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Microplastic Pollution in Compost Derived from Mixed Municipal Waste in Kermanshah City: Abundance, Characteristics, and Ecological Risk Evaluation
Summary
Researchers found that compost made from mixed municipal solid waste in Kermanshah, Iran, was universally contaminated with microplastics at an average of 2,160 particles per kilogram — translating to an estimated 118 million microplastics added to each hectare of farmland annually — posing medium to high ecological risk and highlighting compost as a significant pathway for microplastic entry into agricultural soils.
The breakdown and disintegration of plastic waste is one of the main ways that microplastics (MPs) enter the environment. Therefore, by collecting compost samples from the main compost production site in Kermanshah city, this study examined the presence of MPs in the compost obtained from mixed municipal solid waste (MSW). Sample preparation steps included hydrogen peroxide (H2O2) digestion, sodium iodide (NaI) flotation and filtration using a Buchner funnel flask and a glass fiber filter. Then the filters were analyzed using a stereomicroscope, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results showed that all compost samples were contaminated with MPs with an abundance range of 1000–4300 MPs/kg and an average of 2160 ± 968 MPs/kg. It was found that the use of compost from mixed MSW can add 118.8 × 106 MPs/ha to the soil annually. In terms of shape, the most frequency was related to fiber (75%) particles. Transparent/ white (56%), golden-brown (13%), and blue (13%) MPs had a greater share than other colors, respectively. Also, the most prevalent particles were those with a diameter of less than 2500 µm. MPs' surface morphological features indicated the existence of other contaminants and impurities. FTIR analysis identified the presence of polyethylene (PE) and polystyrene (PS) polymers in the compost samples. Based on the composition of the MPs in the compost, the study assessed three ecological risk scenarios and found a medium (H = 20.5) to high (H = 644) ecological risk associated with the presence of MPs. The study's conclusions highlight the need for practical methods to lessen MPs contamination in compost and other environmental systems. In order to reduce MPs pollution, this study also highlights how important it is to regulate the entry of plastic products into the consumption cycle and enhance waste management procedures. • The compost samples contained 1000 to 4300 MPs per kilogram. • Pollutants were present on the surface of MPs in the compost samples. • Fiber particles were the most frequent shape at 75%. • The presence of MPs in the compost posed a medium to high ecological risk. • All compost samples were contaminated with an average of 2160 MPs per kilogram.