Settling velocity of microplastic particles of regular shapes

Abstract

Terminal settling velocity of around 600 microplastic particles, ranging from 0.5 to 5mm, of three regular shapes was measured in a series of sink experiments: Polycaprolactone (material density 1131kgm−3) spheres and short cylinders with equal dimensions, and long cylinders cut from fishing lines (1130–1168kgm−3) of different diameters (0.15–0.71mm). Settling velocities ranging from 5 to 127mms−1 were compared with several semi-empirical predictions developed for natural sediments showing reasonable consistency with observations except for the case of long cylinders, for which the new approximation is proposed. The effect of particle's shape on its settling velocity is highlighted, indicating the need of further experiments with real marine microplastics of different shapes and the necessity of the development of reasonable parameterization of microplastics settling for proper modeling of their transport in the water column.