Assessing the deposition of airborne microplastics using vegetation

The increasing global concern over the prevalence of microplastics (MPs, plastic particles <5 mm) in the environment, coupled with their recent identification in the atmosphere, underscores the potential for direct human exposure. Traditional studies on airborne MP deposition often rely on specialized infrastructure and labor-intensive sampling networks, limiting spatial observations. This PhD thesis addresses this challenge by focusing on the novel use of passive biomonitors —an accessible and cost-effective tool for monitoring atmospheric pollution— to assess airborne MP deposition. The different chapters of this thesis highlight the evolution of the research, emphasizing key issues. Chapter 1 compares the suitability of the epiphytic lichen Evernia prunastri to the epigeic moss Pseudoscleropodium purum as biomonitors in central Italy, and suggests that epigeic moss is preferable for passive biomonitoring due to its structural characteristics and habitat position. Chapter 2 investigates the deposition of airborne MPs in Tuscany, central Italy, using pleurocarpous moss at 33 remote sites, revealing the effectiveness of passive biomonitoring for high spatial resolution assessments of regional-scale MP deposition. In Chapter 3, the study expands to the European scale, assessing MPs using moss biomonitoring across 37 remote sites from 17 countries, indicating the feasibility of mosses for large-scale assessments of atmospheric MP deposition, and highlighting the influence of population density on atmospheric MP abundance (count and mass). Chapter 4 focuses on understanding the contribution of tire wear particles (TWPs) using Robinia pseudoacacia L. (black locust) leaflets in Siena, Italy, which was motivated by the discovery of TWPs in moss samples collected throughout the region of Tuscany, coupled with the abundant presence of this invasive tree species along roads. The results showed the suitability of Robinia as a biomonitor for airborne MPs, including TWPs. Overall, this thesis establishes the effectiveness of biomonitors in assessing airborne MP deposition, providing valuable insights for environmental research and air quality management.