Watershed urbanization and sanitation as predictors of microplastic contamination in stream sediments.

Urbanization represents a major land-use change with substantial impacts on stream ecosystems. Urban streams are exposed to a wide range of contaminants, including microplastics (MPs), which enter these systems primarily through wastewater and stormwater runoff. However, the effects of urbanization and sanitation coverage on MPs accumulation in subtropical streams remain poorly understood. This study examined the influence of urbanization intensity and sanitation coverage on MP accumulation in sediments from 16 urban streams across five cities in Uruguay, representing a gradient of urbanization and access to sanitation. Higher MP abundances were observed in sediments from streams under greater urban pressure, whereas MPs levels decreased with increasing proportions of households with access to sanitation. Polymer composition was dominated by polyethylene and polypropylene, which are commonly associated with domestic and urban waste. PERI provided a comparative ranking among the sampled streams but should not be interpreted as a measure of actual ecological risk. These results emphasize the need to consider both the degree of urbanization and inequalities in access to services such as sanitation. In addition, the findings highlight the importance of including emerging contaminants such as MPs in comprehensive environmental assessments. This evidence can support the development of public policies aimed at mitigating the impacts of urbanization on aquatic ecosystems and promoting equitable and sustainable territorial management.