Microplastics in the Tennessee River and Three Tributary Urban Creeks

Microplastic particles (MP) are increasingly recognized as an emerging threat to human and ecological health. Yet, surprisingly, there has been relatively little research into the abundance, sources and transportation of MP in urban freshwater ecosystems. From October 25 – December 5, 2021 we collected water samples from the Tennessee River and 3 highly urbanized tributary creeks in Knox County: Second Creek, Third Creek and Turkey Creek. Following standard protocols, water samples were vacuum filtered (0.47 μm), dried and subjected to detailed stereomicroscopic examination. In most cases, acid digestion to remove organic matter was not needed. MP was identified using standard protocols based on shape, texture, color and the “hot needle point” method whereby plastic reacts to heat. Results indicate a high abundance of MP in the Tennessee River as well as the creeks. Interestingly, MP abundance varies extensively, ranging from less than 5 to over 75 particles per liter. As with previous studies, the large majority of MP particles found in these creeks are linear fibers, ostensibly originating from washing machine outflow. Increasing MP abundance is most strongly correlated with local factors, especially proximity to runoff discharge pipes and areas of ponding and low flow where plastic debris is accumulating. MP abundance variation between the creeks and the Tennessee River does not seem to be statistically significant, again indicating the importance of local factors on MP sources and accumulation.