Microplastics from road markings in the presence of tyre wear – a laboratory test method development

Road markings were reported as meaningful contributors to microplastic pollution, but recent field research indicated that the prior theoretical calculations overestimated the emissions by order of magnitude. The absence of a dependable laboratory test method to distinguish road markings wear from tyre wear was hindering studies of this topic; while larger particles of road markings could be distinguished based on the embedded glass beads, smaller fragments could not be reliably separated and apportioned. We report development of analytical procedure, comprising temperature gradient method and inductively coupled plasma optical emission spectroscopy, as suitable to distinguish between the tyre and road marking wear. To validate it, road marking samples with known composition were subjected to testing at wear simulator. Periodically, various road markings were evaluated for retroreflectivity and wear and the abraded residue was collected and analysed. Good correlation was found between the extent of abrasion and the measured emissions. Amongst noteworthy results are also: (1) enormous dissimilarities between different materials – between 70 and ¿6000 revolutions of the wear simulator were needed before microplastics release commenced, and (2) the protective role of glass beads – as long as they were present, no meaningful abrasion of the paint layer was occurring and the quantity of collected microplastics was negligible. The previously suggested use of retroreflectivity decrease below a threshold value as an indicator of possible emissions was not fully sufficient because in some cases the glass beads were damaged but not extracted from the film; in addition, it was not reliable in case of thermoplastic road markings that are designed for slow abrasion during usage. The finding related to the differences in service life of various road markings and the protective role of glass beads emphasise the need to select appropriately durable materials and the necessity to maintain them appropriately. Also see: https://micro2024.sciencesconf.org/551418/document