Microplastics in Atmospheric Pathways, Depositions, and Remediation Techniques

Airborne microplastics (MPs) in different morphological forms (e.g., fibers, fragments, and films) with their size commonly between 1 μm and 5 mm has become an emerging concern globally due to their widespread presence in various environmental compartments, such as the hydrosphere, lithosphere, and atmosphere. MPs are complex and dynamic mixtures of polymers, minerals, byproducts of plastic degradation, and other chemicals that may undergo photochemical reactions under sunlight and releases various ubiquitous contaminants of great concern for the environment and human health. Microplastics exposure to human health causes DNA damage, oxidative stress, and inflammation that can be chronic sometimes. There are broadly two types of MPs: primary MPs, purposely produced for commercial use, and secondary MPs, which are fragmented pieces from larger plastic as a result of their use, aging, and decaying through weathering. Atmospheric transport mechanisms that include wind dispersion and atmospheric turbulence predominately enable microplastics to travel long distances, potentially crossing regional and even continental boundaries. This study provides the overview of the current status of the ambient presence and understanding about microplastics that humans are most likely exposed to, their sources, transportation pathways, their deposition mechanisms in the environment, and their prospective mitigation technologies. The primary source MPs include vehicle tire wire, personal care products, paint, sewage sludge, plastic pellets, etc., whereas secondary MPs, which are created by the fragmentation or degradation of primary MPs, include agricultural wastes, municipal refuse like used plastic water bottles, marine debris like fishing wastes, and others. Once airborne, MPs can undergo various processes that influence their deposition, including dry and wet deposition. Dry deposition occurs when particles settle directly onto surfaces due to gravity, while wet deposition involves microplastics being scavenged by precipitation events, such as rain or snow. These deposition processes lead to the accumulation of MPs in diverse environments, including terrestrial ecosystems, freshwater bodies, and even remote polar regions. Various physical, chemical, and biological strategies have been attempted for remediation of MPs pollution. One of the most effective mitigation techniques is bioremediation, which uses biological organisms to degrade MPs. It is basically a four-step process: biodegradation, biofragmentation, assimilation, and mineralization. In most cases, microbes are used in the bioremediation technique, and sometimes plants, earthworms, microalgae are also used. Chemical remediation techniques include agglomeration, which forms larger particles for removing the MPs and an advanced oxidation process where plastic degraded material is oxidized in the presence of a catalytic reagent. Membrane technology is a remediation technique that involves the physical removal method. Additionally, research for innovative materials and coatings that can capture or degrade MPs is ongoing, which will offer potential solutions for reducing their atmospheric presence. This study will be a basis for identifying the type of source and transport-deposition mechanism needed to develop suitable remediation schemes in different conditions for an MPs-free sustainable environment.