Abstract:Microplastics (MPs), as emerging contaminants, have become a prominent research focus within global environmental science. The Yellow River Estuary, a nationally significant estuarine wetland and ecological conservation zone in China, represents a critical area for investigating MP pollution in intertidal environments. Studying the contamination characteristics of MPs in this region not only advances understanding of terrestrial MP transport processes to the marine environment but also provides a scientific basis for ecological risk assessments of MPs in estuarine systems. This study systematically analysed the distribution patterns, morphological characteristics, and sources of MPs (53–5000 μm) within surface sediment samples collected from intertidal zones both within and outside the Yellow River Delta, whilst also assessing their ecological risks. Results demonstrate distinct spatial variations in MP abundance: the inner delta exhibited a decreasing gradient from east to west (range: 60–520 items/kg; mean: 257.5 ± 166.58 items/kg), while the outer delta displayed an inverse pattern (range: 160–880 items/kg; mean: 360 ± 249.8 items/kg). This distribution pattern is primarily governed by the dispersion of Yellow River freshwater plumes under the influence of the counterclockwise circulation in the southern Bohai Sea. Morphological analysis revealed fibrous MPs as the predominant type (54.7% in outer delta; 35.8% in inner delta), followed by granular fragments (17.2% in outer delta; 25.9% in inner delta), with small-sized MPs (<1 mm) dominating both regions (57.5% in outer delta; 74% in inner delta). Polymer composition showed regional differentiation: the outer delta was dominated by cellulose (43.7%) and polyethylene terephthalate (18.8%), primarily derived from domestic wastewater, while the inner delta exhibited comparable proportions of cellulose (23.5%), polyethylene terephthalate (23.5%), and polyvinyl chloride (23.5%), indicating predominant input of industrial-source secondary MPs via fluvial transport. Pollution Load Index (PLI) assessment indicated overall mild contamination levels (PLI<1) across the study area, with higher contamination in the inner delta (PLI=0.765) compared to the outer delta (PLI=0.629). Specific stations B5 and B6-2 reached moderate pollution levels. These findings provide significant implications for ecological conservation strategies in the Yellow River Delta.
