Microplastics Contamination and Ecological Risk Assessment in Natural and Afforested Mangrove Stands of Bahrain: Abundance, Polymer Composition, and Onshore-Offshore Variability.

Mangrove ecosystems are ecologically important coastal habitats, yet data on microplastic (MP) contamination along Bahrain's coasts remain scarce. This study investigated the abundance, characteristics, and ecological risks of MPs in sediments from four mangrove sites (12 stations) collected in 2025. MPs were extracted via density separation and characterized by size, shape, color, and polymer composition using Raman spectroscopy; ecological risk was assessed using the Pollution Load Index, Polymer Hazard Index, and Potential Ecological Risk Index. MPs were detected at all stations, with abundances ranging from 533.33 ± 2.08 to 958.33 ± 6.5 particles/kg dry weight. Fragments were dominant in shape, and black was the dominant color. Particles < 10 μm and 10-30 μm were the most abundant size classes, with the sub-10 μm fraction, uncharacterized in Gulf mangrove ecosystems, suggesting that current methods underestimate MP abundance and associated ecological risk. Given their high surface reactivity, adsorption capacity, and potential root uptake, these ultrafine particles highlight the need for standardized, high resolution detection methods. Nylon-6 predominated all sampling sites, irrespective of their onshore or offshore setting, indicating common and persistent anthropogenic sources. Although ecological risk indices suggested an overall low-to-moderate environmental risk, the ubiquitous occurrence of MPs throughout Bahrain's mangrove sediments raises concern regarding their long-term ecological implication. These findings provide a robust baseline for future spatiotemporal monitoring, refined ecological risk assessments, and the formation of targeted management strategies to safeguard coastal ecosystems.