Identifying Spatial and Environmental Correlates of Airborne Microplastics and Nanoplastics across Philadelphia

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Summary Due to the massive production and careless disposal of plastic waste, plastic pollution and its potential health effects have drawn attention recently. The annual production of plastic materials was approximately 370 million tons in 2019 and is expected to increase continually. During the Coronavirus Disease 2019 (COVID-19) pandemic, the production of plastics in the world skyrocketed to 584 million tons in 2020 due to an unprecedented demand for single-use plastics. More than half of the plastic waste generated worldwide is thrown away into the environment without proper management. Of the various sizes of plastics, much attention has focused on the smaller sized plastics such as microplastics (1 µm to 5 mm) and nanoplastics (< 1 µm). Microplastics and nanoplastics (MANs) contain thousands of harmful chemicals (i.e., plasticizers, flame retardants, and other toxic organic chemicals), and MANs are easily absorbed into humans and other living organisms, potentially causing respiratory inflammation, systemic oxidative stress, and neurotoxic effects. Hence, their ubiquity in environments and the ease with which they can be absorbed has raised concerns about the potential impact of exposure to MANs on human health. Although ingestion of MANs was considered to be the primary route of exposure, recent reviews suggest that inhalation of MANs may be two to three orders of magnitude greater than ingestion of MANs. While the information on human exposure to inhalable MANs is a fundamental step in determining human health risk, there are several knowledge gaps for exposure assessment of airborne MANs. Exposure assessment of outdoor air MANs in the United States (U.S.) has not yet been conducted, yet people living in densely populated urban areas are likely at risk for significant exposure to airborne MANs. As the second poorest major city in the U.S. (23% poverty rate), many Philadelphians (especially people of color) without air conditioning units spend more time outside or with the windows open in warmer months, thereby increasing their exposure to outdoor air MANs. To date, the spatial variation of ambient air MANs in urban areas has not been assessed. Additionally, the specific composition of MANs, the distribution of these components, and their likely sources in urban environments are unknown. This study will address these gaps. Specifically, we aim to (1) collect ambient air MANs at 48 different sampling sites, quantify inhalable size of MANs and characterize their composition, (2) characterize the geographic distribution of airborne exposure to MANs (and their chemical composition) across Philadelphia, Pennsylvania, and (3) identify environmental correlates of higher MANs levels and explore seasonal differences. This proposed exploratory study is directly responsive to NIEHS strategic goals “Emerging Environmental Health Issues.” Airborne MANs are emerging pollutants and their related health effects are largely unknown locally and globally. Quantifying exposure to airborne MANs will provide necessary data for future health studies to determine the potential risks of airborne MANs to human health.