It's complicated: the relationship between urban features and aquatic plastic pollution

Estimates suggest millions of metric tonnes of plastic enter aquatic ecosystems annually, with urban environments acting as a primary source of this leakage. Within cities, waterways such as rivers, streams, and canals act as arteries to collect and transport land-based plastic waste outside the city boundaries. While the source of cities for aquatic plastic pollution is clear, the understanding of processes governing the journey of plastic through cities and the drivers of transport and accumulation within cities is limited. Here, we characterize the baseline patterns of floating plastic by mapping the spatial distribution and temporal variability of plastic accumulation and transport across Amsterdam, by using a database of nearly 10,000 monitored plastic items with monthly monitoring sessions between November 2022 and October 2023. Plastic accumulation and transport are neither uniform in space nor constant in time. We further identify and explore the explanatory power of site-specific urban features that may drive plastic abundance at the local level. We reduced 87 urban environmental features to 8 principal components, which describe unique gradients in the urban landscape. By correlating these principal components with our plastic observations, we identify that spatial patterns differ substantially between the accumulation of plastics and the transport of plastics. Some plastic types are widely distributed across multiple urban gradients, where others are strongly associated with specific urban contexts. Most plastic types show no significant correlations, highlighting the complex nature and ubiquity of plastic in all urban contexts. We highlight that item-specific data is necessary to disentangle the complex nature of urban plastic pollution. By analyzing which items tend to co-exist, potential clustering of items, and their abundance in the context of specific urban features, we are getting closer to detecting the true sources and drivers of urban plastic pollution.