Novel Release Mechanism of Microplastics and Nanoplastics by Environmentally Relevant Sand Abrasion

Mechanical degradation of plastics is a major source of micro- and nanoplastics (MPs/NPs) released into natural environments. However, our understanding of this process remains limited, and methods to quantify the mechanical degradation intensity are lacking. We designed a quantitative device to study MP/NP release arising strictly from surface abrasion of low-density polyethylene (LDPE) films by freely sliding/rolling dry sand over 7 months. We characterized the dynamic changes in released products, polymer surface, and sand surface, and correlated the release rates with input power from sliding friction. Environmentally relevant sand surface abrasion alone released only NPs (<400 nm, suspended) and water-extracted dissolved organic carbon (2-44 μg PE/cm²). Beyond suspended debris, we discovered that MPs/NPs' (sub- to low-micron) can transfer onto sand grains- a novel and major release mechanism that could serve as a new source of MPs/NPs. Simultaneously, a dynamic layer of sand minerals was deposited on LDPE. Such mutual transfer is hypothesized to be stochastic and to interfere with the subsequent MP/NP release. Our findings highlight that MP/NP release and fate from environmentally relevant sand abrasion are more complex than our previous understanding. Correlating the input power with harmonized degradation rates indicated that solid abrasion releases debris more efficiently than fluid shear.