Sun-damaged plastic attracts and holds positively charged particles

Jim Crocker
22nd November, 2025

Sun-damaged plastic attracts and holds positively charged particles

Scanning electron microscopy reveals that UV degradation significantly reduced the size of polyethylene particles, while polyethylene terephthalate particles exhibited minimal change in size.

Image adapted from: Bartnick et al. / CC BY (Source)

Key Findings

  • This study, conducted in a lab setting, investigated how sunlight alters the surface of common plastics (PE and PET) and their potential impact on soil
  • PE significantly breaks down with UV exposure, shrinking dramatically and forming potentially harmful nanoplastics, while PET shows much slower degradation
  • Degraded PE becomes more reactive in soil, exhibiting a capacity to bind ions – important for plant nutrients – though still less than clay, especially in alkaline conditions
Plastic pollution is a growing global concern, with plastics accumulating not just in oceans but also in soils. While much attention focuses on the sheer volume of plastic waste, less is known about how plastics change once they enter the environment and how these changes affect ecosystems. A recent study conducted by researchers from the University of Bayreuth, the Leibniz-Institut für Polymerforschung Dresden, and the National Research and Innovation Agency (Indonesia)[1] investigated how exposure to sunlight – specifically ultraviolet (UV) radiation – alters the surface properties of two common plastics, polyethylene (PE) and polyethylene terephthalate (PET), and how these alterations might impact their behaviour in soil. The study addressed a critical gap in understanding. We know microplastics – tiny plastic particles less than 5mm in size – are entering soils through various routes, including the application of compost[2][3]. However, simply knowing they are there isn’t enough. The way these microplastics interact with the soil – their reactivity, their ability to bind with other substances – depends heavily on their surface characteristics. These characteristics are influenced by the type of plastic and how long it has been exposed to environmental factors. Researchers exposed PE and PET particles, initially sized between 200-400 micrometers (µm), to simulated sunlight using accelerated UV degradation. They then meticulously tracked changes in particle size, surface structure, and chemical composition. Particle size was measured using electron microscopy, a technique that allows for highly magnified images of the plastic surfaces. Surface charge parameters, like zeta potential (a measure of the electrical charge on the particle surface) and cation exchange capacity (the ability to attract positively charged ions), were assessed at different pH levels. Finally, techniques like Fourier transform infrared spectroscopy and X-ray photoemission spectroscopy were used to identify changes in the chemical bonds and atomic composition of the plastic surfaces. The results revealed a significant difference between PE and PET. PE particles underwent substantial degradation, shrinking dramatically in size – from an average of 375 µm to just 8 µm after 2000 hours of UV exposure. PET particles, however, showed only a modest size reduction, decreasing from 653 µm to 484 µm. This difference in degradation rate was accompanied by changes in surface properties. The degraded PE particles exhibited a greater electrical charge and a lower isoelectric point (the pH at which the surface has no net electrical charge). Crucially, the degraded PE surface became unstable in alkaline (high pH) conditions, indicating the formation of new chemical groups – specifically carbonyl groups – and an increase in its ability to attract water (hydrophilicity). PET showed fewer chemical changes overall. The most striking finding was the increased reactivity of degraded PE in soil. The study demonstrated that degraded PE could exhibit up to one-tenth the cation sorption power of clay – a key component of soil – in alkaline environments. Cation sorption is the ability of a material to bind positively charged ions, which are essential nutrients for plant growth. Degraded PET, however, remained relatively inert. This research builds upon earlier work highlighting the ubiquitous presence of microplastics in agricultural soils, often introduced via compost application[3]. While previous studies have quantified the amount of microplastics entering soils, this study begins to explain how those microplastics might behave once they are there. The findings suggest that PE, a commonly used plastic in packaging and films, poses a greater potential risk to soil ecosystems due to its susceptibility to UV degradation and subsequent increase in reactivity. The fact that compost application may contribute only a small percentage of total microplastic stocks[3] underscores the importance of understanding all input pathways, including littering, and the subsequent environmental fate of these materials. The study emphasizes the need for further research to differentiate the effects of various plastic types on soil ecosystems. The differing behaviours of PE and PET highlight the importance of considering the specific polymer composition when assessing the environmental impact of plastic pollution.

EnvironmentSustainabilityBiochem

References

Main Study

1) UV-degraded polyethylene exhibits variable charge and enhanced cation adsorption

Published 21st November, 2025

https://doi.org/10.1371/journal.pone.0337180

Related Studies

2) The plastic in microplastics: A review.

https://doi.org/10.1016/j.marpolbul.2017.01.082

3) Microplastic contamination of soil: Are input pathways by compost overridden by littering?

https://doi.org/10.1016/j.scitotenv.2022.158889


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