Microplastic contamination across trophic levels in a lowland spring watercourse of Northwestern Italy: New insights and biomonitoring implications

Microplastic (MP) pollution is an emerging environmental threat, with freshwater ecosystems acting as both transport pathways and accumulation zones for these synthetic particles. Despite growing research, data on MP contamination in small, lowland spring watercourses remain scarce. This study investigates MP distribution in the Sacchetti Ditch, a lowland spring-fed stream in Northwestern Italy, through by-monthly sampling over one year, leading to insights about seasonal trends. MP occurrence was analyzed in water, sediment, and biotic compartments, including fish, macroinvertebrates, and bivalves. MP concentrations in water ranged from 27.2± 47.1 MP L􀀀 1 (March) to 61.2 ± 20.4 MP L􀀀 1 (May), while sediment levels peaked at 358.6 ± 224.1 MP kg􀀀 1 in January. Fragments and fibers dominated across matrices, with black, red, and blue as the most common colors. Statistical analyses revealed no significant temporal trends, suggesting continuous MP inputs from untreated wastewater discharge, urban runoff, and industrial effluents. Biotic samples confirmed MP ingestion across trophic levels. Gambusia affinis and Gammarus fossarum exhibited the highest MP burdens in winter, while Unio elongatulus showed a strong correlation with waterborne MPs. Polymer analysis identified polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polyamide (PA), with PP showing significant selective ingestion by U. elongatulus. Non-Metric Multi-Dimensional Scaling (NMDS) analysis of seasonal MP content in both biotic and abiotic samples indicated no clear seasonal patterns across trophic levels, reinforcing the role of the ditch as a long-term MPs reservoir. These findings highlight the need for urgent mitigation measures to reduce persistent MP pollution in small freshwater ecosystems.