Assessment of microplastic contamination in compost leachate: insights from a municipal compost plant in Isfahan, Iran

The increasing production of waste has become one of the major environmental challenges of our time, particularly in waste management. While the composting process can transform municipal waste into a valuable product, the presence of plastics and microplastics (MPs) (< 5 mm) in the waste and their integration into the final compost and leachate pose significant environmental concerns. This is the first study to analyze the abundance of MP in the compost leachate from one of the Isfahan compost plant (S1), located in one of Iran's major cities with high population density, during the summer season. MPs were counted using a stereomicroscope, and fourier transform infrared spectroscopy (FTIR) was utilized to identify polymer types. The results revealed an average abundance of MPs in the S1 leachate during the summer of 992.66 ± 100.85 items/L. Over 62% of the MPs identified in this study fell within the 1000-5000 μm size range, with a concentration of 610.28 ± 59.26 items/L. Polystyrene and polyamide emerged as the most frequently identified polymers (18.46% and 16.8%), and fragments were the most commonly observed shape among the MPs. This study underscores that compost leachate contains high concentrations of MPs that can disseminate into various environmental compartments such as groundwater, surface water, soil, and even air. Consequently, compost leachate should be recognized as a significant source of MPs entering the environment.