Size-dependent toxicological effects and mechanisms of PET microplastics in Pacific white shrimp (Penaeus vannamei).

Microplastics (MPs) have emerged as critical contaminants of global concern, yet the size-dependent toxicity of MPs remains underexplored, particularly in aquaculture and food source species. This study aimed to evaluate the physiological, behavioral, histological, and transcriptomic impacts by polyethylene terephthalate (PET) MPs of different size classes: small (PETS; 9.09 μm), medium (PET-M; 49.00 μm), and large (PET-L; 158.59 μm) on Penaeus vannamei (Pacific white shrimp), a commercially important species. Shrimp were exposed to MPs for 21 days, and multiple endpoints were assessed, including growth rate, swimming ability, and histological features (hepatopancreas and intestinal ultrastructure). Additionally, transcriptomic analysis using RNA-seq revealed key mechanisms involved in oxidative stress, inflammatory activation, metabolic and nutrient transport following PET-MP exposure. The smaller-sized MPs (PET-S and PET-M) caused reductions in growth and motility in Pacific white shrimp, along with pronounced tissue damage. In contrast, the PET-L group exhibited a partial recovery in growth, accompanied by compensatory physiological and molecular responses. These findings indicate the importance of particle size on the severity and effects of MP fragments that smaller MPs pose a greater risk to shrimp health and aquaculture productivity, thereby providing valuable insights for refined ecological risk assessments and ensuring food safety management in aquatic environment. ENVIRONMENTAL IMPLICATIONS: Microplastic pollution in marine environments poses a direct threat to shrimp, a key food source and ecological species. This study reveals that PET microplastics, especially smaller particles, cause severe physiological and molecular damage to Pacific white shrimp (Penaeus vannamei), impairing growth, mobility, and organ integrity. Larger particles induced partial adaptive responses, but overall health risks remained. These findings provide urgent evidence that microplastic size critically affects toxicity, highlighting serious implications for ecosystem stability, seafood safety, and human health.