Tracing The Fate of Microplastics in a Wastewater Pond System: Abundance, Characteristics, and Environmental Risk Assessment

Document Type : Original Research Paper

Authors

1 Department of Natural Ecosystems Management, Hamoun International Wetland Institute, Research Institute of Zabol, Zabol, Iran

2 Department of Aquatic Sciences, Hamoun International Wetland Institute, Research Institute of Zabol, Zabol, Iran

10.22059/poll.2026.407330.3217

Abstract

Microplastics (MPs) have emerged as a critical environmental pollutant due to their persistence, mobility, and potential toxicity. This study assessed the abundance, characteristics, polymer composition, and removal efficiency of MPs in the Zabol municipal wastewater treatment plant, which operates via a stabilization pond system. Influent and effluent samples were collected during the winter of 2024 and summer of 2025 and analyzed for size, morphology, color, and polymer type using stereomicroscopy and Fourier transform infrared (FTIR) spectroscopy. The abundance of the MPs ranged from 17.53 ± 0.64 MPs/L (1 mm, winter) to 962.7 ± 12.86 MPs/L (45–425 µm, summer) in the influent and from 5.86 ± 0.25 MPs/L (1 mm, summer) to 26.24 ± 2.09 MPs/L (1 mm, winter) in the effluent. Film-shaped MPs dominated in both seasons, representing 54%–61% of the influent and 51%–65% of the effluent particles, while golden and transparent colors prevailed. FTIR analysis identified polyethylene (PE) and polypropylene (PP) as the major polymers, followed by polyamide (PA), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (PS). The overall removal efficiencies were 95.57% in winter and 97.48% in summer. Although the polymer hazard index (PHI) and pollution load index (PLI) significantly decreased after treatment (P < 0.05), the effluent samples still exhibited a moderate hazard (Level II) due to the presence of persistent dense polymers such as PVC, PS, and PU. These findings indicate that while stabilization ponds achieve substantial MP removal, fine and buoyant particles—particularly PE and PP—can escape into the environment, emphasizing the need for advanced tertiary treatment and improved source control strategies in arid regions.

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