A systematic review of airborne microplastics emissions as emerging contaminants in outdoor and indoor air environments

Microplastics (MPs), the emerging contaminants of the present century, are potentially a major threat to human health and ecology. There is currently no comparison of the properties of MPs in indoor and outdoor air. Thus, there is a need a systematic review (SR). The goals of this study were to answer the following questions: (1) what are the geographical distribution, sources, abundances, and characteristics (polymer, type, shape, color, size) of MPs in outdoor and indoor air? (2) What are the limitations of the published studies and recommendations for future research? To achieve these objectives, four electronic databases were searched to find works published before December 31, 2022. In total, 37 publications were selected based on the PRISMA guidelines. The study found that polyester and polyethylene terephthalate were the most dominant polymer types in outdoor and indoor environments, respectively. The most important indoor sources for MPs included synthetic textiles, kitchen plastic utensils, synthetic fiber carpets, detergents, and furniture, while the most important sources for outdoor MPs include industrial emissions, particulate emissions from vehicles, burning of plastic waste, the expulsion of air bubbles and wave action in ocean and decomposition and destruction of plastic materials. Fibers were the dominant shape of airborne MPs in both environments. The predominant colors of the MPs in samples of the indoor air were white and transparent, whereas black was most abundant in the microplastic samples collected from the air outside the building. Finally, given the ubiquitous nature of MPs and their potential for adverse effects, governments should take effective measures to reduce the production of plastic materials and finally increase plastics reuse, and recycling rate.