Watershed Characteristics Affect Microplastic Concentrations in a Central Illinois Urban Stream

Microplastics have become an increasingly pervasive problem in many aquatic ecosystems. To date, most microplastic research has focused on marine systems as well as larger lakes and rivers. Studies conducted in the Chicago, Seine, and Danube Rivers found the mean microplastic concentrations to be: 1.94 microplastics per m 3 , 30 microplastics per m 3 , and 0.32 microplastics per m 3 , respectively. We investigated the microplastic concentrations and types in a small urban stream and its tributaries in Bloomington, Illinois. Sugar Creek has an average discharge of 60 cubic feet per second. We also considered the relationship between watershed characteristics, such as the size of watersheds, and microplastic concentrations. The area of watersheds in this study ranged from 8.3 km 2 to 15.1 km 2 . GIS methods were used to determine other characteristics such as the percentage of impervious surfaces in the watersheds. Samples were collected in the fall and winter to see if seasonality affects microplastic content. Grab samples were collected from Sugar Creek and respective tributaries. The samples were processed following guidelines on microplastic analysis created by the NOAA. We discovered that microplastic concentrations in a small urban stream can be orders of magnitude greater than those found in larger rivers. The main stream sites had an average concentration of 122 microplastics per m 3 while the tributaries had an average of 95 microplastics per m 3 . Land use and seasonality is expected to influence the types and concentrations of microplastics. Our results indicate that urban landscapes may be major contributors of microplastics in freshwater environments.