Tracking microplastics and the associated ecological risk in the southwestern Pacific Ocean

In this work, we assessed microplastics (MPs) along an ∼1000 km oceanographic transect of the Southwestern Pacific coast. This study records the environmental fingerprint of microplastics (MP) at six river mouths, from Puerto Mott in the south to the Biobío River in the central region of the Chilean coast. Superficial water was sampled in summer (2024) using a manta trawl, and the plastic particles obtained were quantified and characterized physically (size, color, shape) and chemically by Fourier Transform Infrared Spectroscopy (FTIR) and μFTIR. The results showed plastic particles at all sampled sites, ranging from ∼9000 to ∼115,000 particles km^-2 (mean: ∼29,000 ± 28,424). Notably, a clear decreasing MPs trend was observed from southern sites (S2, Maullín: ∼85,000) to the central region (S6, Biobío: ∼21,000). The prevalent characteristics of the particles found were fiber (>80 % at all sites), black (20-60 %) and blue (20 %-40 %) colors, and small sizes (smaller than 2.5 mm were >50 % in all sites). The prevalent polymers were terephthalate polyethylene (PET: 12-45 %) and polyethylene (PE: 11-25 %). Interestingly, the polymer pattern found in each site suggests a clear chemical signature of industrial activities in the area, which is likely also influenced by river discharges. In addition, an ecological risk assessment revealed that the MP levels found can be considered hazardous. These findings provide the first evidence of microplastics along the coast of central-southern Chile. Further studies are needed to evaluate the impact of the Pacific Ocean and its biodiversity.