Transfer and transformation of CeO2 NPs along a terrestrial trophic food chain†
CeO2 NPs could be inevitably exposed to terrestrial organisms and food chains with their agricultural applications. The transfer and transformation of CeO2 NPs were therefore investigated within a tri-trophic terrestrial food chain, i.e., lettuce–hornworm–chicken. The results showed that CeO2 NPs were accumulated by lettuce (Lactuca sativa L.) roots and translocated to leaves in a dose-dependent manner after exposure to CeO2 NPs (2–1000 mg L−1) for 10 days via roots. The obtained CeO2 NP-containing leaves (14.37, 35.71 mg Ce per kg dry weight) were fed to hornworms (Spodoptera litura F.). The Ce contents in hornworms were 6.78 and 8.78 mg per kg dry weight, respectively, and the majority of Ce (13.51 and 26.03 mg per kg dry weight, respectively) was excreted to feces. In the case of chickens (Gallus gallus domesticus), Ce was mainly distributed in their intestines and stomachs from leaf and hornworm dietaries. Biomagnification factors of CeO2 NPs were 0.179, 0.246 and 0.403 after the transfers through lettuce–chicken, lettuce–hornworm, and hornworm–chicken, respectively, suggesting that no biomagnification occurred during both bi- and tri-trophic food chain exposures. As detected by X-ray absorption near edge structure, Ce primarily remained as CeO2 in the lettuce roots (83.4%) and leaves (72.4%) after root exposure, Ce(III)-cysteine (52.1%) in the hornworms under trophic exposure, and CeO2 in the intestines (85.1 and 87.1%, respectively) of chickens after leaf and hornworm dietaries. These results indicated that the transfer and transformation of CeO2 NPs are independent of the number of trophic levels. This research provides further insight into the fate of NPs in terrestrial ecosystems and their possible risks to food safety.