Use of CeO2, TiO2 and Fe3O4 nanoparticles for the removal of lead from water: Toxicity of nanoparticles and derived compounds

Nanoparticles (NPs) suspensions of CeO2, Fe3O4 and TiO2 were synthesized and tested for lead removal in water cleaning processes. The results obtained are promising for the use of these NPs in lead elimination via adsorption process. The adsorption capacity obtained for the NPs was: 189 mg Pb/g NPs CeO2, 83 mg Pb/g NPs Fe3O4 and 159 mg Pb/g NPs TiO2. Another important issue assessed in this study was to determine the toxicity of the NPs in each step of the process: synthesized NPs, NPs after lead adsorption and the supernatant after NPs separation. In order to study the interaction with living organisms and prevent future environmental damages, the Germination test in Tomato (Lycopersicom esculentum), Lettuce (Lactuca sativa), Cucumber (Cucumis sativus) seeds and the Microtox® assay, based on the use of bioluminescent marine bacterium, Photobacterium phosphoreum/Vibrio fischeri, were used to evaluate the toxicity of these materials. The CeO2 NPs showed a high level of lead removal although presented a high phytotoxicity. The TiO2 NPs inhibited the lead toxicity against the marine bacterium. Interestingly, the media used to stabilize the NPs (tetramethylammonium hydroxide and hexamethylenetetramine) presented a significant reduction in the germination index. TiO2 and Fe3O4 NPs did not exhibit any toxicity and could be used as absorbents for Pb (II) removal.

Research Highlights
► Experiments have shown the elimination of lead using several types of nanoparticles.
► Adsorption is the main process involved in lead removal by nanoparticles.
► Standard toxicity tests have shown the toxicity of the several species involved in adsorption.
► Cerium oxide nanoparticles showed a high level of lead removal although presented high phytotoxicity.
► Titanium oxide nanoparticles inhibited the lead toxicity in the Microtox test.