Nile Red Microplastic Validation: Enhancing the Study of Microplastics in Oregon’s River Water

Microplastics are ubiquitous in our environment and can be found in rivers, streams, oceans, and even tap water. In Oregon, eight sites along four freshwater rivers were evaluated for the presence of microplastics. Nile Red dye was tested as a method to improve the accuracy of microplastic counts in plankton tow samples from each of the sites along the Columbia, Willamette, Deschutes, and Rogue Rivers. Samples were stratified to separate microplastics from organic debris using a hypersaline solution. All samples were analyzed using traditional light microscopy for initial microplastic counts, then Nile Red dye was applied to each filter and re-analyzed using light microscopy for a before/after comparison. The difference in microplastic counts between before and after dye application was quantified using a Wilcox Test. The Wilcox Test comparing fibers produced a p-value of 0.0675, and the test comparing particles produced a p-value of 0.0007. The count difference is significant for particles before and after dye application. Overall the trend indicates that Nile Red aided in the identification of microplastics, specifically particles more so than fibers.