Distinguishing between Extractable and Leachable Contents of Styrene Oligomers in Various Polystyrene Consumer Products: Towards Environmentally Realistic Scenarios

Abstract

Plastic additives' environmental impacts remain insufficiently understood due to knowledge gaps in their bioavailability, despite growing concerns from increased plastic use and waste. Additives that are non-covalently bound but strongly interact with polymers can be extractable but not leachable, thus non-bioavailable. Nevertheless, most studies have not distinguished between extractable (EC) and leachable content (LC) in plastic additives. We quantified the EC and LC of styrene oligomers (SOs) in polystyrene (PS) by applying the selective solvent compatibility of PS—dissolution in dichloromethane for EC and swelling in n-hexane for LC. Significant differences were found between EC and LC of SOs in 28 widely consumed PS products and across three PS types—expanded PS (EPS), extruded PS (XPS), and solid PS. EPS showed lower EC and LC values and fewer SO isomers. LCs were only 32% (EPS), 84% (XPS), and 72% (solid PS) of ECs, suggesting bioavailable fractions may be overestimated if only EC is considered. We estimate that 3.3 MT of PS-incorporated SOs, with 76% in leachable forms, have entered the environment, but much may still remain in PS debris. Distinct isomer ratios and high non-leachable fractions in EPS suggest that SOs could serve as effective tracers for distinguishing and quantifying invisible EPS-origin particles in beach sediments. This study underscores the need to differentiate EC from LC for environmentally realistic risk assessment and source identification.