Effects of surface modification on toxicity of CeO₂ nanoparticles to lettuce

Phytotoxicity of nanoceria (nCeO₂) has been reported, but there are few studies on how to reduce its phytotoxicity. In the present study, we modified nCeO₂ with two organophosphates (nCeO₂@ATMP and nCeO₂@EDTMP) and compared their toxicity to lettuce with that of uncoated nCeO₂. The results showed that bare nCeO₂ significantly inhibited the root growth of lettuce, leading to oxidative damages and root cell death. In contrast, after surface modification, the toxicity of nCeO₂@ATMP to lettuce was weakened, while nCeO₂@EDTMP was nontoxic to lettuce. It was found that the surface properties of the modified materials have been changed, resulting in sharp decreases in their bioavailability. Although nCeO₂ with and without surface coatings were all transformed when interacting with plants, the absolute contents of Ce(III) in roots treated with modified nCeO₂ decreased significantly, which may be the main reason for the reduction of toxicity. This study indicates that it is feasible to reduce the phytotoxicity of nanomaterials through surface coating.