Plastic additives as tracers of microplastic sources in Japanese road dusts

Plastic waste and microplastic pollution has been reported around the world. Up to 80% of marine plastic debris is derived from land, thus it is important to identify the terrestrial sources of microplastics to reduce their environmental impact. In this study, the abundance and polymer type of microplastics were characterized for road dusts collected from Kumamoto, Okinawa, and Tokyo, Japan. In addition, the profiles of additives in plastic products on the road and in road dust microplastics were determined to evaluate the potential use of additives as chemical tracers of microplastic sources. The abundance of microplastics in road dusts was 96 ± 85 pieces/kg (dry wt.) (n = 16), 68 ± 77 pieces/kg (n = 12), and 230 ± 50 pieces/kg (n = 8) in Kumamoto, Okinawa and Tokyo, respectively. In Kumamoto and Okinawa, significant correlations were observed between total microplastic abundance in road dusts and daily vehicle traffic. In Tokyo, high population and traffic density may account for the greater abundance of microplastics in road dusts than in the other cities. Polymer analysis shows that poly (diallyl phthalate), polyvinyl chloride, polymethyl methacrylate and polyester accounted for 60% to 70% of the total microplastics analyzed. To determine the potential sources of microplastics, plastic additives were analyzed in road dusts and fragments of road marking from the study area. Five common additives including plasticizers and flame retardants were identified in both road dusts and road markings. This suggests that road markings are a significant source of microplastics in Japanese road dust, and that additive profiles in plastic samples may be suitable tracers for determining the sources of microplastics in road dust.