Dry and Wet Deposition of Atmospheric Microplastics in Las Vegas, Nevada

Plastics have been one of the most widely used man-made materials since their inception, and production is expected to grow by five percent every year. Plastic waste has become a growing global environmental issue. Primary MPs are plastics that are created to be intentionally tiny for their specific functional purpose. Secondary microplastics (MPs) are byproducts of plastic waste occurring due to the breakdown of larger plastics resulting in the presence and accumulation of MPs in the environment. MPs are defined as tiny particles of plastic between 5 mm and 1 μm in size. MPs have been found in the deep ocean, freshwater systems, soil, the atmosphere, and even the human body. Some of Earth’s most remote regions with virtually no humans have been contaminated with MPs suggesting that the atmosphere is a major channel in MPs transport and deposition. The impact atmospheric deposition of MPs has on environmental MPs pollution is unclear due to a lack of research. Being able to identify the potential sources of MPs in the environment is a necessary step in MPs pollution control.This study presents the first evidence of dry and wet deposition of atmospheric MPs in the City of Las Vegas, Nevada. Atmospheric dry and wet deposition samples were collected for a year and MPs deposition fluxes in wet versus dry weather were quantified and compared. The MPs dry deposition fluxes ranged from 3.84×103 to 8.12×104 MPs/m2/day and wet deposition fluxes ranged from 1.53×104 to 1.43×106 MPs/m2/day. The majority of deposited MPs from both wet and dry weather were < 25 μm particles. On average, MPs deposition fluxes in dry weather during spring and winter months were higher than those in fall and summer months. Precipitation events promoted the deposition of atmospheric MPs. Overall, MPs deposition flux per day in wet weather was greater than that in dry weather. MPs dry and wet deposition fluxes were compared to particulate matter (PM) concentrations. MPs wet deposition flux showed a moderate (with outlier) to fairly strong (without outlier) correlation (R2 = 0.560 – 0.778) with average PM10 concentrations prior to rainfall, and a moderate correlation (R2 = 0.577) without the outlier with average PM2.5 concentrations prior to rainfall. The relationships between MPs wet deposition flux and PM2.5 concentrations prior to rainfall with the outlier and the removal effect of precipitation on PM10 and PM2.5 were not statistically significant. MPs dry deposition fluxes and PM10 and PM2.5 concentrations had weak to no correlation and were not statistically significant. These results highlight the importance of atmospheric MPs deposition as a source of environmental MPs pollution.