Size-induced toxic effect of plastic particles on earthworms characterized by gut multi-omics analysis

The emission and accumulation of plastic particles in soil have raised concerns about their impact on soil organisms. As key components of soil fauna, earthworms (Eisenia fetida) are prone to ingesting plastic particles and experiencing associated health effects. However, the size-dependent toxicological mechanisms of these particles in earthworms remain unclear. In this study, earthworms were exposed to polystyrene particles of different sizes (50 nm, 200 nm, and 250 μm), and their biological responses were evaluated through morphological analysis, gut microbiota profiling, and metabolomics. Micro-sized particles (250 μm, 200 mg kg^-1) caused mechanical damage to intestinal tissues and reduced survival rates after 28 days. Nano-sized particles (50 nm, 200 nm) disrupted gut microbial diversity and altered metabolic profiles, including reductions in amino acids involved in the TCA cycle. All particle sizes affected metabolite levels and key metabolic pathways. These results indicate that micro-sized particles primarily induce acute physical damage, while nano-sized particles exert long-term biochemical effects. This study highlights the size-specific ecological impacts of plastic particles on soil invertebrates.