Greenspaces can reduce the level of airborne microplastic contamination in urban environments: Evidence from a lichen...

Microplastics (MPs) have been found across a variety of environments, nonetheless few studies have evaluated atmospheric MPs. In this study, airborne MP contamination was investigated using transplants of the fruticose lichen Evernia prunastri in urban sites. Lichen transplants were exposed for seven weeks (April to June 2023) in parking lots (n = 9) and urban parks (n = 9) in the city of Pisa (Tuscany, Central Italy); in parallel, native samples from rural areas (n = 4) were also investigated. The overall aim was the characterization of MPs in terms of number, shape, size and polymer composition under different environmental conditions. Further, the positive role of green urban areas in buffering atmospheric MPs was assessed. We found MPs, including fragments, fibres and tyre wear particles, across all sites. The average number of MPs (per gram dry weight of lichen) significantly increased from rural areas (2 ± 0.4 MP/g dw) to urban parks (7 ± 1.1 MP/g dw) and parking lots (16 ± 4.1 MP/g dw). Average daily MP deposition rates across sites in urban areas was in the range of 12-143 MP/m²/d, suggesting that inhabitants are exposed to varying levels of airborne MPs. There was no difference in the length of the fibres between parking lots and urban parks; however, longer fragments and shorter tyre wear particles were found in parking lots. Polyethylene terephthalate was the dominant polymer detected across sites. The transplants maintained their overall vitality after the exposure (assessed by chlorophyll a fluorescence emission analysis), similar to native samples from rural areas, suggesting that the exposure had a negligible effect on lichen metabolism. Overall, our results suggest that lichen transplants are effective biomonitors of atmospheric MPs in urban areas, and that the presence of greenspaces (parks) in urban environments can significantly buffer the level of atmospheric MPs.