Characterization and temporal variation of microplastics in surface waters and sediments of the lower Lurín River...

Microplastics (MP) are a major concern for aquatic ecosystems due to their widespread presence and biological impacts. The lower Lurín River basin is particularly vulnerable due to wastewater discharges and solid waste pollution. This study analyzed MP contamination in surface water and sediments at four points during the dry and wet seasons. Raman spectroscopy was used on representative samples to validate visual identification and confirm chemical composition. MP were identified in surface waters (median: 0.24 items/m³; range: 0-0.67) and sediments (median: 20 items/kg; range: 0-80). Spectroscopic analysis confirmed the presence of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), and cellulose, supporting the visual classification. White was the most frequent color in both surface waters and sediments (64.3% and 42.9%, respectively). Fibers were the prevalent morphology (>60%), followed by fragments in water (26.2%) and films in sediments (17.9%). A significant difference in MP abundance was found in sediments (H = 8.305; p = 0.040) between point P1 (closest to the mouth) and P4. In surface water, a negative correlation was observed between precipitation and MP abundance (rs = -0.649; p = 0.004), suggesting a dilution effect. No significant seasonal differences were detected in water (p = 0.310) or sediments (p = 0.791). These results may have been influenced by the 2023 El Niño event, which increased precipitation during the traditional dry season.