Microplastic Contamination in Deep-Sea Sediments of the Western Pacific Mariana Trench: Distribution, Polymer Identification, and Ecological Risk Assessment

Abstract

This study presents the first comprehensive characterization of microplastic contamination in deep-sea sediments collected from the Mariana Trench at depths ranging from 5,108 to 10,908 meters. A total of 36 sediment cores were analyzed using μ-FTIR spectroscopy and micro-Raman mapping. Microplastic concentrations ranged from 185 to 2,847 particles/kg dry weight, with the highest abundance found at hadal depths (>8,000 m). Polyethylene terephthalate (PET, 38.2%), polyamide (PA, 22.5%), and polypropylene (PP, 18.7%) were the dominant polymer types. Fiber morphology accounted for 72% of all particles, consistent with textile origin. An ecological risk index analysis indicates moderate-to-high ecological risk (RI = 285-890) at all sampling stations, with heavy metal contaminants (Pb, Cd, Cu) adsorbed on microplastic surfaces detected by SEM-EDS at concentrations 5-100× higher than surrounding sediments.