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Phenanthrene sorption in expanded polystyrene microplastics and environmental aging effects: A Venezuelan caribbean beaches case study
Summary
This study measured how well expanded polystyrene microplastics collected from Caribbean beaches in Venezuela absorb and hold phenanthrene, a toxic hydrocarbon found in oil and combustion exhaust. Environmentally aged polystyrene absorbed 11% more phenanthrene than fresh plastic, and once absorbed, both types released very little of it back into water — meaning polystyrene acts as a long-term reservoir for toxic organic compounds in marine environments. This "trojan horse" effect is a key concern for wildlife and potentially humans who consume seafood from polluted coastal areas.
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 (R = 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 (R = 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.
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