Coarse-Grained Simulations of the Nanoplastic Interaction with Soil Organic Matter

Nanoplastics (NPs) in terrestrial ecosystems represent an emerging ecological threat, yet their molecular-level interactions with soil organic matter (SOM) remain difficult to probe experimentally. Molecular simulations can bridge this gap if they capture relevant time and length scales. Here, microsecond coarse-grained molecular dynamics simulations were employed with the Martini 3 force field using humic substances (HSs) as SOM representatives. We pursued two complementary modeling perspectives: (i) comparing the behavior of poly(ethylene oxide) (PEO) and polyethylene (PE) chains within SOM matrices and (ii) examining SOM association with a PE nanoparticle across varying pH values. PEO exhibited strong hydration and high mobility, whereas PE interacted weakly with acidic moieties but bound strongly to hydrophobic groups under low-acidity conditions, leading to reduced diffusivity. In the PE nanoparticle simulations, a low pH promoted dispersion of HS aggregates and enhanced surface coverage of the plastic particle. Together, these results provide molecular-scale insights into how the polymer polarity, SOM composition, and environmental pH govern NP-SOM interactions.