Microplastic pollution in playas—endorheic basins with closed drainage systems. A study in surface sediments of Bakhtegan–Tashk Lakes (South Iran)

Microplastic contamination has become a growing environmental concern, yet its sources, distribution patterns, and ecological impacts remain largely unexplored in endorheic basins-ecosystems particularly vulnerable to contamination. This study investigates the abundance, composition, and spatial distribution of MPs in surface sediments (top ∼5 cm) of the desiccated Bakhtegan-Tashk Lakes, a saline playa spanning approximately 1260 km in southern Iran. Sediment samples collected from 26 shoreline sites revealed a mean microplastic concentration of 38.6 ± 19 particles (≥100 μm) per kilogram of dry sediment (kg d.w.). Fibres were the predominant microplastic, with black and navy blue being among the most frequently observed colours. Most particles exceeded 1 mm in size, although the smallest detected size was 100 μm. Raman spectroscopy identified nylon (polyamide) as the dominant polymer, constituting 39 % of the total MPs. The highest concentrations were recorded near the inflow of the Kor River into Bakhtegan Lake, a site impacted by municipal, industrial, and agricultural discharges. Sediment samples collected near roadways exhibited elevated microplastic levels compared to those from more remote locations. These findings suggest that riverine inputs and aeolian atmospheric deposition from roadways are significant contributors to MP contamination in this region.