Combined effect of nanoparticles and trace metals in a soil-plant-microbe ecosystem

Recent interest in the environmental fate and effects of manufactured CeO2 nanomaterials (NMs) has stemmed from its expanded use for a variety of applications including fuel additives, catalytic converters, mechanical planarization media, coating and other uses. The majority of these NMs will end up in wastewater treatment plants (WWTP) where they will partition to sewage sludge during wastewater treatment, and ultimately re-enter the environment through the application of biosolids to agricultural soils. Thus, soil may serve as a primary sink for NMs accumulation in the environment, in which NMs may enter food webs or cause direct toxicity to plants, microbial communities, or other soil organisms. This project aims to study (i) the impact of CeO2 NMs biotransformation on a soil-plant-microbe system using realistic exposure modes and (ii) the interaction between NMs and trace elements such as Cd, Pb, Zn, Ni, which are present both in the biosolid and in the soil. Pristine CeO2 NMs were first aged in a laboratory-scale activated sludge reactor during 5 weeks. The biosolid enriched NMs was then amended to an agricultural soil at environmentally relevant concentration: 1 mg.kg-1 CeO2. The soil is a sandy loam soil rich in Cd and Ni due to a long-term sewage sludge field experiment (INRA Couhin's experimental station, Bordeaux). Four treatments were performed: control soil, soil amended with 1 mg.kg-1 pristine CeO2 NMs, control biosolid without NMs, biosolid enriched NMs. The selected plant was canola (Brassica napus), an oil-producing plant. Bulk Ce L3-edge X-ray absorption spectroscopy (XAS) was performed in the biosolid before culture in order to evaluate the NMs transformation in the reactor. After the culture, elemental concentrations were measured in the plant parts by ICP-AES, and their distribution in roots by laser ablation ICP-MS. Root bacterial community structure was characterized by sequencing of 16S rRNA gene (Illumina MiSeq) in order to understand the impact of the biotransformation of CeO2 NMs on the microbiota. Our presentation will focus on how CeO2 NMs modulates the absorption of trace elements and their combined effect on the soil and root microbiota