Description du sujet de thèse

Implementation of advanced speciation methods for the study of selenium contrasting bioavailability at the territorial level
Selenium (Se) is an essential micronutrient that can become toxic within a very narrow concentration range. It originates from natural processes of mineral weathering and volcanic activity, in addition to anthropogenic contributions (industrial and agricultural uses). Soils represent an important reservoir of selenium and the main source of its transfer to the vegetation. The ability of plants to take up selenium is quantified by the soil-plant transfer factor, i.e., the ratio of total selenium concentrations in plant and soil. However, in this calculation, the internal and external characteristics of the soil as well as their influence on selenium bioavailability are not taken into account.
The transfer factors values reported in the literature for selenium thus vary from 0.1 to 100 depending on plant species, target part of plant, soil properties and the chemical form of Se supplied to the soil or the solubility of those initially present in the soil. The first data available for soils of the territory considered in this study indicate total selenium levels that are rather homogeneous and classical, but nevertheless associated with transfer factors that can vary by 2 orders of magnitude. At the scale of this given territory, areas with contrasting bioavailability of Se for the vegetation therefore seem to coexist independently of the total Se content in the soils. In this context, the objective of this project is to understand the biogeochemical processes involved in this amplification of Se bioavailability.
To this end, this project will aim to :
- characterize and compare the distribution and the speciation of selenium in soils associated to the extremes of transfer factor values,
- conduct an in-depth study of Se transfers via monthly monitoring over one year of the different compartments: rainwater, groundwater, soil water, soil solid phase, vegetation and, air to obtain quantitative and qualitative description of Se cycling in area where its bioavailability is increased.

Contexte de travail

The candidate will work at the Institut des sciences analytiques et de physico-chimie pour l'environnement et les matériaux (IPREM), a joint CNRS/UPPA research unit (UMR 5254). More specifically, he/she will be a member of Environmental Chemistry and Microbiology Cluster (CME Cluster), whose research focuses on understanding the mechanisms (physico-chemical and (micro)biological) at different scales (from the molecule to the ecosystem) that control the fate and the effects of trace elements and contaminants in the environment. To achieve the set objectives, the project will be supported by laboratory's instrumental facilities (including HPLC/GC-ICPMS) and the scientists involved (David Amouroux, Maïté Bueno, François Rigal et Emmanuel Tessier). This project is carried out in collaboration with Andra.

The candidate must have a Master's degree in analytical chemistry or environmental sciences with an interest in biogeochemistry. He/she is passionate about environmental issues, rigorous and highly motivated. Experience in analytical development and metal speciation would be a plus. The candidate must have a good level of English and the ability to work independently.

Contraintes et risques

Travel will be required to the study site in Meuse/Haute Marne for sampling and field experiments. The candidate will then work outdoors, in weather conditions that may be difficult depending on the season.