What is in specks of highway road dust? Quantification and Chemical Characterization of Small microplastics (<100 µm) and Plastic additives

Road dust is one of the environment's most important microplastic and plastic additives sources. Highway road dust (HWRD) continuously accumulates on highways due to the traffic of vehicles; it is a composite miscellany of particles, and it is considered one of the primary sources of microplastics (MPs) in the atmosphere The wear of tires, bitumen, road marking paints used in road pavement, brake wear, vehicle emissions, soil from construction sites, atmospheric deposition, plastic or other materials debris, and road pavement made of recycled plastics are generally deposited in the HWRD. In this study, a simultaneous quantification and chemical characterization of additives, plasticizers, natural and non-plastic synthetic fibers (APFs), and small microplastics (SMPs, &lt;100 µm) in HWRD will be performed. The sampling procedure was optimized, as well as pretreatment (extraction, purification, and filtration) and analysis via Micro-FTIR. HWRD samples were collected during dry periods (at least 2 weeks after a rainfall event) from winter 2021 to winter 2022 from a trafficked highway in Italy. A detailed protocol was designed to minimize potential plastic contamination of samples during sampling, transport of samples, pretreatment, and analysis. The pre-treatment procedure (oleoextraction, purification, and filtration) was optimized according to the one previously developed. The filters were then analyzed via Micro-FTIR, where identification and quantification via microscopic counting were performed simultaneously. Among the polymers characterized and quantified, vinyl ester and polytetrafluoroethylene were predominant. Lubricants and plasticizers are the two most abundant categories, followed by vulcanizing agents, accelerators, and pre-vulcanizing retarders derived mainly from tires. A potential relation between APFs and SMPs in the different seasons was observed, as their concentration was lower in summer for both and higher in winter 2022. Data from this study will be relevant in assessing the load of SMPs and APFs from highways, which is urgently necessary for a more accurate inclusion in emission inventories, receptor modeling, and health protection programs by policymakers, especially in air and water pollution policies, to prevent risks for human health.