Influence of phosphate on phytotoxicity of ceria nanoparticles in an agar medium

Fate and toxicity of manufactured nanoparticles (NPs) in the living organisms and the environment are highly related to their transformation. In the present study, the effect of phosphate on the phytotoxicity and transformation of CeO₂ NPs was investigated in an agar medium using head lettuce plants that are sensitive to Ce³⁺ ions. Plants were treated by CeO₂ NPs with or without phosphate for 10 days. Results suggest that the treatments of P deficiency (P(-)) and CeO₂ NPs (P(+)&Ce) could separately induce significant inhibition on the growth of lettuce seedlings and cause oxidative stress, but the inhibition was the most serious when the two conditions were combined (P(-)&Ce). In the absence of phosphate, more CeO₂ NPs were transformed to Ce(III) in the roots and more Ce³⁺ ions were translocated to the shoots, which induced higher toxicity to head lettuce. Phosphates could alleviate the phytotoxic effect of CeO₂ NPs through the precipitation of dissociated Ce³⁺ ions. Considering the wide existence of phosphate in the environment, phosphate-related transformation may be a critical factor in evaluating the toxicity and fate of many other metal-based NPs.