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Microplastic pollution is emerging as a potential major health threat. Tiny particles of plastic are introduced into the environment from a multitude of sources and enter the human body via the air we breathe, the water we drink, and the food we eat. Initial research has linked exposure to microplastics with several serious health issues, however, as analysis of microplastics is still relatively new, reliable methods of characterizing microplastic particles are lacking, especially for the characterization of tire and road wear particles.
A new study has helped develop a reliable analytical method for characterizing tire and road wear particles using scanning electron microscopy (SEM) alongside energy-dispersive X-ray spectroscopy (EDX) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS).
Why Study Environmental Microplastic Particles?
Microplastics are being released into the environment at an increasing rate. Everyday actions such as opening a bottle of water or tearing open a plastic packet release tiny particles of plastic into the environment. It lingers in the air we breathe, enters the water supply, and even ends up in the food we consume.
As research into microplastics is fairly new, not enough data is available to conclusively say what the impact of exposure to microplastics is on human health. However, the initial data has linked microplastic consumption to a variety of health problems such as obesity, reproductive damage, developmental delays in children, cancer, and obesity. Studies have already proven that microplastics are taken up by the body’s organs and have the power to damage cells and initiate inflammatory reactions and immune responses.
Over recent years, scientists have focused on developing techniques for analyzing and characterizing environmental microplastic particles (MP) which measure 1 μm to 5 mm in size. A study of tire and road wear particles (TRWP) has emerged in the field as a priority and scientists are working to develop reliable methods of studying TRWP, a material consisting of elastomeric polymer-containing tread that is released due to the friction force between a vehicle’s tire and the road.
TRWP can remain suspended in the air, and, therefore, breathed in by people passing on the street adjacent to the road. It has also been proven to enter bodies of water. However, experts do not agree on how much of a risk this tire dust poses to human health. The Organisation for Economic Cooperation and Development (OECD) states that as much as 9 kg of tire dust is produced daily per kilometer of road used by 25,000 cars. Further research is needed to corroborate this figure and to help link levels of tire dust with health problems.
Measuring TRWP
Recent studies investigating microplastic particles in water samples have relied on particle counts to quantify the level of microplastic pollution. In terms of investigating TRWP specifically, most studies have used methodologies where the black microplastic particles (considered to be TRWP) are visually identified. However, this technique is significantly limited as not all black particles are TRWP and visual analysis cannot determine which black particles are genuinely those produced by tires.
Techniques that are most used in microplastic research, such as Raman microscopy, are not appropriate for studying TRWP because of the characteristics of the black particles that interfere with such spectroscopic techniques.
Therefore, a new effective and reliable method of characterizing TRWP is needed to further our knowledge of microplastic pollution and how it affects human health.
Establishing a New Method of Characterizing TRWP
A recent study conducted by a team of researchers across institutes in the US and Hong Kong developed a technique combining scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) mapping and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Their findings demonstrate that the newly established method is effective at identifying and characterizing individual TRWP.
Until now, no studies have put forward detailed chemical mapping techniques capable of characterizing both the elemental and organic fragment signatures specific to TRWP. For the first time, the team investigated a range of particle types such as bulk tire tread material, carbon black particles, cryogenically milled tire tread (CMTT) particles, polystyrene spheres, and TRWP generated from a road simulator using SEM/EDX and ToF-SIMS mapping.
The combination of methods allowed for individual TRWP to be determined. For example, the surface analysis revealed the presence of numerous elements that are associated with the chemical composition of tire tread material. Density separation also allowed for the calculation of the average TRWP size and aspect ratio, helping to determine the size of the particles, which may be vital to future studies investigating the impact of TRWP exposure on human health.
The current research will no doubt be essential to developing microplastic research and provides a reliable methodology for future studies that will investigate the relationship between TRWP and various health implications.
References and Further Reading
Auta, H., Emenike, C. and Fauziah, S., 2017. Distribution and importance of microplastics in the marine environment: A review of the sources, fate, effects, and potential solutions. Environment International, 102, pp.165-176. https://www.sciencedirect.com/science/article/pii/S016041201631011X
Cox, K., Covernton, G., Davies, H., Dower, J., Juanes, F. and Dudas, S., 2019. Human Consumption of Microplastics. Environmental Science & Technology, 53(12), pp.7068-7074. https://pubs.acs.org/doi/10.1021/acs.est.9b01517
Hwang, J., Choi, D., Han, S., Jung, S., Choi, J. and Hong, J., 2020. Potential toxicity of polystyrene microplastic particles. Scientific Reports, 10(1). https://www.nature.com/articles/s41598-020-64464-9
Kovochich, M., Liong, M., Parker, J., Oh, S., Lee, J., Xi, L., Kreider, M. and Unice, K., 2021. Chemical mapping of tire and road wear particles for single particle analysis. Science of The Total Environment, 757, p.144085. https://www.sciencedirect.com/science/article/pii/S0048969720376166
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