Characterization and risk assessment of microplastics in shoreline sediments of the Yellow River Delta

As the intersection of river, sea, and land, river deltas are hotspots for the accumulation of microplastics (MPs). This study investigated the abundance and characteristics of MPs in surface sediments from shoreline area of the Yellow River Delta in northern China, elucidated their sources, and assessed their risk. The MPs isolated from sediment samples were detected and characterized using optical microscopy and micro-Fourier transform infrared spectroscopy (μ-FTIR). The results showed that MPs were abundant (360-2160 items/kg) in the area, and occurred mainly in small sizes (<250 μm), as fibers (20.2-50.0%), filament (4.8-21.5%), and granules (8.5-20.6%), and in transparent (27.8-40.3%), blue (11.2-31.6%), or black (7.9-26.5%) color. Polyethylene terephthalate (26.08%), polyethylene (20.47%), polypropylene (13.49%), and polyvinyl chloride (10.71%) were the dominant polymer types for the MPs. The pollution load indices (1-6) indicated that all sampling sites were polluted by MPs, while the polymeric hazard indices (65.14-91.44) suggested that MPs pollution of the area was in medium range. Overall, the ecological risk indices (91.44-475.38) of the sampling sites indicated that MPs in shoreline sediments of the Yellow River Delta posed low to considerable potential ecological risk. While the dominance of polymers with medium polymeric risk scores rendered the MPs in the shoreline sediments with relatively low risk, the majority of MPs occurred in small sizes, which complicates the actual risk posed by MPs in shoreline sediments of the Yellow River Delta and deserves attention.