Interactions between Submicron Carbon Particles, Escherichia coli and Humic acid with Plastic Surfaces

Plastic materials are widely used in engineered systems and increasingly accumulate in natural environments, where their surfaces interact with colloids, microorganisms, and dissolved organic matter. However, the relative roles of plastic surface properties versus particle-specific characteristics in governing organic matter retention remain poorly constrained. Here, attachment efficiency () was used to quantify intrinsic particle-collector affinity on three common thermoplastics (ABS, HDPE, HIPS) and glass beads as an inorganic reference. Surface chemistry, hydrophobicity, roughness, and charge were characterized, and interactions with submicron carbon particles (SCPs) and Escherichia coli were evaluated using column experiments. Extended DLVO (XDLVO) theory was applied to predict interaction energy barriers, and humic acid (HA) adsorption was quantified through batch isotherms. XDLVO modeling predicted higher affinity of particles for plastics relative to glass; however, experimentally measured attachment efficiencies were uniformly low ( < 0.05) across all materials. Attachment was primarily governed by particle size and surface charge rather than collector hydrophobicity, roughness, or surface chemistry. SCP consistently exhibited higher than bacteria, while differences among plastics were minor. Similarly, HA adsorption was weak and near-linear, with uptake following ABS {approx} HIPS > HDPE > glass, indicating reversible, partitioning-like association dominated by polymer-specific functionality rather than electrostatics. The absence of correlation between and XDLVO-predicted energy barriers further demonstrates limitations of classical physicochemical models in describing particle- plastic interactions. Collectively, these results indicate that pristine thermoplastic surfaces exhibit intrinsically low affinity for organic matter and that particle-specific properties dominate retention under low ionic strength conditions. Enhanced accumulation in environmental systems likely requires surface aging or conditioning processes not captured by classical interaction theory.