due to unaltered vertical forces on PS-NPs and no protective effect. Bacteria in the presence or absence of antibiotics inhibited the fracture of PS-NPs by coating PS-NPs retained in porous media to protect PS-NPs from fracture.

Statuses, shortcomings, and outlooks in studying the fate of nanoplastics and engineered nanoparticles in porous media respectively and borrowable sections from engineered nanoparticles for nanoplastics

This review discussed the research statuses, shortcomings, and outlooks for the fate of nanoplastics (NPs) and engineered nanoparticles (ENPs) in porous media and borrowable sections from ENPs for NPs. Firstly, the most important section was that we reviewed the research statuses on the fate of NPs in porous media and the main influencing factors, and explained the influencing mechanisms. Secondly, in order to give NPs a reference of research ideas and influence mechanisms, we also reviewed the research statuses on the fate of ENPs in porous media and the factors and mechanisms influencing the fate. The main mechanisms affecting the transport of ENPs were summarized (Retention or transport modes: advection, diffusion, dispersion, deposition, adsorption, blocking, ripening, and straining; Main forces and actions: Brownian motion, gravity, electrostatic forces, van der Waals forces, hydration, filtration, bridging; Affecting elements of the forces and actions: the ENP and media grain surface functional groups, size, shape, zeta potential, density, hydrophobicity, and roughness). Instead of using the findings of ENPs, thorough study on NPs was required because NPs and ENPs differed greatly. Based on the limited existing studies on the NP transport in porous media, we found that although the conclusions of ENPs could not be applied to NPs, most of the influencing mechanisms summarized from ENPs were applicable to NPs. Combining the research thoughts of ENPs, the research statuses of NPs, and some of our experiences and reflections, we reviewed the shortcomings of the current studies on the NP fate in porous media as well as the outlooks of future research. This review is very meaningful for clarifying the research statuses and influence mechanisms for the NP fate in porous media, as well as providing a great deal of inspiration for future research directions about the NP fate in porous media.