Phenanthrene sorption in expanded polystyrene microplastics and environmental aging effects: A Venezuelan caribbean...

This study examined the sorption and desorption capacities of both new and environmentally aged expanded polystyrene microplastics regarding phenanthrene, a low-molecular-weight polycyclic aromatic hydrocarbon. The experimental procedures to evaluate sorption and desorption encompassed batch-reactor tests, mechanical stirring, and ultrasonication in aqueous phenanthrene solutions in contact with polymer beads, subsequently analyzed using High-Performance Liquid Chromatography. The results demonstrated that equilibrium was achieved at 720 min and the new expanded polystyrene followed the Freundlich isotherm model (R² = 0.962). Moreover, sorption parameters such as a nonlinearity index (N < 1) and a Freundlich constant (Kf = 7.425), derived for the new expanded polystyrene, indicate a heterogeneous substrate where sorption capacity increases concomitantly with rising analyte concentrations in the medium. Conversely, the aged polystyrene moderately fit the Dubinin-Radushkevich model (R² = 0.85). These findings, together with the kinetic analysis, indicated that, in both instances, the sorption rate was limited by both partition and pore-filling. Nevertheless, the aged expanded polystyrene absorbed 11% more phenanthrene than the new polystyrene. Furthermore, both new and aged expanded polystyrene demonstrated low phenanthrene desorption percentages, with values of 2 % and 3%, respectively. This low desorption implies that expanded polystyrene could serve as a long-term vector of non-polar organic pollutants in natural environments, which is attributed to desorption hysteresis.