Biomagnification in Trophic Transfer: Mechanisms of Trans-Trophic Toxicity from Co-Contamination of Aged NPs and TBP in a Soil–Rye–Armyworm System

The co-contamination of nanoplastics and organic pollutants poses a potential threat to agricultural ecosystems and food chain safety. To systematically reveal the individual and combined toxicity of aged carboxylated nanoplastics (NPs-COOH) and the flame retardant tributyl phosphate (TBP), as well as their transmission mechanisms along the food chain, this study established a "rye-armyworm" model. A multiscale investigation was conducted by integrating molecular docking, multiomics, and traditional toxicological methods. Results indicated that NPs-COOH and TBP form complexes via electrostatic and van der Waals interactions, synergistically enhancing their accumulation in rye roots and translocation into the vascular system. Combined exposure exerted synergistic toxicity on rye, manifested as inhibited photosynthesis, exacerbated oxidative stress, and significant deterioration in yield and nutritional quality. Transcriptomic and microbiome analyses further revealed that rye responds to the stress by systemically activating stress-response and detoxification metabolic pathways, accompanied by disruption of beneficial rhizospheric microbial communities. The pollutants were transferred along the food chain, with TBP undergoing biomagnification from rye to armyworm (BMF = 1.57), leading to growth inhibition, midgut structural damage, suppression of key detoxifying enzyme activities, and gut microbiota dysbiosis. This study elucidates the multidimensional ecological risks arising from the "vector effect" and synergistic toxicity of NPs-COOH and TBP in the soil-plant-insect system, providing further insights for a comprehensive assessment of the threats posed by such co-contamination to agricultural product safety and food chain health.