Microplastic pollution characteristics in global marine sediments: A meta-analysis

Microplastics (MPs) pollution in marine environments has attracted widespread attention worldwide. Sediments are hotspots of MPs pollution. However, a comprehensive understanding of the distribution characteristics and driving factors of microplastics in coastal sediments is still lacking. The results revealed substantial variation in sediment MP abundance, with values ranging from 7.6 to 4213 particles/kg; the overall pooled abundance was 186.24 particles/kg (95% CI: 132.39-262.00), with substantial residual heterogeneity among the included estimates. Smaller MPs (<1 mm) accounted for over 60% of all detected MPs in global sediments. Transparent, fibrous and Polyethylene were the most common color, morphology and polymer type of MPs, respectively. Based on redundancy analysis (RDA), driving factors of MP morphological characteristics were explored. The results showed that flotation density and identification methods were the main sources of methodological bias in the observed MP characteristics. Significant differences in microplastic color distribution were observed among different countries. We divided the studies into four subgroups according to the distance from the coast. Although MP abundance exhibited certain spatial variations across regions, regional factors could explain only a small fraction of the observed heterogeneity. In contrast, the multivariable model explained 48.3% of the heterogeneity, highlighting the importance of methodological variability and the need for more standardized sampling and analytical procedures. This study identified small MPs and low-density polymers as key components of global sedimentary MP pollution and highlighted the need for standardized detection methods, supporting targeted monitoring of these MPs and harmonized protocols for global marine sediment assessment.