Hydrologic controls on the accumulation of different sized microplastics in the streambed sediments downstream of a wastewater treatment plant (Catalonia, Spain)

Abstract Wastewater treatment plants (WWTPs) act as a point source of microplastics (MPs) to freshwater ecosystems. Although MP abundance has been linked high-density population areas, the mechanisms how river hydrodynamics and particle size influence accumulation in streams are still largely unknown. This study investigated spatial distribution MPs within streambed sediments downstream WWTP effluent Cànoves stream (Montseny, Catalonia) during baseflow conditions. concentrations from an upstream control site were compared bypass that added untreated wastewater at times when discharge exceeded capacity. The 450 m section consisted three geomorphically altered sub-reaches interspersed between unaltered buffer sub-reaches, each ∼75 provided range hydrologic Measurements characteristics, hydrogeomorphic variables, fine particles simultaneously taken. quantified following Nile red fluorescence method for large (>64 µ m) small (10–64 particles. sediment samples mainly fragments with higher (85 particles/g sediment) vs (9 sediment). While decreased distance source, increased. Furthermore, area WWTP. most abundant bypass, suggesting these infrequent inputs storm events represent important stream. Higher coincided increased organic matter content smaller grain sizes. Overall, our results present significant findings could help explain differences transport patterns their retention streambeds, combination preferential filtration sediments, fragmentation larger