The world-wide plastic production is literally exploded in the last fifty years, and more than half of the produced plastic is discarded in the environment. The rivers are the main vectors of the microplastic particles towards the oceans. This phenomenon is causing a variety of environmental impacts due to the degradation of plastic particle in the aquatic habitat (weathering, fragmentation, biofouling, etc.), also affecting the quantity of plastic transported and delivered to oceans. Moreover, plastic particles have different characteristics than fluvial sediment: for these reasons the transport processes of these particles in rivers are not known and need to be deeply investigated. The focus of this work is mainly on the settling velocity of plast.