Anthropogenic Macroscale and Microscale Debris (Including Plastics) Have Differing Spatial Distributions Across a Small Urban Watershed

Anthropogenic litter in the environment is a globally pervasive contamination issue with harmful impacts on human and ecological health from exposure to both macroscale (≥5 mm) and microscale (<5 mm) litter. To assess the prevalence, distribution, and drivers of plastic and nonplastic litter in the environment, we assessed anthropogenic litter abundance and characteristics at 10 sites across an urban catchment (Deer Creek near St. Louis, MO) in October 2022. Macroscale litter was evaluated within the channel bed, and stream water and sediment were sampled to assess anthropogenic microparticle content. The abundance of all macrolitter types ranged from 0.03 to 1.42 counts/m2, while plastic macrolitter ranged from 0.00 to 0.61 counts/m2. Plastic films (e.g., bags) were the most common (34.7%) type of plastic macrolitter that we found. Microparticles in water were below the limit of detection at all sites, while in sediment they had concentrations ranging from below the limit of detection to 84.28 counts/kg (with confirmed detections at 6 of 10 sites). Macroscale and microscale litter abundances across the watershed did not correlate, suggesting different sourcing and distribution drivers for the two debris size categories. Macroplastics correlated strongly and positively with impervious surface area and stream discharge, implying a combined influence of land use and hydrology on their deposition. Our findings suggest that the relationship between macroscale and microscale litter might vary depending on local sourcing and transport mechanisms.