Characterization of single and mixed microplastics in environmental matrices using Rock-Eval® pyrolysis

Microplastics (MPs) are widespread environmental contaminants, but their rapid detection and characterization in complex matrices remain challenging. This study evaluated Rock-Eval pyrolysis as a rapid screening and semiquantitative technique for polyethylene (PE), polypropylene (PP), and polystyrene (PS) in sand, soil, and river sediment. Individual polymers were spiked into each matrix at 0.5-4 wt%, while binary (PE + PP) and ternary (PE + PP + PS) mixtures were prepared to simulate the thermal behavior of mixed polymers. Responses were evaluated using Total HC, T_max, T10, T90, thermal degradation interval (ΔT), hydrogen index (HI), and oxygen index (OI). Total HC increased systematically with polymer loading, with R² > 0.90 for all the polymer-matrix combinations except PS in soil. Replicate analyses at 2 wt% produced average RSDs of 11.66% for total HC and 0.40% for T_max, providing an initial assessment of repeatability. PE and PP exhibited more matrix-dependent T_max values, whereas PS maintained a comparatively stable T_max of 396 °C-403 °C. Soil produced lower peak temperatures, broader hydrocarbon-release intervals, lower hydrogen indices, and higher oxygen indices than sand, reflecting contributions from indigenous organic matter. Sediments also broadened the PE and PP thermal profiles. Binary and ternary mixtures generated total HC responses approximately 23% and 72% higher, respectively, than composition-weighted values derived from the individual polymers. The ternary mixture also exhibited a broader, partially resolved bimodal S2 profile, indicating increased thermal complexity and potential non-additive behavior. These results demonstrate the proof-of-concept potential of Rock-Eval® pyrolysis for rapid MP screening and characterization while highlighting the importance of matrix and mixed-polymer effects.