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Abundance and characteristics of microplastics in stormwater runoff from parking lots and roadways on a university campus
Summary
Rain events washing over university parking lots and roads release pulses of microplastics into stormwater drains, with concentrations spiking at the start of rainfall and rapidly declining—a pattern called the 'first flush' effect. Samples from the University of Mississippi showed concentrations as high as 128 particles per liter at the onset of rain, dropping to around 6–8 particles per liter after 30 minutes. Most particles were small fragments (30–150 µm) of nylon, polyethylene, and polypropylene—plastics consistent with tire wear, synthetic textiles, and road-associated debris. This highlights urban stormwater as a direct conduit carrying microplastics from roads to receiving waterways with every rainfall event.
The release and profile of microplastics (MPs) in surface runoff from parking lots and roadways is poorly understood. Here, we quantified and characterized MPs in runoff samples ( n = 21) from the drainage outlets of two such areas at the University of Mississippi during two separate rain events. Samples were analyzed using a combination of optical microscopy and Fourier Transform Infrared micro-spectroscopy (µ-FTIR). MP concentrations (particles/L ± 1SE) at the onset of the storm event and after 30 minutes varied from 128 ± 114 to 8 ± 4 for the first event, and from 17.3 ± 3 to 6 ± 2.5 for the second event, respectively. Both rain events demonstrated the first flush phenomenon, where pollutants are readily washed from the surface in the early stages of runoff. Most of the particles (91%) ranged between 30-150 µm in size, with 30 µm being the lowest size measured. Irregular particles (fragments) were dominant (50%), followed by spherical particles (32%) and fibers (18%). The top abundant types of MPs detected were acrylonitrile butadiene styrene (12%), polycarbonate (12%), polyurethane (11%), polymethyl methacrylate (10%), polyethylene terephthalate (8%), polyvinyl chloride (7%), ethylene vinyl acetate (6%), ethylene propylene (6%), polyamide (5%) and polyacrylamide (4%). Sources of MPs include plastic litter that has fragmented and road wear particles that can include reflective coatings. Even with limited spatial and temporal sampling, these findings indicate that parking lots and roadways at the investigated sites serve as significant sources of MP pollution in stormwater runoff. Consequently, analogous sites merit examination to better characterize the scope and mechanisms of this environmental input. • High concentrations of microplastics were detected in stormwater runoff during rain events on a university campus. • ABS, PC, PU and PMMA were the most dominant microplastic types identified in the runoff samples. • Over 90% of the microplastics observed ranged in size from 30 to 150 µm. • Parking lots and roadways on campus were identified as major contributors to microplastic pollution in stormwater runoff.
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