Microplastics as emerging contaminants in municipal solid waste compost: Distribution, characterization, and ecological risk

The increasing abundance of microplastics (MPs) in water and soil has raised significant environmental concerns. This study evaluated the abundance and ecological risks of MPs in compost produced from three composting facilities (S1-S3) in Isfahan province, central Iran. Monthly samples were collected over a year, and MPs were extracted using an adapted protocol involving organic matter digestion with 0.05 M Fe (II) solution and hydrogen peroxide (H2O2), followed by density separation using saturated zinc chloride (ZnCl2). Despite rigorous methods, limitations remain due to the lack of a global standard and inherent errors in existing MP extraction protocols. The extracted MPs were analyzed under a stereomicroscope, and polymer types were identified via Micro-Raman spectroscopy. Ecological risks were assessed using established indices, including the Polymer Hazard Index (PHI), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI). The results revealed that the average MPs abundance in S1, S2, and S3 were 44,267 +/- 7,240, 38,500 +/- 6,130, and 34,267 +/- 5297 items/kg dry compost, respectively. MPs larger than 1000 mu m accounted for 41 %-49 % of the total, with fragments being the most prevalent shape (49 %-51 %). Polyethylene terephthalate, polyethylene, and polyolefin were the dominant polymers in all facilities. The ecological risk indices indicated high levels of risk in all three composting sites, with potential implications for agricultural soils, soil fertility. MPs in compost may enter the food chain, raising concerns for ecosystem health. These findings underscore the significant MP contamination in compost and highlight the need for improved solid waste management strategies to reduce plastic pollution.