Lichen Biomonitoring of Airborne Microplastics in Milan (N Italy)

Simple Summary The atmospheric deposition of microplastics (MPs) is a growing concern for human health. In this research, we studied the deposition of airborne MPs in urban areas of Milan and a remote area in North Italy using lichen transplants. The results demonstrate that lichens are suitable biomonitors for studying airborne MPs. The findings of airborne MPs, even in remote areas, indicate the inevitable exposure of humans and, therefore, potential health risks. This study investigated the deposition of airborne microplastics (MPs) in the urban area of Milan across 12 sites and at a background control site (northern Italy) using 3-month transplants of the fruticose lichen species Evernia prunastri (exposed in triplicate). The primary objective was to evaluate the use of lichen transplants for the assessment of MP deposition; as such, the study sites spanned a gradient in vehicular traffic and population density across four concentric land-use zones (i.e., urban parks, centre, semi-periphery, and periphery). A total of 149 MP particles were detected in the exposed lichen samples; 94.6% were classified as fibres and 5.4% as fragments. The control site and urban parks experienced a similar number of MPs per gram of dry lichen (20-26 MP/g), while a higher number of MPs were detected in central and peripheral areas (44-56 MP/g), with a clear increasing gradient from the city centre towards the periphery. We estimated the MP deposition in Milan to be in the range of 43-119 MPs m(2)/d, indicating that people living in Milan are exposed to airborne MPs, with potential health effects. This study suggests that lichens are suitable biomonitors of airborne MPs under a relatively short exposure of three months in urban environments.