Trophic Transfer and Transformation of CeO₂ Nanoparticles along a Terrestrial Food Chain: Influence of Exposure Routes

The trophic transfer and transformation of CeO 2 nanoparticles (NPs) through a simulated terrestrial food chain were investigated using a radiotracer technique and X-ray absorption near edge structure (XANES). Radioactive 141 CeO 2 NPs were applied to head lettuce ( Lactuca sativa ), treated via root exposure in its potting soil (5.5 or 11 mg/plant) for 30 days or foliar exposure (7.2 mg/plant, with half of the leaves treated and the other half not) for 7 days. Subsequently, two groups of land snails ( Achatina fulica ) were exposed to 141 Ce via either a direct (i.e., feeding on the lettuce leaves with 141 Ce-contaminated surfaces) or an indirect/trophic (i.e., feeding on the lettuce leaves with systemically distributed 141 Ce) route. To evaluate the influence of exposure routes, the Ce contents of the lettuce, snail tissues, and feces were determined by radioactivity measurements. The results show that both assimilation efficiencies (AEs) and food ingestion rates of Ce are greater for the trophic (indirect) exposure. The low AEs indicate that the CeO 2 NPs ingested by snails were mostly excreted subsequently, and those that remained in the body were mainly concentrated in the digestive gland. XANES analysis shows that >85% of Ce was reduced to Ce(III) in the digestive gland under direct exposure, whereas Ce in the rest of the food chain (including feces) was largely in its original oxidized (IV) state. This study suggests that CeO 2 NPs present in the environment may be taken up by producers and transferred to consumers along food chains and trophic transfer may affect food safety.