A comparative investigation of the sorption of polycyclic aromatic hydrocarbons to various polydisperse micro- and nanoplastics using a novel third-phase partition method

Abstract

Evidence for direct adverse effects of micro- and nanoplastic particles (MNPs) on human health is scarce, but it has been hypothesized that MNPs act as carriers for environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs). Many studies have already investigated the sorption of PAHs to microplastics, typically using the batch-equilibrium method. Here we established a novel third-phase partition (TPP) method utilizing thermo-extractable polydimethylsiloxane-coated stir-bars as re-usable passive samplers to compare the sorption of PAHs to 17 different MNPs. This method facilitates the quantification of MNP-sorbed pollutants, including those with poor water-solubility without requiring laborious filtration and solvent-extraction steps. Using benzo[a]pyrene (B[a]P) as a representative PAH, sorption kinetics and isotherms for MNPs were evaluated. B[a]P sorption was generally strong but differed by over two-orders of magnitude, clustering according to polymer types in the order of polyamides > polyethylenes ≫ Tire Rubber > polyurethanes > polymethyl methacrylate. B[a]P sorption was diminished for photo-aged MNPs. Within given polymer types, properties including particle size, polarity/hydrophobicity and chain mobility notably influenced B[a]P sorption. When comparing different PAHs, their sorption to selected MNPs increased over five-orders of magnitude with hydrophobicity: anthracene < B[a]P < dibenzo[a,l]pyrene. Our data is an important contribution to the understanding of the sorption behaviors of MNPs. The novel TPP-method represents a universally-applicable approach for the reliable evaluation of sorption characteristics of contaminants and MNPs, and can be easily adapted to desorption studies.