Silent contaminants in a vanishing wetland: microplastics and their ecological risks in the Gavkhoni Wetland sediments

Microplastics (MPs), as emerging organic pollutants, pose significant threats to ecosystems. This study investigated the presence and ecological risks of MPs in the sediments of the Gavkhoni Wetland, a recently desiccated yet ecologically important terminal basin of the Zayandeh-Rud River in central Iran. Fifty sediment samples were collected across three hydrologically distinct zones. An optimized extraction protocol using 0.05 M Fe(II) and HO digestion followed by ZnCl-based density separation was applied. MPs were quantified via stereomicroscopy and characterized using Micro-Raman spectroscopy. Three indices, Polymer Hazard Index (PHI), Pollution Load Index (PLI), and Pollution Risk Index (PRI), were employed to assess ecological risk. MP concentrations averaged 43,562.5 ± 9293.2, 21,187.5 ± 5806.9, and 9522.2 ± 3163.9 items/kg in Zones 1-3, respectively, with an overall mean of 24,148 ± 15,644.6 items/kg. Fragments were predominant, and 100-500 µm particles were most common. Polyethylene, polypropylene, and polystyrene were the dominant polymers. PHI, PLI, and PRI values categorized the site under 'Considerable,' 'Polluted,' and 'Dangerous' ecological risk levels, respectively. These results highlight severe MP contamination in a vulnerable dryland ecosystem and underscore the urgent need for targeted environmental management to address this emerging threat in arid and semi-arid wetlands.