Adsorption of 2-hydroxynaphthalene, naphthalene, phenanthrene, and pyrene by polyvinyl chloride microplastics in water and their bioaccessibility under in vitro human gastrointestinal system.

The interaction of microplastics (MPs) and organic pollutants has recently become a focus of investigation. To understand how microplastic residues affect the migration of organic pollutants, it is necessary to examine the adsorption and desorption behavior of organic pollutants on MPs. In this study, integrated adsorption/desorption experiments and theoretical calculations were used to clarify the adsorption mechanism of 2-hydroxynaphthalene (2-OHN), naphthalene (NAP), phenanthrene (PHE), and pyrene (PYR) by polyvinyl chloride microplastics (PVC-MPs). Based on the phenomenological mathematical models, the rate-limiting step for analyte adsorption onto PVC-MPs was adsorption onto active sites (R2 = 0.865-0.995). Except for PHE, analyte adsorption isotherms were well described by the Freundlich model (R2 = 0.992-0.998), and adsorption thermodynamics showed that analyte adsorption on PVC-MPs was a spontaneous exothermic process (ΔH0 < 0; ΔG0 < 0). Based on the order of adsorption efficiency of 2-OHN < NAP < PHE < PYR, which is identical to the competitive adsorption experiment, polycyclic aromatic hydrocarbon (PAH) adsorption on PVC-MPs increased as the aromatic ring number increased and the hydroxyl content decreased. The release of 2-OHN (49 %-52 %) from PVC-MPs into the simulated gastrointestinal environment was greater than that of NAP (5.5 %-5.7 %). Theoretical calculations and adsorption tests indicated that hydrophobic interaction was the primary influence on the adsorption of PAHs and their hydroxylated derivatives by PVC-MPs. These findings improve our understanding of MPs' behavior and dangers as pollutant carriers in the aquatic environment and help us develop recommendations for the pollution control of MPs.

Effects of hydroxyl group content on adsorption and desorption of anthracene and anthrol by polyvinyl chloride microplastics.

Pollutant-attached microplastics have received increasing attention in recent years. However, information regarding the influence of hydroxyl group content of pollutants on the adsorption and desorption behavior is unclear, which affects their fate and risks in the aquatic environment. In this study, we investigated the adsorption and desorption behavior of anthracene (ANT) and its hydroxy derivatives (OHAs), including 2-hydroxyanthracene (MOHA), 2,6-dihydroxyanthracene (DOHA), and 1,8,9-trihydroxyanthracene (TOHA) on polyvinyl chloride (PVC) microplastics, and their interaction mechanism through the batch, characterization, and computational experiments. The results showed that the adsorption of ANT and OHAs on PVC microplastics conformed to the pseudo-second-order kinetic model and was exothermic spontaneously. The adsorption efficiency on PVC followed the order of ANT > MOHA > DOHA > TOHA, indicating that increase in hydroxyl group substitution degree will inhibit pollutant adsorption on PVC microplastics. Conversely, the release amounts of MOHA from PVC into simulated gastric fluids were higher than those of ANT. Experimental and computational results suggested that the affinity of ANT/OHAs to PVC microplastics was the most likely outcome in hydrophobic effect, electrostatic repulsion, and CH-π interaction forces. These findings help elucidate the mechanisms of pollutant adsorption on microplastics and evaluate the risk of pollutant-attached microplastics in the aquatic environment.

Adsorption of phenanthrene and its monohydroxy derivatives on polyvinyl chloride microplastics in aqueous solution: Model fitting and mechanism analysis.

The pervasiveness of microplastics, which can absorb pollutants, has a certain impact on pollutant migration in natural waters. Differences in functional groups, such as the hydroxyl group, of pollutants will affect their adsorption on microplastics. In this study, the adsorption of phenanthrene (PHE) or its monohydroxy derivatives, including 1-hydroxyphenanthrene (1-OHP), 2-hydroxyphenanthrene (2-OHP), 4-hydroxyphenanthrene (4-OHP), and 9-hydroxyphenanthrene (9-OHP), on polyvinyl chloride (PVC, measured mean particle size = 134 µm) microplastics was studied. The adsorption efficiency of PHE was shown to be higher than that of either of OHPs. A better fit for pseudo-second-order and Freundlich isotherm models was obtained, indicating different binding sites on the surface of PVC microplastics. The adsorption processes of PHE and OHPs on PVC microplastics were demonstrated to be exothermic and spontaneous. Combined with FT-IR analysis, theoretical calculation, and comparative adsorption experiments, hydrophobic interaction was the dominant mechanism during the adsorption process. In contrast, electrostatic repulsion, CH/π interaction, and halogen bonding played a minor role, to an extent, in the adsorption of PHE/OHPs on PVC microplastics. These findings indicate the influence of the hydroxyl group on adsorption and improve the understanding of interactions between PVC microplastics and PHE/OHPs.