Sorption of non-ionic organic compounds by polystyrene in water

Polystyrene (PS) is a plastic material that is well known for its use in many different applications, e.g. as shock sensitive packaging. With its prevalence across society, PS contributes significantly to the overall plastic load in aqueous systems. Sorption of organic compounds by the plastics, especially micrometer-sized particles, in the environment has become a concern in the past years. The aim of this study was to improve the understanding of sorption properties of PS, one of the major plastic pollutants in the aqueous environment. Batch experiments with PS film (29 μm thickness) were performed for 4 days using a diverse set of 24 sorbates to account for varying molecular properties like polarity or molecular volume. Isotherms were evaluated using different sorption models to elucidate the sorption process of PS. Sorption to PS film was non-linear and absorption into the bulk material was the dominant sorption mode. A clear discrimination between the specific and non-specific interactions in the aqueous environment could be shown. The non-linear sorption to PS was shown to be controlled by the molar volume but also by the polarizability/dipolarity parameter (S) of the ppLFER model. The latter is influenced by the aromatic π-π-interactions of PS with the sorbate. Similar to other plastics like polyethylene, sorption to PS is driven by hydrophobic interactions but phase descriptors of pristine PS were significantly different than descriptors for other environmental relevant plastics.