Metagenomic analysis reveals soil microbiome responses to microplastics and ZnO nanoparticles in an agricultural soil

Both microplastics (MPs) and engineered nanoparticles are pervasive emerging contaminants that can produce combined toxicity to terrestrial ecosystems, yet their effects on soil microbiomes remain inadequately understood. Here, metagenomic analysis was employed to investigate the impacts of three common MPs [i.e., polyethylene (PE), polystyrene (PS), and polylactic acid (PLA)] and zinc oxide nanoparticles (nZnO) on soil microbiomes. Both MPs and nZnO significantly altered the taxonomic, genetic, and functional diversity of soil microbes, with distinct effects depending on dosage or type. Archaea, fungi, and viruses exhibited more pronounced responses compared to bacteria. Higher doses of MPs and nZnO reduced gene abundance for nutrient cycles like C degradation and N cycling, but enhanced CO fixation and S metabolism. nZnO consistently decreased the complexity, connectivity, and modularity of microbial networks; however, these negative effects could be mitigated by co-existing MPs, particularly at elevated doses. Notably, PLA (10 %, w/w) exhibited greater harm to fungal communities and increased negative interactions between microbes and nutrient-cycling genes, posing unique risks compared to PE and PS. These findings demonstrate that MPs and nZnO interact synergistically, complicating ecological predictions and emphasizing the need to consider pollutant interactions in ecological risk assessments, particularly for biodegradable MPs.