Land Use Pattern Affects Microplastic Concentrations in Stormwater Drains in Urban Catchments in Perth, Western Australia

Stormwater drains act as important vectors for microplastics, enabling the transportation of microplastic polymers from terrestrial systems where they are produced and consumed to aquatic and marine ecosystems. In this study, microplastic concentrations and their size fractions were measured in six stormwater catchments in the Perth and Peel region of Western Australia. Stormwater drains with contrasting land uses and catchment characteristics were selected and two sites along each drain were sampled. Water samples were filtered in situ with a purpose-built fractionation device. Catchment boundaries and contributing drainage areas were derived from a hydrologically enforced digital elevation model. Microplastic concentrations within the sites varied from 8.8 to 25.1 microplastics/L (mean 14.2 microplastics/L). Fibrous microplastics were the most common morphology, followed by fragments. Polymer types identified using Raman spectroscopy included polypropylene (64.6% of samples), polyethylene (64.7%), polytetrafluoroethylene (5.9%) and polyvinylidene fluoride (5.9%). There was no statistically significant variation in microplastic concentrations across or within stormwater catchments. A linear mixed-effect model showed that several components of the land use pattern: catchment area, catchment population, and the proportion of industrial land, natural land and public open space, were positively related to microplastic concentrations. The proportion of residential land was negatively related to microplastic concentrations. The lack of significant variation in microplastic concentration observed both across and within the catchments points to their ubiquitous presence in stormwater systems in the region. This study is the first to examine microplastic contamination in the water of stormwater drainage systems in Perth, Western Australia. These stormwater systems contain considerable concentrations of microplastics, confirming their importance as transport mechanisms for plastics into aquatic and marine ecosystems.