Exploring patterns in microplastic pollution in a large rural watershed

Microplastics are a ubiquitous contaminant, and their movement through freshwater systems is an understudied part of the "plastic cycle." We collected monthly surface water samples from 16 sites in an agriculturally dominated watershed, the Flint River, in southwestern Georgia to assess spatial and temporal variation in the composition and concentration of microplastics in a river system. The samples were sieved, digested in H₂O₂, and vacuum filtered onto filters for microplastic counting and morphological classification. Generalized linear models were built to investigate relationships among plastic concentration and morphology, land use variables, discharge, and physiochemical properties. All sites had detectable concentrations of microplastics, and the mean concentration (No./L ± SD) was 1.64 ± 2.17. Soluble reactive phosphorus was our strongest predictor of microplastic concentration, with measures of suspended particles also significantly explaining microplastic concentration. This research builds upon the findings of others to suggest that plastic may behave similarly to other particles. This work also documents that microplastics can be commonly found in agriculturally dominated rural watersheds with low human population densities.