Project Description: 

This proposed project aims to identify the transport and mitigation of tire and road wear microparticles in highway stormwater runoff. We will mainly focus on tire wear microplastics containing 6-PPD.  The composition of the tire is a chemically complex and heterogeneous mixture having about 5–10% additives required for its stability and durability. Therefore, a tire can contain as many as 200 various additives. That can be leached from tire and road wear particles (TRWPs) into the aquatic environment. Although predicting material leachability from tires and their subsequent potential risk for the ecosystem was indicated in the early nineties, very few studies have been reported investigating TRWP leachates. Very recently, a study has published an oxidation product of tire antioxidant N-(1,3-dimethylbutyl)-N′-phenyl-pphenylenediamine (6-PPD), 6-PPD-quinone, as the lethal cause of coho salmon mortality(1).  6PPD quinone (the transformation product of 6PPD) has been reported in roadway runoff, tire rubber leachates, and road dust. Although very little information exists regarding the occurrence and fate of 6PPD quinone in the environment, this chemical is assumed to be present in surface waters globally because of the widespread use of the parent compound. The toxicity of 6PPD quinone could be a global threat to aquatic species and may not be limited to coho salmon only. 

_{Figure 1. Overall schematic of project.}

Scope of Work: This will continue our current project for Year 2. We will accomplish the goal of this project through four tasks. We have already finished Task 1 and Task 2 and started Task 3. In Year 2, we plan to finish Task 2 by 7/31/2024 and Task 3 by 12/31/2024. We plan to begin Task 4 from 01/01/2025.

• Task 1.  Literature Review  (completion date: 03/31/2024) 
• Task 2. Measurement of Tire and Road Wear Microparticles in Stormwater  (Completion date: 07/31/2024)
• Task 3 . Experimental Approaches for Mitigation Strategies (50% complete; expected end date: 12/31/2024)
• Task 4. Modeling Approaches for Mitigation Strategies (estimated start date: 01/01/2025; estimated end date: 05/31/2025)

US DOT Priorities: The study effort aligns with the USDOT's dedication to sustainability and environmental preservation. The study advances knowledge about tire wear debris in the environment by examining the stability and removal of tire particles in water bodies. This information is essential for creating mitigation plans that work and encouraging environmentally friendly transportation behaviors. This study's results can influence policy choices and direct the creation of affordable mitigation infrastructure for this emerging pollution. The proper filtration media can be integrated into existing roadside structures, such as roadside shoulder, which will ultimately help create a more sustainable transportation system.

Outputs: Our technical deliverable will make recommendations concerning the types of best management practices (BMPs) and mitigation measures needed to remove tire and road wear microparticles containing 6-PPD as well as the resulting oxidized 6PPD-quinone potentially present during stormwater flows. 

Outcomes/Impacts: The research investigated the transport and removal of tire particles in various water bodies. The rate of aggregation and the zeta potential were measured in different synthetic water samples (Figure 2a). It was discovered that tire particles exhibited minimal aggregation in most aquatic environments including stormwater. High mobility of tire particles poses a significant environmental concern due to their widespread distribution. 

_{Figure 2: Findings from Task 2 and Task 3 show the lack of aggregation of tire wear particles in stormwater in Figure1a. Figure 1b presents the filtration pattern of tire wear particles through sand filter. Zn was used as marker for tire wear particles.}

Filtration of tire wear particles on the roadside shoulder was identified as a possible solution. Column filtration experiments were conducted. However, removing tire particles through filtration using a white quartz sand column was inefficient in the preliminary studies (Figure 2b). These findings highlight the need for developing more effective strategies to mitigate the environmental impact of tire wear particles. Based on these findings, we will explore additional filtration media for removal of tire wear particles from stormwater.