ارزیابی ریسک اکولوژیک میکروپلاستیک‌ها در تصفیه‌خانه فاضلاب شهری با تأکید بر تغییرات فصلی

Introduction: Microplastics are considered emerging environmental pollutants that pose a serious threat to ecosystems due to their high persistence and ability to transport toxic contaminants. Wastewater treatment plants are among the major pathways through which these particles enter environments. This study aimed to investigate the abundance, polymer composition, removal efficiency, and ecological risk of microplastics in a wastewater treatment plant with emphasis on seasonal variations.
Methods: The study was conducted at a municipal wastewater treatment plant (13,000 m³/day). Twenty-four-hour composite influent and effluent samples were collected during winter and spring. After organic matter digestion and density separation, microplastics were identified by stereomicroscopy, FTIR, and micro-Raman spectroscopy. The Pollution Load Index (PLI) and Potential Ecological Risk Index (H) were also calculated.
Results: The mean concentrations of microplastics in influent wastewater during winter and spring were 3158±214 and 7532±429 particles/m³, respectively, while the corresponding effluent concentrations were 463±162 and 926±245 particles/m³. Removal efficiencies were 85.3% in winter and 87.7% in spring. Polypropylene (41.72%) and polyethylene (29.43%) were the dominant polymers. The ecological risk index was calculated as 1455.79, indicating a high ecological risk. Furthermore, PLI values of 6.82 and 8.13 reflected severe pollution conditions.
Conclusion: Although the wastewater treatment plant demonstrated high efficiency in removing microplastics, the considerable levels of these pollutants in the treated effluent and the elevated ecological risk indicate a continued threat to receiving aquatic environments. The findings highlight the necessity of upgrading treatment technologies, implementing advanced microplastic removal processes, and adopting source-control management strategies to mitigate environmental impacts.