Micro-Infrared Spectroscopy Reveals Polymer-Specific Risk Profiles of Riverine Microplastics in Chengdu, China

Microplastics have emerged as a considerable global environmental issue collecting substantial notice from the public as well as from their governments. In a joint study conducted by researchers at Chengdu University of Technology, the Chengdu Environmental Monitoring Center Station of Sichuan Province, and Chengdu University, microplastics (0.02-5.0 mm) in the surface water of the Minjiang River and Tuojiang River valleys in Chengdu were quantitatively characterized and analyzed using micro-infrared (IR) spectroscopy. Key metrics such as the pollution load index, polymer risk, and potential ecological risk index were calculated to evaluate and analyze the risks associated with microplastics. A paper based on this work was published in Scientific Reports.¹

The mass production of plastics began in the 1950s; an initial annual output of approximately 1.5 million metric tons was generated. Global production had increased to 360 million tons by 2018, and this figure continues to rise.² Although the cumulative human production of plastics has surpassed 10 billion tons to date, almost half of that amount represents plastic waste resulting from unsatisfactory disposal and recycling practices, thus contributing substantially to environmental pollution via harmful solid waste.^3-5 Large plastic debris will eventually decompose into smaller particles, with fragments smaller than 5 mm classified as "microplastics.”^5,6

As part of the methodology, the research team examined key variables such as polymer risk, pollution load index, and the ecological risk indexes. The results from this research showed that the concentrations of microplastics in the study area's surface water ranged from 5.0 to 18.2 items/L. Furthermore, the microplastic content in the Tuojiang River valley was greater than that in the Minjiang River valley. Microplastics were mostly transparent or yellow, and predominantly occurring as granules, fragments, and fibers, with sizes mainly below 1000 μm. In 2021, the main types were polyethylene terephthalate (34.2%) and polyethylene (20.7%). Polyamide (32.8%) and polyethylene (19.5%) became the predominant types in 2023, which indicated a major change in the composition. Also, the risk of contamination through microplastics was significantly influenced by the type of polymer.¹

“These findings,” the authors of the study write,¹ “provided a theoretical foundation for the detection and risk assessment of microplastics in surface waters within the Chengdu region. In natural aquatic environments,” they continue,¹ “microplastic contaminants not only impact the aquatic ecosystem but also potentially pose threats to human health. Therefore, enhancing the risk assessment metrics for microplastics to gain a more comprehensive understanding of their adverse effects is a critical focus for future research.”

The researchers also emphasized that long-term microplastics monitoring projects should start as soon as possible.

“It is imperative,” the authors conclude,¹ “to initiate long-term microplastics monitoring projects at the earliest opportunity. Such initiatives will facilitate a comprehensive assessment of the cumulative effects and temporal trends of microplastics in the environment, thereby enhancing our understanding of their persistence and potential risks to both environmental and human health.”

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References

1. Chen, J.; Chen, Y.; Peng, X. et al. Preliminary Study on the Distribution and Risk Assessments of Microplastic Pollution in Surface Water in Chengdu, China. Sci Rep. 2026. DOI: 10.1038/s41598-026-41638-5
2. Plastics - The Facts 2019. Plastics Europe website 2019. https://plasticseurope.org/knowledge-hub/plastics-the-facts-2019/
3. Plastics - The Facts 2018. Plastics Europe website 2018. https://plasticseurope.org/knowledge-hub/plastics-the-facts-2018/
4. Thompson, R. C.; Swan, S. H.; Moore, C. J. et al. Our Plastic Age. Philos Trans R Soc Lond B Biol Sci. 2009, 364 (1526), 1973-1976. DOI: 10.1098/rstb.2009.0054
5. Cózara, A.; Echevarría, F., González-Gordilloa, J. I. et al. Plastic Debris in the Open Ocean. Proc Natl Acad Sci USA. 2014, 111 (28), 10239-10244. DOI: 10.1073/pnas.1314705111
6. Geyer, R.; Jambeck, J. R.; Law, K. L. Production, Use, and Fate of All Plastics Ever Made. Sci Adv. 2017, 3 (7), e1700782. DOI: 10.1126/sciadv.1700782
7. Thompson, R. C.; Olsen, Y.; Mitchell, R. P. et al. Lost at Sea: Where is All the Plastic? Science 2004, 304 (5672), 838. DOI: 10.1126/science.1094559