Detection of Atmospheric Microplastics Accumulated in Xanthoria parietina: A Lichen Biomonitoring Study on the Asian Side of Istanbul

Airborne microplastics have become invisible global threats to all living organisms today. This study was designed for the first time to monitor atmospheric microplastic pollution in the city of Istanbul (Turkiye) through lichens, known as air pollution biomonitors. Epiphytic foliose lichen Xanthoria parietina was sampled from forested areas in 8 different districts on the Asian side of megacity, and searched for clues of microplastics through chemical characterization and microscopic examination. Twelve compounds (aldehyde, alkene, amine, carboxylic acid, ether, hydrocarbon, hydroxide, ketone, methyl, methylene, nitrogen dioxide, and sulfur dioxide) were identified as microplastic components in urban lichen samples taken from all localities with the FT-IR technique used in polymer identification. The most accumulated compound in lichen samples was amine, which is formed as a result of the chemical degradation of plastics. Building blocks of microplastic particles (MPs) such as aldehydes, carboxylic acid and methylene, as well as air pollutants such as SO₂ and NO₂ were also detected. Analysis data were supported by microscopic observations made by applying fluorescent staining method to lichen thalli and MPs were also detected visually. The highest number of MPs seen in the lichen thalli was detected in samples taken from touristic areas in Üsküdar district. Based on the results, in addition to human impact, intense atmospheric microplastic compounds identified by lichen monitoring on the Asian side of Istanbul suggest that these pollutants may have been transported from local plastic waste or industrial areas. This study shows that biomonitoring studies of airborne organic pollutants such as microplastics can be done through lichens.

Graphical Abstract