Does crack morphology govern PFAS sorption in landfilled plastics?

Plastics in landfills undergo extensive aging and surface cracking, yet it remains unclear whether crack morphology governs the sorption of per- and polyfluoroalkyl substances (PFAS) under realistic landfill conditions. Thus, this study characterized 55 hard and 19 soft plastic samples collected from various landfill depths and investigated their comparative sorption of PFAS. Hard plastics, including HDPE, PP, PET, PS, and PVC, exhibited surface cracks classified into line, curve, and network patterns, with crack density increasing with landfill depth. In contrast, soft plastics (LDPE) showed no visible cracks regardless of depths, which was further confirmed by two-dimensional spectral analysis. PFAS extracted from plastics, following the EPA Method 1633, revealed significantly higher PFAS loads in LDPE plastics (45.9–309.9 µg/kg) than in hard plastics (1.7–16.8 µg/kg), despite higher crack density in hard plastics. Such a contrast indicates that partition-type sorption plays an important role in the retention of PFAS on plastics in landfills, and that soft plastics with high free volume are particularly important hotspots for PFAS accumulation. Crack density was not significantly correlated with PFAS sorbed on hard plastics, indicating that contaminant retention is governed by landfill-mediated processes beyond surface cracking. Quantitative analysis of adsorbed organic carbon on hard plastics demonstrates organic masking that limits direct PFAS–polymer interactions. Consequently, surface cracking plays a secondary or effectively masked role under realistic landfill conditions, refining mechanistic understanding of PFAS fate in engineered waste systems.