Influence of Polyethylene Terephthalate and Polystyrene Microplastics on Microbial Dynamics in Rice Straw Composting

Microplastics have emerged as critical pollutants in terrestrial ecosystems, yet their effects on composting processes remain poorly characterized. This study investigated the influence of polyethylene terephthalate (PET) and polystyrene (PS) microplastics on rice straw composting using controlled experiments with 0.5% (dry weight) PET and PS additions. Microbial community dynamics were assessed through 16S rRNA metagenomic sequencing and flow cytometry with principal component analysis (PCA), while compost quality was evaluated by monitoring temperature, electrical conductivity, pH, nitrate and phosphate levels, humic acid content, organic matter humification, and seed germination index. PET and PS significantly disrupted composting performance, reducing microbial diversity and promoting stress-tolerant genera such as Bacillus, Pseudomonas, and Halomonas. Nitrate levels were 1.25-fold and 1.33-fold lower in PET and PS treatments compared to CK, humic acid content declined, and germination indices dropped to 37.25% and 32.26% versus 78.68% in CK. PCA revealed slower humification and reduced nitrogen cycling, while SEM and FTIR confirmed the persistence of PET and PS microplastics after composting. These findings highlight the adverse impacts of microplastics on compost quality and microbial processes, underscoring the need for strategies such as source reduction, the use of biodegradable alternatives, and the optimization of composting technologies to minimize microplastic contamination and protect soil health and agricultural sustainability. Microplastics decreased microbial diversity by 12%, lowering the Chao1 index. Microplastics reduced compost maturity, nitrate by 20%, and GI by 50%. PET and PS resisted degradation, remaining chemically intact over 90 days. Core microbes show 30% reduced functionality with microplastics present. PET and PS treatments disrupted archaeal community balance.