Fluvial Concentrations of Microplastics in a Suburban Micro-Watershed: Sampling Methodology and Analysis

Plastics have been incorporated into everyday life due to their versatility, yet when microplastic particles enter natural fluvial systems, they pollute the surrounding environment and pose potential human health risks. As state and federal agencies develop regulations for microplastics in natural systems, it is important to properly assess potential sources of pollution and the concentration of microplastic particles in freshwater environments; however, microplastic pollution in small streams can be complex to investigate because of their dynamic hydrography and lack of standardization in microplastic sample collection and quantification. In this study, a unique low-cost sampling station was designed to collect microplastics from surface water in a shallow urban freshwater stream. The goal is to understand the variation in microplastic concentrations across a watershed at baseflow. Surface water samples were collected and analyzed from five sites along Hunnicutt Creek, a suburban freshwater stream located in Clemson, SC. The sampling station was deployed in the upper water column long enough to allow 10 m3 of surface water through a sampling net. Seven sampling events occurred at five sampling sites across the Hunnicutt Creek watershed. Surface water samples indicate that the microplastic abundance increased from the top of the watershed (269 ± 30 particles/10 m3) to the bottom of the watershed (715 ± 93 particles/10 m3). Fibers were the dominant morphology identified in the system, which accounted for 99.7% of the microplastic particles sampled. There was a significant difference in the microplastic concentrations between sampling sites moving down the watershed (F = 53.27, df = 4, p < 0.001), with the highest concentrations at the bottom of the watershed (or at the confluence of the tributaries). This work contributes to the understanding of how microplastics move at low-flow/baseflow conditions in small freshwater streams, which are common throughout global communities.