Abstract

The coastal wetlands of the Chilo ́e Archipelago in Chile (42◦28′04.2“ S, 73◦32’21.8” W), which serve as important habitats for migratory birds, are increasingly exposed to anthropogenic pressures, particularly from nearby aquaculture activities. The chemical composition of microplastics and associated particles was analyzed using confocal micro-Raman spectroscopy without visual pre-selection to determine the spatial distribution of microplastics and to test the hypothesis that the microplastics in the sediment originate from the fragmentation of fishing gear. For this purpose, surface sediment samples (0–2 cm) were collected from six transects, three tidal heights with three replicates each per sampling site. The particles were separated by digestion with hydrogen peroxide, then separated by density flotation with zinc chloride and vacuum-filtered. Quality controls were performed, and extraction efficiency was estimated by enriching the sediments with fluorescent particles. A total of 550 particles in 54 filters were analyzed. The results showed high heterogeneity, with a predominance of fibers and fragments of microplastics, cellulose-containing materials, pigments, and/or paint particles, followed by inorganic particles. A total of 43 microplastic particles (46.5%) and fibers (44.2%) were identified, primarily polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyamides (PA) (83.8% of the total microplastics). The concentration of microplastics was 137 particles per kg of dry sediment, a value lower than published values measured near mussel farms. Microplastic distribution in intertidal sediments is spatially structured by sediment grain size and local geomorphological features, highlighting the role of sedimentary heterogeneity in shaping contaminant accumulation patterns. A comparison of the Raman spectra of micro- plastics in the sediment with fragments of mussel farming gear and reference libraries revealed a high spectral similarity (HQI > 85%), suggesting that the degradation of aquaculture equipment could be one of the sources contributing to microplastics in the sediment.