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 the relevant time and length scales. Here, we employ microsecond coarse-grained molecular dynamics simulations with the Martini 3 force field, using humic substances (HSs) as SOM representatives. We pursued two complementary modeling perspectives: (i) comparing the behavior of polyethylene oxide (PEO) and polyethylene (PE) chains within SOM matrices, and (ii) examining SOM association with a PE nanoparticle across varying pH. 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, low pH promoted dispersion of HS aggregates and enhanced surface coverage of the plastic particle. Together, these results provide molecular-scale insights into how polymer polarity, SOM composition, and environmental pH govern NP–SOM interactions.