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Understanding not only microplastic (MP) concentration but also size distribution, morphology, and polymer profiles is desirable for stormwater, which is an important pathway of entry for MP into the aquatic environment. A challenge is that subsampling is often required for analysis of environmental samples and the impact of subsampling on the stormwater MP concentration determined and the polymer types identified is poorly characterized. To address this, MP were extracted from urban and suburban stormwater, including from green infrastructure. Fourier Transform Infrared microscopy was performed to characterize MP. In addition, particle dimensions and morphology were recorded. Varying the number of 63–250 μm particles subsampled per sample demonstrated the coefficient of variation for concentration (standard deviation/mean) for most samples was <0.3 when 20 particles (0.8–15% of total particles) or <0.2 when 30 particles (1.2–24% of total particles) per sample were analyzed. MP concentrations in the 63–250 μm size class ranged from 15 to 303 MP/L, one to two orders of magnitude greater than observed in previously reported paired samples from the 250–500 or 500–2000 μm size classes. A total of 25 plastic polymer types were observed across samples, more than observed in the large size classes. Spectral signatures of surface oxidation indicative of weathering were observed on most polyethylene, polypropylene, and polystyrene particles, which were the most abundant polymer types. Fragments were the dominant morphology with an average maximum length of 158 ± 92 μm. Overall, these results may help inform subsampling methods and be useful in future exposure assessments for aquatic organisms or design of MP removal technologies for urban and suburban stormwater.
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Stormwater runoff microplastics: Polymer types, particle size, and factors controlling loading rates
Stormwater runoff is a pathway of entry for microplastics (MPs, plastics <5 mm) into aquatic ecosystems. The objectives of this study were to determine MP size, morphology, chemical composition, and loading across urban storm events. Particles were extracted from stormwater samples collected at outfall locations using wet peroxide oxidation and cellulose digestion followed by analysis via attenuated total reflectance (ATR) FTIR. Concentrations observed were 0.99 ± 1.10 MP/L for 500–1000 μm and 0.41 ± 0.30 MP/L for the 1000–5000 μm size ranges. Seventeen different polymer types were observed. MP particle sizes measured using a FTIR-microscope camera indicated non-target size particles based on sieve-size classification, highlighting a potential source of error in studies reporting concentration by size class. A maximum MP load of 38.3 MP/m2 of upstream catchment was calculated. MP loadings had moderate correlations with both rainfall accumulation and intensity (Kendall τ = 0.54 and 0.42, respectively, both p ≤ 0.005). First flush (i.e. rapid wash-off of pollutants from watershed surfaces during rainfall early stages) was not always observed, and antecedent dry days were not correlated with MP abundance, likely due to the short dry periods between sampling events. Overall, the results presented provide data for risk assessment and mitigation strategies.
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- Award ID(s):
- 1917676
- PAR ID:
- 10511723
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Science of The Total Environment
- Volume:
- 929
- Issue:
- C
- ISSN:
- 0048-9697
- Page Range / eLocation ID:
- 172485
- Subject(s) / Keyword(s):
- Microplastics Cellulose digestion Stormwater runoff Rainfall Polymers FTIR
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.scitotenv.2024.172485
