Influence of shape on the incipient motion of exposed microplastics

AbstractMicroplastics are now widely detected in aquatic environments, with rivers serving as key transport pathways from land to the ocean. Understanding the incipient motion thresholds of microplastic is essential for predicting their transport dynamics in water bodies. Upon entering the environment, microplastics undergo aging processes that alter their physical and chemical properties, yet existing models for predicting incipient motion thresholds do not account for these effects. This study determines the critical flow velocity for aged microplastics and assesses the influence of aging and shape factors on their mobilization using both experimental data from the literature and new experiments. To incorporate particle shape effects, the repose angle and drag coefficient of microplastics were considered. A new explicit formula was developed to directly calculate incipient motion thresholds for both aged and unaged microplastics, achieving a relative average error of 12.1%, which outperforms existing models.