Microplastics Aloft: A comprehensive exploration of sources, transport, variations, interactions and their implications on human health in the atmospheric realm

Microplastics (MPs), particles with a size <5 mm, are ubiquitous in water, soil, and atmosphere, and have become a highly discussed environmental issue. Although atmospheric MPs have received less attention than MPs in soil and water, their possible environmental consequences are being examined in more depth. This study systematically reviews the sources, transport, distribution, and variations of atmospheric MPs, their interactions with other pollutants in the environment and impact on human health based on the literature. The results show that MPs have been identified in diverse atmospheric settings such as urban, sub-urban, and remote areas as well as in indoor air. These airborne MPs can originate from terrestrial sources like landfills, synthetic clothing, and plastic manufacturing, use and recycling activities, as well as from aquatic sources like MPs resulting from bubble bursting. The outdoor MP abundance was detected in a range of 2 to 1159 MP/m²/day in depositions and 0 to 224 MP/m³ in suspended samples, while significantly higher abundance was observed indoors with depositions ranging from 22 to 760,000 MP/m²/day and suspended from 0.4 to 1583 MP/m³. The distribution characteristics of atmospheric MPs are affected by several factors such as urbanization, anthropogenic activities, indoor and outdoor environments and seasons. Atmospheric transport of MPs occurs through suspension, horizontal transport and deposition processes that are greatly influenced by the morphology of the MP, wind speed and direction, precipitation and other atmospheric factors. The transport path of MPs in the atmosphere is studied by Lagrangian atmospheric models by conducting backward trajectory simulations to estimate linear trajectories of MPs at sampling locations to discern their potential origin and travel distance. MPs can also interact with a variety of chemical pollutants and microorganisms in the environment and thus act as a vector for pollutant transport. The toxicity of MPs may be increased by the release of pathogens and chemical contaminants into the environment, thereby increasing the health risk to humans. Based on the study, it is suggested that further scientific research on atmospheric MPs should focus on the standardization of research methods, atmospheric transport mechanisms, interactions of MPs with atmospheric pollutants and ecological impacts. As MPs could enter the human body through various mechanisms, it is urgent to study their physiological effects on the human body when exposed to atmospheric MP pollution.