Transport and deposition of micro-plastic particles in rivers

Luca Solari

Rivers represent the main pathways for transport of plastic to the open sea. In rivers, plastic debris can be transported either as floating or submerged matter. While floating plastic can be easily detected, it can represent a negligible fraction of the total plastic waste load as a great portion of plastic debris is unseen while flowing submerged in the water column or even accumulating in the river bed. The knowledge of transport and deposition processes in river basins is fundamental for a reliable evaluation of the amount of plastics annually delivered to the sea 
Mobility of plastics is driven by hydraulic processes provided its basic physical properties (size, shape and density). While the entrainment, transport and deposition of natural sediment particles have been extensively studied in various hydraulics and sedimentary settings, the extension of these fundamental studies to plastic particles is not trivial. 
In this presentation, the focus is on the interpretation, through analytical and laboratory analyses, on some fundamental mechanisms governing the deposition and accumulation of Micro-Plastic particles in rivers such as: MP settling velocity, MP infiltration into sediment bed, MP incipient motion. Results indicate that existing knowledge of natural sediment transport cannot be directly applied to the interpretation of MP transport.