Fate and behavior of iron oxide nanoparticles in the environment : impacts on trace metal mobility and soil-plant systems
Engineered Iron Oxide Nanoparticles (IONPs) are specific nanoscale materials that have recently been used into wide environmental applications. The dispersion of IONPs into soils and waters, as well as their interactions with living organisms, raise many scientific issues. The first part of this work is intended to provide a thorough characterization of IONPs in aqueous solution, from their intrinsic physico-chemical properties to their colloidal behavior and chemical reactivity. Surface modifications are applied to evidence the key role of surface chemistry towards most interactions IONPs encounter. In particular,humic acid reduce NPs-Fe aggregation and display a high adsorption capacity for trace metals, especially copper (Cu). On the other hand, the pH of the solution play a critical role towards NPs-Fe interactions. Depending on the pH, the surface charge of the particles are modifiedand hence pH is involved in the electrostatic forces that drive the particles aggregation state and contribute to metal adsorption. The last part of the study is focused on the interactions occurring with IONPs in presence of plants. Several experiments are conducted in aqueous solution and in soil columns to precise the impacts of IONPs on the growth medium and to assess the effects of IONPs on plants. Results (magnetic susceptibility) show that IONPs manage to penetrate the roots of beans and sunflower plants (57 and 63 days-old) and that they are translocated to the aerial parts in low amounts. Plants respond to IONPs penetration by increasing the plant biomass and the chlorophyll contents and by decreasing the lipid peroxidation.
Key words : iron oxide nanoparticles, oxidation, aggregation, adsorption, element trace metals, plants.