Emerging environmental challenge: a critical review of airborne microplastics

Trillions of micro- and nanoplastics are ubiquitously dispersed in the environment owing to relentless human reliance on plastics implying constant human exposure to these tiny synthetic particles. Unlike terrestrial and aquatic microplastics, research on airborne microplastics (MPs) is very limited and needs to be expanded to explore their prevalence, fate, and health risks fully. This study effectively assesses available studies conducted on microplastics' presence in atmospheric deposition, and indoor and outdoor air samples, and highlights disparities in employed methodological approaches. Six different databases have been consulted to procure data (2015-24) for this review study. The number of studies directly investigating MPs in the air is very low which limits knowledge concerning the sources, fate, and attributable human health risks. MPs abundance indoors ranges from 0.13 to 14088.05 items/m(3), while in outdoors it ranges from none to 393 items/m(3). Indoors are significantly more contaminated than outdoors, raising considerable health concerns given that people spend most of their time indoors. Airborne microplastics are predominately fibrous (88%) indicating textiles as a major source. Polyethylene, polypropylene, polyethylene terephthalate, and polystyrene are the most prevalent polymers implying their excessive use in the environment. Inhalable microplastics (particularly <5 mu m) have been very scarcely investigated. Further research is imperative to investigate airborne MP toxicity, global dispersion patterns, interactions with other pollutants, and potential health impacts on humans, animals, and plants. In the final section of this study, numerous recommendations for future research are made to address the research gaps revealed in the existing literature.