Mirco Mancini

Microplastics (MPs) have been defined as plastic particles in a size range from 1 μm to 5 mm and several studies have shown that MPs can be found in oceans, on shores, in surface waters and in sediments around the world. The great variability of their physical and mechanical characteristics and the various shapes under which they can occur, make their sampling and detection difficult. Moreover, MPs have different characteristics compared to fluvial sediment (density, shape, mobility at the riverbed, etc): for these reasons the transport processes of these particles in rivers are not known and need to be deeply investigated. Most studies agree on the importance of WWTPs in estimating the balance of synthetic fibers deriving from the domestic washing processes, however, little is known about the mobility of these particles within WWTPs and also in rivers where little is known about the retaining capacity of sediments and aquatic vegetation.

The final target of this research regards the development and implementation of a new methodology based on the concept of MPs emission-based mass flow model using the sedimentological balance approach. The model will be implemented considering the main basic physical properties (size, density, shape) affecting the mechanics of entrapment, transport, and deposit of plastic particles. Particularly, accumulation of MPs within riparian and aquatic vegetation will be investigated. Also, MPs mobility into riverbed sediments will be taken into account. Finally, MPs dispersion from the Arno River to the Tuscan Archipelago will be investigated to better identify MPs hot spots along the Tuscan coastal waters.

The first phase of the research will be oriented to literature review to acquire a complete overview regarding the current state of the art about the MPs modeling methods in freshwater systems. The second phase will be focused on new data acquisition related to the loads of MPs influent and effluent from the WWTP of the metropolitan area of Florence to better understand the influence of anthropogenic factors on the MPs load and composition arriving in the aquatic environment. The third phase will regard the development of the mass balance model and laboratory invetigations about the role of aquatic vegetation in retaining MPs and about the interaction with the morphometry of the bed to calibrate and validate the model itself.

Laboratory experiments were started, both at the Laboratory of Hydraulics of the University of Florence about the study of the mobility of microplastics into the hyporheic zone, both at the Laboratory of Environmental Physics of the University of Girona about the role played by vegetation in lagoon areas in retaining microplastics and about how sediment concentration affect microplastics settling velocity. Numerous field sampling campaigns were also carried out (river Arno), to investigate the presence of microplastics both in water and in river sediments. Finally, the development of a GIS-based mass balance model is on-going, for the prediction of the amount of plastic (macro- and microplastic) inside the Arno basin.