The effects of sediment properties on the aeolian abrasion and surface characteristics of microplastics

Microplastics (<5 mm diameter) are significant environmental contaminants whose small sizes and low densities facilitate transport by wind. Transport by wind erosion alongside soils or sediments results in mechanical abrasion of the plastic surfaces which can alter their physical and chemical properties. This paper uses laboratory simulations to determine the effects of up to 216 hours of aeolian abrasion on polyethylene microplastics by angular, subrounded and rounded mineral sediments. During the abrasion process the mineral particles break down producing small fragments which adhere to the microplastic surfaces altering their surface roughness and chemistry. With increasing duration of abrasion the microplastic surface becomes coated with mineral fragments changing the dominant surface element from carbon to oxygen and silicon reflecting the composition of the erodents. The coating develops more rapidly when microplastics are abraded with angular sediments as these produce a lot of small fragments within the first 1-2 hours. However, after >200 hours of abrasion all the erodents had similar effects. A conceptual model of microplastic surface change is presented in which the plastic cracks and fractures, then flattens alongside the increasing density of sediment fragment cover. Surface changes may affect the ability of the plastics to transport airborne contaminants.