An official website of the United States government
The Mississippi River System is of great ecological and economic importance, making it crucial to monitor contaminants within it. While nutrient pollution is well studied, there are little data on microplastics (MPs) in the Mississippi River System (MSRS), especially during drought conditions. Herein, we characterize MP pollution from seven sites across the MSRS during both flash drought and non-drought periods using FTIR microspectroscopy (µ-FTIR). Additionally, we evaluate the impact of multiple water level conditions on MP polymer composition across five time points at a single sampling site. Of all MPs identified, polyethylene terephthalate (PET, 22%), resin (17%), and polyethylene (PE, 10%) were the most abundant polymers. Average concentrations ranged from 16 to 381 MPs/L across seven sites, with no significant difference in concentration between conditions. Irregular particles were the most common morphology, with most MPs falling in the lowest size range measured (30–100 μm). Drought condition had a significant (p < 0.001) impact on polymer composition, and polymers most strongly correlated with flash drought were mostly fluoropolymers. For the single sampling site, concentrations differed, but not significantly, across the five timepoints. These results demonstrate the complex relationship between MP concentration and drought condition, and also highlight the importance of fully characterizing MPs in environmental studies.
more »
« less
This content will become publicly available on June 1, 2026
Polymer weathering under simulated solar radiation and comparison to stormwater and estuarine microplastics
Accurate spectral identification of weathered plastics and analyses that provide insight into environmental degradation and age are desirable for source tracking and understanding hazards. The objectives of this study were to (1) evaluate the kinetics of spectral changes for lab-weathered polymers and compare to spectra from environmental microplastics (MPs), and (2) assess the accuracy of spectral databases in identifying weathered polymers. For objective 1, polyethylene (PE) and polypropylene (PP) fragments were exposed to simulated solar radiation in water for 90 days. FTIR spectra were collected periodically and degradation was quantified using carbonyl and hydroxyl bond indices. Significant linear increases in carbonyl indices for PP, but not PE, were observed as a function of exposure time. Spectra (via principal component analysis) and bond indices from lab-weathered polymers were then compared to environmental MPs collected from urban stormwater and the Delaware Bay estuary. Estuarine PP carbonyl and hydroxyl indices varied as a function of spectral collection mode (i.e., ATR vs. transmission) and by sampling site, potentially indicating the bond indices provide insight into sources/fate/transport of PP and are worthy of further study. In contrast, no significant differences were observed for PP in stormwater samples, possibly due to the close proximity of collection locations. PE exhibited non-linear trends in bond indices in the laboratory study and showed no significant association with sampling location in environmental samples, suggesting these indices may be less useful for PE degradation analysis. For objective 2, 14 different polymers, eight of which were polymer blends, were exposed to simulated solar radiation for up to 90 days, in dry and wet conditions. FTIR spectra were collected periodically and analyzed with two spectral identification software. OpenSpecy achieved an 88 % true positive rate compared to siMPle's 57 % at a 70 % hit quality threshold. Expanding reference libraries, to include weathered polymers and polymer blends, could improve spectral identification accuracy, and manual interpretation of FTIR spectra is recommended for low-confidence matches.
more »
« less
- Award ID(s):
- 1917676
- PAR ID:
- 10633889
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Chemosphere
- Volume:
- 379
- Issue:
- C
- ISSN:
- 0045-6535
- Page Range / eLocation ID:
- 144379
- Subject(s) / Keyword(s):
- Polymer weathering Simulated sunlight Polyethylene Polypropylene Spectral identification FTIR Microplastic
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Fourier transform infrared (FTIR) and Raman microspectroscopy are methods applied in microplastics research to determine the chemical identity of microplastics. These techniques enable quantification of microplastic particles across various matrices. Previous work has highlighted the benefits and limitations of each method and found these to be complimentary. Within this work, metadata collected within an interlaboratory method validation study was used to determine which variables most influenced successful chemical identification of un-weathered microplastics in simulated drinking water samples using FTIR and Raman microspectroscopy. No variables tested had a strong correlation with the accuracy of chemical identification (r = ≤0.63). The variables most correlated with accuracy differed between the two methods, and include both physical characteristics of particles (color, morphology, size, polymer type), and instrumental parameters (spectral collection mode, spectral range). Based on these results, we provide technical recommendations to improve capabilities of both methods for measuring microplastics in drinking water and highlight priorities for further research. For FTIR microspectroscopy, recommendations include considering the type of particle in question to inform sample presentation and spectral collection mode for sample analysis. Instrumental parameters should be adjusted for certain particle types when using Raman microspectroscopy. For both instruments, the study highlighted the need for harmonization of spectral reference libraries among research groups, including the use of libraries containing reference materials of both weathered plastic and natural materials that are commonly found in environmental samples.more » « less
-
Stormwater runoff microplastics: Polymer types, particle size, and factors controlling loading ratesStormwater 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.more » « less
-
Microplastics pose a significant environmental threat, and understanding their sources and generation mechanisms is crucial for mitigation efforts. This study investigates the effects of ultraviolet intensity, temperature, and relative humidity on the degradation of polyethylene terephthalate (PET) plastics and the subsequent formation of microplastic particles. PET samples were exposed to ultraviolet (UV) radiation under various environmental conditions using the SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) accelerated weathering device at the National Institute of Standards and Technology (NIST). Attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and laser confocal scanning microscopy (LSCM)/atomic force microscopy (AFM) were employed to characterize the chemical and morphological changes on the weathered surfaces. This study’s findings reveal that temperature and relative humidity significantly influence the rate of photodegradation and the characteristics of the generated microplastics. Higher temperatures and increased humidity accelerated the degradation process, leading to a higher abundance of microplastic particles. However, larger particles were observed at higher temperatures due to aggregation. These results underscore the importance of considering environmental factors when assessing the fate and transport of microplastics in the environment. Developing strategies to reduce plastic pollution and mitigate the generation of microplastics is essential for protecting ecosystems and human health.more » « less
-
Abstract Identifying and removing microplastics (MPs) from the environment is a global challenge. This study explores how the colloidal fraction of MPs assemble into distinct 2D patterns at aqueous interfaces of liquid crystal (LC) films with the goal of developing surface‐sensitive methods for identifying MPs. Polyethylene (PE) and polystyrene (PS) microparticles are measured to exhibit distinct aggregation patterns, with addition of anionic surfactant amplifying differences in PS/PE aggregation patterns: PS changes from a linear chain‐like morphology to a singly dispersed state with increasing surfactant concentration whereas PE forms dense clusters at all surfactant concentrations. Statistical analysis of assembly patterns using deep learning image recognition models yields accurate classification, with feature importance analysis confirming that dense, multibranched assemblies are unique features of PE relative to PS. Microscopic characterization of LC ordering at the microparticle surfaces leads to predict LC‐mediated interactions (due to elastic strain) with a dipolar symmetry, a prediction consistent with the interfacial organization of PS but not PE. Further analysis leads to conclude that PE microparticles, due to their polycrystalline nature, possess rough surfaces that lead to weak LC elastic interactions and enhanced capillary forces. Overall, the results highlight the potential utility of LC interfaces for rapid identification of colloidal MPs based on their surface properties.more » « less
