Microplastics distribution in marine sediments offshore the Tiber River mouth (Central Tyrrhenian Sea): the role of sedimentary processes

Plastic litter is nowadays ubiquitous in all environmental compartments of the world's oceans and rivers are globally recognized as main entry points for plastic at sea. However, our knowledge of the processes driving land-to-sea transfer and dispersal patterns of plastics is still limited. In this work, we investigated the distribution of microplastics (MPs) in fluvial and marine sediments both along the lower reach of Tiber River, up- and downstream the city of Rome, and in the marine sectors off the river mouth from 10 to 100 m depth. Sampling strategy in the marine areas was aimed at assessing MPs distribution and composition in different morphological zones of the submarine delta, from the inner delta front to the lower prodelta slope. This allows us to evaluate the role of sedimentary processes on the transport and deposition of MPs. To assess potential relationships with sediment texture, grain size analysis on sediment samples was also carried out. Results show a large variability in the abundance and polymeric composition of MPs across the study area, with concentrations ranging from 100 to over 2000 items/kg. The maximum abundances are found on the upper prodelta slope, at 40-50 m depth, an area with high sedimentation rates and silty sediments. Much lower concentrations are observed in the shallower stations characterized by sandy sediments, suggesting MPs bypass over the inner delta front likely facilitated by wave-induced resuspension. Furthermore, the stations north to the river mouth show higher abundances compared to those located in the southern prodelta, possibly indicating a lateral deviation of MPs transported by the river plume in response to the main northward-flowing Tyrrhenian currents. Findings from this study suggest that deltaic environments may act as a sink for MPs, also highlighting the importance of taking into account sedimentary dynamics to deepen our knowledge regarding MPs distribution. Also see: https://micro2024.sciencesconf.org/559160/document