Systematic review of microplastic concentrations in water and fish: Modelling distribution patterns and transport dynamics across the Mediterranean Sea.

Microplastics (MPs) are pervasive marine contaminants, yet Mediterranean-scale assessments remain constrained by fragmented spatial coverage, inconsistent metrics, and limited integration between observations and transport processes. Here, we combine a harmonised systematic review of MP concentrations in surface waters and fish with basin-scale Lagrangian particle tracking to resolve distribution patterns, connectivity, and exposure pathways across Mediterranean Geographical Sub-Areas (GSAs). From 591 screened records (2012-2026), 108 empirical studies met strict inclusion criteria. Concentrations were standardised to items m-3 for surface waters and items individual-1 for fish, enabling direct GSA-level comparisons. The mean Mediterranean surface-water concentration was 2.12 ± 10.52 items m-3, with pronounced hotspots in the Levant, Sardinia West and Cyprus Island (GSAs 27, 11.1, and 25, respectively), and a maximum concentration of 324.10 items m-3 observed in the Levantine basin. MP ingestion was widespread across 90 species and three taxa identified at genus level, yet no clear spatial coupling was observed between water and fish contamination, indicating that biological exposure cannot be inferred from local surface concentrations alone. To interpret these patterns, we simulated MP transport using OpenDrift forced by Copernicus Marine reanalysis (2005-2020), releasing 579,960 particles tracked for four years. Simulations show net accumulation in southeastern basin GSAs, frequent coastal interaction (58.5% beaching/contact), and slightly stronger connectivity among water hotspots (33.4%) than between water and fish hotspots (21.2%). By integrating harmonised observations with process-based modelling, this study provides the first basin-scale assessment linking MP transport dynamics to biological exposure in the Mediterranean Sea.