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Abundance and Characterization of MPs in Composts Produced in Mazandaran, Iran
Summary
A cross-sectional study of three compost factories in Mazandaran, Iran found a mean microplastic concentration of 16,981 items per kilogram, with fibers comprising 75% of particles and polyurethane, polyamide, and LDPE among the identified polymers. Compost derived from municipal solid waste is a significant and underappreciated vehicle for introducing microplastics into agricultural soils, contaminating land that grows food for human consumption.
Plastic waste from various sources contributes significantly to environmental and food chain contamination through microplastics (MPs). MPs are defined as plastic particles with dimensions smaller than 5 mm. The short lifespan of plastic packaging materials leads to their rapid accumulation in municipal solid waste. Composting processes face challenges in completely separating plastics, resulting in MP contamination of compost products. This cross-sectional study investigates the prevalence, distribution, and characteristics of MPs in compost produced by three compost factories in Mazandaran province, north of Iran. MP extraction from compost samples was performed using density separation and digestion techniques. Stereomicroscopic analysis was employed for MP characterization. The results revealed a mean MP concentration of 16,981 items/kg across all compost samples. Behshahr compost exhibited the highest average concentration at 18,622 items/kg, while Babol had the lowest at 15,744 items/kg. Kruskal–Wallis analysis indicated no statistically significant differences among sampling stations (p > 0.05). Fibers were the predominant shape (75%), with transparent-white being the most common color (56%). The size range of 500–1000 µm accounted for 40% of observed MPs. Polymer analysis identified the presence of polyurethane (PU), polyamide (PA), low-density polypropylene (LDPE), and polycarbonate (PC). The study demonstrates the ubiquity of MPs in compost from Mazandaran’s compost facilities. To mitigate this issue, strategies for reducing plastic waste input into composting facilities and implementing effective monitoring programs for MP hotspot detection and identification are imperative.