Efficient pretreatment method for analyzing microplastics in urban road dust containing composite materials

Tire wear particles (TWPs) and road marking paint (RMP) fragments are main sources of composite microplastics (MPs) in urban road dust and contribute significantly to the load of MPs in water environments. However, few studies have investigated the influence of organic decomposition such as cellulolytic enzyme decomposition (EZM) and Fenton (FT), on the abundance and characteristics of composite MPs in the environment. This study aimed to evaluate an organic matter decomposition method suitable for MP analysis using urban road dust containing composite materials, focusing on EZM and FT methods. The EZM has 1.1-4.5 times as high recovery of synthetic polymers as FT based on particle number. The difference in the number of orange particles was thought to be one of the factors behind this. Sodium citrate buffer used in EZM might degrade any components in the RMP-suspected orange particles and reduce the particle density to float in the NaI solution. For black tire-suspected particles, which were detected in large numbers, no significant difference was confirmed between EZM and FT in the number of these particles, but FT methods might affect the proportion of tire material in tire-suspected materials. The EZM method may be useful for quantification of composite MPs and is more suitable for analyzing samples in which there may be many RMP-suspected particles due to the characteristics of the surrounding environment or catchment area. PRACTITIONER POINTS: Tires and road marking paint (RMP) are main sources of composite microplastics (MPs) washed into stormwater from road dust. The cellulolytic enzyme decomposition is useful for analysis of composite MPs and comprehensive understanding of materials in the environment. It is necessary to select an organic matter decomposition method that suits the sample characteristics and research purpose.