Microplastic accumulation in benthic macroinvertebrates is widespread, regardless of the river ecological status

Microplastics accumulation in freshwater organisms is expected to rise with the level of urbanization occurring near riverbanks, although other factors also contribute to this trend. Benthic macroinvertebrates, in particular, may be disproportionately affected by microplastic accumulation due to their feeding strategies (e.g., filter vs deposit feeders), highlighting feeding type-specific ingestion patterns. Nevertheless, it remains uncertain whether these impacts translate into detectable changes at the community level, underscoring the need for in situ investigations. We quantified the accumulation of microplastics in Chironomidae and Oligochaeta across 15 stream reaches along a rural-urban environmental gradient, within 3 Northern Atlantic rivers in Portugal. Microplastics were detected in organisms regardless of their river's Ecological Quality Status, suggesting that the impact of urban land use is not the only factor that drives microplastics at a local scale. We also found microplastics across different Chironomidae subfamilies and tribes belonging to different functional feeding groups, potentially facilitating a higher influx of microplastics into the aquatic food web. This study demonstrates that even well-maintained ecosystems are not immune to microplastics pollution, emphasizing the urgent need for enhanced research efforts to develop methods for more effectively assessing and mitigating the impacts of microplastics on aquatic organisms.