Particle size-dependent developmental and neurotoxic effects of epoxiconazole nanoformulations and its active ingredient in zebrafish larvae.

Epoxiconazole (EPO), a widely used triazole fungicide that can enter aquatic ecosystems through agricultural runoff, poses potential risks to non-target aquatic organisms. Although nano-enabled pesticide formulations can control release and reduce application rates, their toxicological evaluation remains insufficient, particularly with respect to size-dependent biological effects. Here, zebrafish larvae were exposed to free EPO and EPO-loaded mesoporous silica nanoparticles (EPO@MSNs) with particle sizes of 30, 150 and 450 nm to investigate size-associated differences in developmental toxicity and their underlying mechanisms. Overall, EPO exposure induced developmental and neurovascular abnormalities, neurobehavioral impairment, and neurotransmitter imbalance, accompanied by oxidative stress, innate immune activation, inflammation, and apoptosis. Nanoencapsulation reshaped the toxicological profile of EPO, with the overall toxicity, as integrated by PCA, following the order EPO@MSNs-30 < EPO@MSNs-150 < EPO@MSNs-450 < free EPO. Transcriptomic analyses further demonstrated that nanoformulation shifted the dominant molecular responses from metabolism- and detoxification-related processes in free EPO toward nanoparticle-associated intracellular processing in EPO@MSNs-30 and broader extracellular matrix, vascular, and inflammatory responses in EPO@MSNs-450. These findings demonstrate that particle size is associated with both the overall toxicological profile and the molecular response patterns of MSN-based pesticide formulations, providing mechanistic insights for the biosafety assessment and rational design of nano-enabled pesticide formulations.