Toxicity of metal oxide (CeO2, Fe3O4, SnO2) engineered nanoparticles on soil microbial biomass and their distribution in soil.

Aims of this work were to understand the effects of metal oxide (CeO2, Fe3O4, SnO2) engineered nano-particles (NPs) on microbial biomass and to evaluate their availability and distribution among soil particles. Two organ-mineral horizons (A1 and A2) of Epileptic Cambisol were polluted with NPs at rates of 0, 10 and 100 mg kg-1 of dry soil of Ce, Fe and Sn and incubated for 7 and 60 days at 60% WHC and at 25 °C. Both microbial biomass C and N were not statistically affected by NPs pollution whereas the microbial C/N ratio increased with Fe3O4 and SnO2-NPs probably due to the predominance of microbial communities such as ectomycorrhizae. The metabolic quotient (qCO2) significantly (P < 0.001) increased in polluted soils indicating microbial stress or changes in the bacterial/fungal biomass ratio. The CHCl3- labile amounts of free Ce and Fe were found in soil polluted with CeO2 and Fe3O4, indicating these elements were taken up by soil microorganisms. The chemical methods used for NPs bioavailability were not adequately sensitive to evaluate availability of elements in nanoparticles, and the best evaluation was from the water-soil partition coefficient (log Kd) showing a low solubility of NPs. Nanoparticles were found in soil small aggregates (2-53 and <2 µm) by infrared spectrometry (FTIR) and electron microscopy (ESEM-EDS). The study of interactions between NPs and both organic or inorganic compounds can give insights about the potential risks of NPs in soil. Furthermore the study on diversity of microbial communities will clarify the NPs toxicity on soil microbial communities.