MICRO- AND NANOPLASTIC: FATE IN THE FRESHWATER ECOSYSTEM, FORMATION THROUGH THE USE OF PLASTIC WATER BOTTLES, AND A MODEL FOR HUMAN HEALTH RISK EVALUATION

Although the degradation of plastics is desirable, the degradation products of plastic materials, micro- and nanoplastics, are of increasing concern. These plastic particles are now emerging pollutants in the environment and are considered potentially hazardous to organisms and humans. This thesis had the scope of giving further insights into the understanding of these pollutants by addressing fate, generation, detection and effects on human health. In detail, the following questions were posed: How do microplastics distribute in a river ecosystem and does the biotic microplastic pollution reflect that of the abiotic matrices? Can the use of plastic packaging generate plastic particles? How are nanoplastic particles chemically modified during secondary formation, and through which analytical approach can they be identified and quantified? What are the human health effects of inhaled microplastics, and is the 3D structured human airway organoid model suitable for human risk assessment of atmospheric plastic particles? For investigating the occurrence and fate of microplastic in a freshwater ecosystem, two projects were conducted on the Ticino River (North Italy); one on microplastics extracted from multiple matrices (water, sediment, fish and macroinvertebrates) simultaneously sampled along the river and one on microplastic isolated from pellets of an avian freshwater species. The results demonstrated a high complexity of the distribution of microplastics along the river, evidenced by the absence of correlation of concentration between the matrices and along the river, and that a single matrix alone cannot accurately represent the microplastic pollution level of a river ecosystem. Moreover, the spatial variability and the opposing microplastic concentrations in water and sediment further indicates a strong role of the pronounced hydrodynamic conditions of the Ticino River, where microplastics can be deposited, retained and resuspended. Furthermore, using regurgitated pellets and a tied use of different analytical techniques, here µ-FTIR and SEM-EDS, were proven to be a suitable approach for identifying (micro)plastics for avian plastic ingestion studies. The formation of plastic particles from packaging was investigated in two further projects focusing on the release of micro- and nanoplastic particles from drinking water plastic bottles (single-use) under simulated use. The results demonstrate that the bottle lid (made of high-density polyethylene) was the source of the formation of plastic particles, which were also detected on bottlenecks and, therefore, available for human exposure via ingestion. In this context, the modifications of the physical-chemical characteristics of secondary nanoplastic particles were detected and described. High resolution SEM, XPS, SPES and µ-Raman analysis, in combination with concentration steps proved to be suitable for quantifying and identifying nanoplastics in simple matrices like drinking water. The last project was dedicated to an innovative model for the risk evaluation of inhaled and deposited atmospheric micro- and nanoparticles on humans. In this work, 3D human airway organoids were characterised and exposed to synthetic microplastic fibres released by drying textiles in a tumble dryer. The result shows that the presence of nonbiodegradable fibers during the repair phase of a damaged lung epithelium may lead to their inclusion in the repaired tissue with unknown effects on long term perspective. Concluding that human airway organoids are suitable for testing airborne micro-and nanoplastics to determine the potential risks of atmospheric particles in developing adverse pulmonary effects, this thesis contributes to the development of urgently needed human models for assessing the impact of particulate matter pollutants. Covering different aspects of micro- and nanoplastic pollution, this thesis contributed to understanding the complexity of this pollutant and to the optimisation of future micro- and nanoplastic research regarding the evaluation of environmental concentrations, human exposure of plastic particles from packaging and human risk evaluation of atmospheric particulate matter. Also, with a perspective on the future of plastic materials (here packaging and textiles), the results of this work should stimulate and be taken into consideration for the re-design of plastic materials.