Combined Effects of UV Exposure Duration and Mechanical Abrasion on Microplastic Fragmentation by Polymer Type

TLDR

Fragmentation of plastic litter drives microplastic production in marine environments, yet the underlying processes remain poorly quantified. The study used laboratory accelerated weathering, exposing low‑density polyethylene, polypropylene, and expanded polystyrene to up to 12 months of UV followed by 2 months of sand abrasion to mimic beach conditions. UV exposure markedly increased fragmentation, especially for PP (≈6 k particles/pellet after 12 months) versus PE (≈20), while EPS fragments were dominated by abrasion alone (≈4 k particles/pellet) and grew to ≈12 k particles after 6 months UV plus abrasion, with fragmentation scaling inversely with size and up to 76 % of EPS volume lost to sub‑micron particles.

Abstract

It is important to understand the fragmentation processes and mechanisms of plastic litter to predict microplastic production in the marine environment. In this study, accelerated weathering experiments were performed in the laboratory, with ultraviolet (UV) exposure for up to 12 months followed by mechanical abrasion (MA) with sand for 2 months. Fragmentation of low-density polyethylene (PE), polypropylene (PP), and expanded polystyrene (EPS) was evaluated under conditions that simulated a beach environment. PE and PP were minimally fragmented by MA without photooxidation by UV (8.7 ± 2.5 and 10.7 ± 0.7 particles/pellet, respectively). The rate of fragmentation by UV exposure duration increased more for PP than PE. A 12-month UV exposure and 2-month MA of PP and PE produced 6084 ± 1061 and 20 ± 8.3 particles/pellet, respectively. EPS pellets were susceptible to MA alone (4220 ± 33 particles/pellet), while the combination of 6 months of UV exposure followed by 2 months of MA produced 12,152 ± 3276 particles/pellet. The number of fragmented polymer particles produced by UV exposure and mechanical abrasion increased with decreasing size in all polymer types. The size-normalized abundance of the fragmented PE, PP, and EPS particles according to particle size after UV exposure and MA was predictable. Up to 76.5% of the initial EPS volume was unaccounted for in the final volume of pellet produced particle fragments, indicating that a large proportion of the particles had fragmented into undetectable submicron particles.