Impact of Polypropylene Microplastics on Earthworm Performance and Vermicompost Nutrient Characteristics on the Vermicompost Process of Cow Manure

The increasing presence of microplastics in organic fertilizers raises concerns regarding their potential impacts on vermicomposting processes and the quality of vermicompost products. This study aimed to evaluate the effects of polypropylene (PP) microplastics (MPs) on earthworm performance, vermicomposting dynamics, and vermicompost nutrient characteristics. The experiment was conducted using Eisenia fetida in a microcosm system with four treatments: control without microplastics (P0) and cattle manure amended with 1 g (P1), 2 g (P2), and 3 g (P3) of PP microplastics, each with three replicates. Vermicomposting was carried out for 14 days using 80 g of substrate per unit at 70% moisture content. The results showed that earthworm survival rates remained high across all treatments (84–92%), while body weight decreased at higher microplastic concentrations, with the lowest value observed at 3 g PP (58). Temperature (14.0–28.5°C) and pH (7.5–8.0) remained stable, whereas fertility exhibited strong fluctuations, reaching up to 3000 µS/cm in microplastic treatments, accompanied by increased C/N ratios from 20 (control) to 24 (3 g PP), indicating slower organic matter decomposition. In conclusion, polypropylene microplastics did not induce acute toxicity during vermicomposting but significantly altered sublethal biological responses and nutrient mineralization processes. These findings highlight potential risks of microplastic-contaminated vermicompost to agroecosystem sustainability and emphasize the need to incorporate microplastic considerations into organic waste management and fertilizer quality assessments.