Microparticles investigation in fluvial and lagoon systems: environmental impact and development of sampling and analytical protocols.

Anthropogenic microparticles (MPC), like microplastics (MPs), are widespread in natural environments and they are considered a leading threat to ecosystems, also for the possibility to act as vectors for other contaminants like heavy metals. Despite the growing attention of the scientific community for these microparticle pollutants, several key systems in the terrestrial compartments remain largely understudied. Among them, fluvial systems, which are among the main contributors of MPC to the sea, are almost unstudied, especially in Italy. The overall aims of this PhD thesis were to (i) assess and characterise MPC contamination (i.e., MPs and natural-based textile fibers, MF TEX ) in water and sediment matrices of fluvial and transitional systems of the Arno River and Orbetello Lagoon (Central Italy), (ii) estimate MPC contribution from the Arno River to the Mediterranean Sea, (iii) set up specific and semi-automated methods for sampling, extraction and analysis of MPC in fluvial and lagoon systems, coupling the two-fold aims of analysing the smallest MPC as possible, which are mostly overlooked in literature, with the sampling of great volume of water to increase representativeness, and (iv) highlight MPs-mercury interactions under simulated riverine waters enriched in Hg. Results from the Arno River investigation suggest MPC contamination in shallow waters and riverbank sediments all along the fluvial pathway. In particular, outcomes from waters suggest an extreme contamination (up to 6×10 4 particles/L) of microparticles 5 to 5000 µm in size (hereafter MPC TOT ) strongly driven by microparticles 5 to 59 µm in size (hereafter MPC <60 ), which account for >99% of total particles found and whose abundance increases inversely with particle size. Microparticles 60 to 5000 µm in size (hereafter MPC ≥60 ), which account for <0.5% of MPC TOT , highlighted a predominance (76% of the total) of natural- based textile fibers (MF TEX ) and synthetic polymers microfibers (e.g., PET), suggesting strong contributions from domestic and industrial laundry effluents. Specifically, MF TEX represent around 70% of all MPC ≥60 . At the outlet, fluxes indicated that the Arno River discharges approximately 4.6×10 15 MPC TOT annually to the Mediterranean Sea. Fluxes are highly dependent on seasonality, with a MPC TOT delivery of 2.4×10 13 particles/day and 1.2×10 12 particles/day during wet and dry seasons, respectively. The total mass of discharged MPC TOT is estimated at about 30 tons/year (t/y); the MPC ≥60 fraction amounts to about 8 t/y, and MF TEX to about 1 t/y. In the riverbank sediments of the Arno River, MPC abundances range from 20±6 to 2,960±941 particles/kg d.w. Significant concentrations (up to 380 particles/kg d.w.) of MF TEX were highlighted, accounting for 21% of the total number of MPC found along the river. A relevant amount of plastic microlitters (25% of the total) can be associated with tire and road wear particles (TRWPs), suggesting a strong contribution from vehicular traffic mainly characterising the urbanised areas of the fluvial basin, and peri-urban landscapes crossed by principal national routes. For both the river phases investigated, the metropolitan area of Florence is identified as MPC hotspot, being impacted by the most intense urbanisation and over-tourism activities of the catchment. Furthermore, MPC such as MPs show a greater repartition in river sediments than waters, highlighting the role of the Arno riverbanks as a sink for MPC. However, this sink is only temporary, because spring rainfalls occur in the catchment and promote MPs re- suspension mechanisms. In the Orbetello Lagoon waters the occurrence of MPC (9.8 to 40.0 particles/m 3 ) is associated with fishing activities and textile laundering effluents from the surrounding anthropized areas. Considered a nationally relevant site for aquaculture, this transitional system could suffer potential impact on ecosystems and fish farms. The specific methodology developed for the MPC investigation in waters of fluvial systems consists of innovative and plastic-free equipment for the collection of representative and small-volume samples. For the investigation of lagoon systems, a semi-automatic trawl technique was set up for reliable and efficient MPC sampling in shallow waters. These methods allowed to effectively determine small-size MPC in the Arno River and the Orbetello Lagoon waters, which represent by far the most abundant fraction of MPC. In addition, the developed methods point out the critical problem concerning the lack of standardized methods for MPC sampling, processing, and analysis. Greater uniformity of methods is required to facilitate comparisons among studies and clearly understand the environmental and ecological impact of microlitter particles. Laboratory experiments simulating MPs-mercury interaction in natural riverine waters enriched in Hg, demonstrate the ability of polypropylene (PP), one of the most abundant MPs polymers in natural systems, to adsorb Hg. This highlights the potential role of MPs as carriers of Hg under riverine conditions. This research calls for further investigations on the ecotoxicological hazard associated with the desorption of Hg from MPs in gastrointestinal fluids of riverine fish species. Data and results presented in this thesis provide useful information on microparticles contamination in poorly documented water systems. Furthermore, this thesis encourages new studies to be more comparable and highlights the challenges of aiming for environmental and ecological relevance.