Alkaline cementitious matrix effects on the fate of per- and polyfluoroalkyl substances (PFAS) in recycled plastic aggregates

Recycled plastics, including polyethylene terephthalate (rPET) and high-density polyethylene (rHDPE), are increasingly used as construction materials in response to sustainability and circular-economy goals, to repurpose waste streams and reduce natural-resource demand. This study provides the first assessment of PFAS adsorption by recycled plastic aggregates (rPA) and subsequent desorption in simulated cement pore solution (SCPS) by evaluating sorption-desorption mechanisms as functions of polymer type, surface chemistry, exposure duration, and perfluoroalkyl chain length (C4-C11). Batch experiments quantified indicative multi-analyte PFAS loading under neutral pH and PFAS desorption under construction-relevant exposure to high pH (>12.5) and ionic strength (0.85-1.0 M) SCPS. PFAS with carbon chain lengths >C8 showed strong adsorption affinity for rHDPE over rPET (6.2-106.5% greater mass-normalised adsorption (pg/g)), with competitive uptake increasing with chain length and contact time up to 28 days. Desorption into near-neutral ultrapure water was negligible (<LOD), confirming rPA as effective short-term sinks for PFAS. However, SCPS induced substantial PFAS desorption from rPA, particularly of short-chain perfluorobutanoic acid (PFBA) from rPET, and (less so) rHDPE. These findings challenge the long-term viability of rPA in concrete, highlight their potential as transient PFAS sinks or enduring leaching sources, and emphasise the need for risk-based guidelines for rPA use in cementitious matrices.