Microplastic Contamination in Mangrove Sediments: A Systematic Review of Abundance, Composition, and Environmental Drivers[

Graphical Abstract Highlight Research 1. Mangrove sediments function as global sinks for microplastics, with accumulation is shaped by the interaction between anthropogenic inputs and natural retention mechanisms, particularly mangrove root density, tidal hydrodynamics, and fine-grained sediments. 2. Fibers and fragments dominated the recovered particles, with polyethylene (PE) and polypropylene (PP) consistently identified as the predominant polymers. 3. Urbanization, wastewater discharge, riverine transport, tourism, fishing, and aquaculture are major pathways contributing to microplastic accumulation in mangrove sediments. 4. Methodological heterogeneity, particularly density separation media, particle-size thresholds, and visual identification, substantially limits cross-study comparability. 5. International standardization of sampling, high-density flotation, contamination controls, and spectroscopic polymer confirmation is essential for reliable global monitoring of mangrove microplastics. Abstract Mangrove ecosystems are critical sinks for marine microplastics because their complex root systems, low-energy hydrodynamics, and fine-grained sediments promote particle retention. However, global assessments remain fragmented due to spatially variable environmental drivers and methodological heterogeneity. This systematic literature review aimed to synthesizes global patterns of microplastic abundance and composition in mangrove sediments, identifies natural and anthropogenic drivers of accumulation, and evaluates methodological effects on data comparability. This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 framework which conducted in July 17th, 2026. Literature searches conducted in the Scopus database identified 97 records. After screening, full-text eligibility assessment, and quality appraisal, 37 empirical studies were retained for qualitative synthesis and subsequent analysis. Empirical studies were systematically reviewed and compared based on geographical distribution, microplastic abundance and characteristics, environmental and anthropogenic drivers, and analytical methods, including sampling, density separation, particle identification, and polymer verification. Microplastic abundance ranged from 12 to >6,000 particles kg⁻¹ dry sediment, with substantial spatial heterogeneity. Studies were concentrated in tropical Asia and Brazil. Fibers and fragments predominated, while polyethylene and polypropylene were the dominant polymers. Root density, tidal hydrodynamics, and fine sediments influenced retention, whereas urbanization, wastewater, and maritime activities represented major inputs. Density separation using NaCl versus ZnCl₂ and visual identification without spectroscopic confirmation affected reported abundances. Standardized sampling, high-density flotation, contamination controls, and spectroscopic verification are needed to improve comparability. Future research should expand geographical coverage and adopt standardized protocols to strengthen global monitoring of microplastics in mangrove blue-carbon ecosystems.