Developing a method to identify tyre particles by detecting benzothiazole via GC-MS

Tyre particles are a dominant source of microplastic pollution in our environment. However, their chemical and physical properties are poorly understood and no standardised methods for identifying and quantifying them exist. This study looked to develop a method to identify tyre particles using two tyre samples of differing particle sizes, fine (62 - 125 µm) and coarse (250 – 500 µm). Both samples underwent ultrasound-assisted extraction before being analysed via gas chromatography-mass spectrometry (GC-MS) in both full scan and SIM mode, using benzothiazole as a marker. Both samples were also analysed via particle size analysis, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) in order to determine their chemical and physical properties. Particle size analysis was found to be inaccurate with greater particle size ranges than those expected being reported. SEM showed that the particles were elongated in shape with visible mineral encrustations containing a range of elements. The FTIR spectrum for each sample showed characteristic peaks for natural rubber and the polymers styrene-butadiene rubber (SBR) and ethylene propylene diene monomer (EPDM). The method successfully extracted benzothiazole from the tyre samples but only SIM mode was able to detect benzothiazole in both samples. Other issues with the method were discovered, including the method being determined semi-quantitative, a low recovery being achieved (27%) and the peak shape being suboptimal with visible tailing being present. Benzothiazole was found to be present in a significantly greater quantity in the coarse sample (0.00180 ± 0.000220 mg g-1) than in the fine sample (0.00102 ± 0.000238 mg g-1). With tyre particles being present in the environment at sizes less than 250/300 µm, these results suggest that the need for sensitive analytical techniques is a potential challenge for identifying and quantifying tyre particles in the environment. Overall, this straightforward method shows promise. The application of some simple adaptations should allow this method to become more accurate and fully quantitative, and it should help to fill the gap that exists of a lack of suitable analytical techniques currently available to detect and quantify tyre particles in the environment. This method could thus provide a greater understanding of the issue of environmental tyre particle pollution and its impacts, which could be used to inform policy and regulations on tyre particles and microplastics.