Tire and road wear particles (TRWP) are created through the friction between tires and the road surface. These particles are considered a major source of microplastics (MPs) to the environment. For example, an annual release of 19,000 tonnes of MPs from land-based sources is estimated for Norway, 40% of which are considered to be TRWP (Sundt et al., 2021). While the application of speed limits and an optimal tire pressure can reduce the production of TRWP, the use of studded tires and a heavy car weight can increase the tire wear (Rødland et al., 2022).
As for other plastic polymers, additive chemicals are used during the production of tires and can leach out and enter the environment. On average, over 400 organic chemicals are identifiable in a tire (EmissionsAnalytics, 2023). Examples of such chemicals include the antioxidant and antiozonant 6PPD (N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine), one of its transformation products 6PPD-Q (6PPD-Quinone) and the crosslinking agent HMMM (Hexa(methoxymethyl)melamin). Naturally, concentrations of these chemicals are particularly high in compartments strongly influenced by road traffic, such as road run-off and recipient waters. The presence of tire related additive chemicals has been reported in urban streams (Johannessen et al., 2022), wastewater treatment plant effluents (Seiwert et al., 2020), road run-off (Challis et al., 2021) and marine sediments (Zeng et al., 2023), among others. Recently, 6PPD and 6PPD-Q have also been detected in three fish species, indicating their occurrence in wildlife for the first time (Ji et al., 2022).
Cold-climate regions have been identified as being particularly prone to contamination by tire related additive chemicals due to several factors: the common use of softer winter tires and the use of studded tires, both increasing the production of TRWP, bad road conditions due to the harsh climatic conditions and the use of road salts (Challis et al., 2021). Furthermore, it has been shown that the presence of road salts can enhance the toxic effects of 6PPD, as is the case for the rotifer Brachionus calyciflorus (Klauschies & Isanta-Navarro, 2022). Therefore, screening for tire related additive chemicals in these regions will offer valuable information on the current state and potential actions that might need to be taken to reduce the risks for the environment. The Nordic countries have stated their willingness to actively investigate and manage this challenge, e.g. by assessing the different possibilities to reduce the release of MPs from tire wear (Furuseth & Rødland, 2020) and by initiating the study that is presented here.