Fingerprinting microplastics: A high-resolution framework for aquatic sediment contamination and degradation

This study delivers a high-resolution analysis of microplastic (MP) contamination across eight strategic sites using an integrated multi-step protocol. The optimized analytical protocol was a sequential, multi-stage process designed for maximal recovery and high-resolution characterization of microplastics. The recovered particles then underwent a rigorous, high-resolution granulometric analysis via a cascade of standardized sieves (2 mm to 63 μm), enabling precise particle size distribution profiling combined to density separation using various saline solutions, enabling the capture of particles down to 1 μm after pre-sieving through a 2-mm mesh, followed by size fractionation using a standardized sieve cascade from 630 to 63 μm; the <63 μm fraction was subsequently recovered on 1-μm membrane filters, allowing characterization down to 1 μm. Results revealed a non-uniform distribution of microplastics (MPs), with site OH14 showing the highest observed microplastic abundance among the sampled stations exhibiting the highest particle count (265 particles) and a dominance of larger fragments and microfilaments indicative of a primary discharge point. Morphological analysis showed a widespread dominance of microfilaments, particularly at OH14 and OH7, pointing to chronic contamination from domestic wastewater, while fragments and films at sites like OH1 indicated significant secondary pollution from macroplastic degradation. Chromatic profiling shows that RI16 is characterized by valuable, vibrant colors, whereas the finest fractions (63 μm–1 μm) at OH7 and OH4 consist primarily of colorless particles. This study indicates that MP pollution is a multi-source issue governed by site-specific factors such as hydrodynamics and proximity to urban zones. This study provides a high-resolution map of microplastic (MP) contamination, highlighting a highly heterogeneous and location-specific pollution profile.