Variation in the presence and abundance of anthropogenic microfibers in the Cumberland River in Nashville, TN, USA.

Anthropogenic microfibers (thread-like pieces of litter < 5 mm in size) including microplastic fibers have been suggested to pose a growing threat to urban rivers across the world. However, in most urban rivers, we have a limited understanding of how anthropogenic microfibers vary in presence and abundance over time. In this study, we examined how the presence and abundance of anthropogenic microfibers varied in the Cumberland River in Nashville, TN, a growing city with more than one million residents. To measure anthropogenic microfibers, we collected grab samples of surface water weekly from three locations along the Cumberland River in Nashville, TN (one upstream of the city, one in downtown, and one downstream of the city), over a 7-week period in summer of 2018 (n = 151 total samples). We found that anthropogenic microfibers were present at all study sites over time (mean of all samples = 27.9 microfibers/L) and that the mean abundance of anthropogenic microfibers significantly increased in the city and downstream of the city relative to our upstream collection site. In addition, we found that anthropogenic microfiber abundance was significantly variable over time (sample values ranged from 0 to 195 pieces/L) and that multiple factors including the presence of wastewater treatment plants may be contributing to the abundance and distribution of anthropogenic microfibers in this urban river.