Sorption Behavior of Trace Organic Chemicals on Carboxylated Polystyrene Nanoplastics

Nanoplastics possess unique characteristics (e.g., high surface area/volume ratio) that enhance the adsorption of organic chemicals onto their surface. Their occurrence raises human health and ecotoxicological concerns, as pollutants bound to nanoplastics can have a larger effect than they would on their own. This study assessed the sorption of plant protection products (glyphosate and methyl parathion), an antidepressant (fluoxetine), a perfluorochemical (perfluorooctanoic acid [PFOA]), and a polycyclic aromatic hydrocarbon (phenanthrene) onto commercially available carboxylated polystyrene (PS) nanoplastics (NPs, 500 and 20 nm). Based on the calculated sorption coefficients (K_d, L/kg), the sequence of chemicals displaying the highest to lowest affinity toward PSNPs is fluoxetine > phenanthrene > methyl parathion > PFOA > glyphosate, with 20 nm PS showing a higher potential to sorb organic chemicals. Cationic (fluoxetine) and hydrophobic (phenanthrene) substances were more amenable to sorption, whereas negatively charged and more hydrophilic ones (i.e., PFOA and glyphosate) showed poor sorption. pH influenced sorption for all target chemicals except phenanthrene. Sorption capacity was further reduced in water spiked with natural organic matter and in tertiary-treated wastewater effluent. Overall, our work enhances the understanding of how representative organic chemicals sorb onto nanoplastics and provides quantitative information (i.e., K_d) on future simulations of nanoplastics’ fate and transport.