Microplastic and microfiber contamination in the Tiber River, Italy: Insights into their presence and chemical differentiation.

Microplastics (MPs) are an emerging environmental concern, but studies on these contaminants, particularly in river ecosystems, remain scarce. Research has indicated that MPs in the environment are predominantly microfibers (MFs); however, a few studies suggest that the MFs encountered are chiefly of natural origin. In this study, we aimed to improve the understanding of MP/MFs (both plastic and natural), among microparticle (solid particles >10 μm to <5000 μm; mainly of plastic as well as natural origin) loads in the Tiber River, Italy, by analyzing the physicochemical properties of surface water and assessing the abundance and characteristics of MPs-MFs at three sites: Ponte Grillo, Aniene, and Magliana, along a 60 km stretch. MPs-MFs were visually inspected with a stereomicroscope and a fluorescence microscope and chemically characterized by FTIR. Interestingly, MP-MF concentrations were highest upstream at Ponte Grillo and lowest downstream at Magliana, an unconventional pattern likely related to atmospheric deposition and total suspended solids. Across sites, microparticles were mainly MFs, with MP fragments forming a minor fraction; at Ponte Grillo, Aniene, and Magliana, the MF abundances were 375.1, 58.1, and 28.8 items/L, respectively, while fragment abundances were 32.7, 14.4, and 4.8 items/L, respectively. At all sites, natural MFs (cellulose-based) were more prevalent than plastic ones (petroleum-based). The highest proportion of petroleum-based MFs, primarily PET, was observed at Magliana. Our findings indicate that although MPs-MFs in rivers stem from textile wear, laundry effluent, and WWTPs, atmospheric deposition is a dominant pathway, especially in remote, upstream, sparsely populated regions.