Multiscale Investigation of The Mechanisms - Aix-en-Provence, France - CEREGE, Sustainable environment team

Description

Multiscale investigation of the mechanisms controlling cadmium's phytoavailability in durum wheat and potatoes: soil/plant transfer and fate:

• Réf

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ABG-114373

• Sujet de Thèse 11/05/2023
• Contrat doctoral
• CEREGE, Sustainable environment team
• Lieu de travail
• AixenProvence
• Provence-AlpesCôte d'Azur
• France
• Intitulé du sujet
• Multiscale investigation of the mechanisms controlling cadmium's phytoavailability in durum wheat and potatoes: soil/plant transfer and fate
• Champs scientifiques
• Ecologie, environnement
• Agronomie, agroalimentaire
• Mots clés trace element, plant, isotopes, speciation
  Description du sujet:
• Context _

According to the Food and Agriculture Organization of the United Nations, the world population will reach 9 billion people by 2050.

Feeding humanity will require an increase of 70% of food crop production and will strain the agricultural soils. Anthropogenic soil fertilization enhances productivity.

However, the use of fertilizers comes at a price, as depending on their nature, they can bring toxic contaminants to the system.

Heavy metals and metalloids, such as cadmium and arsenic, have a high affinity for phosphates and are found in phosphate fertilizers.

Cadmium is an ecotoxic heavy metal that bioaccumulates throughout the food web.

In the past 150 years, its biogeochemical cycle has been completely altered by anthropogenic activities releasing Cd in the environment, namely fossil fuel combustion, non-ferrous metal smelting, and the use of inorganic phosphate fertilizers1.

Cadmium contamination of agricultural soils is of particular concern as it has a relatively high mobility in soils and soil/plant systems and shows acute toxicity toward almost all forms of life1, even at low concentrations2.

Cadmium intoxication is a matter of public health:

Cd is classified as a carcinogen and causes major body dysfunctions, such as kidney failure, serious damages in lungs, cerebrovascular infarctions, osteoporosis, and its intake must be controlled.

The European Food Safety Authority (EFSA) has proposed a maximum weekly intake of 2.5 μg.kg-1 for an adult3, and a majority of the European population is already overexposed to Cd4.

Europeans are exposed to Cd through massive consumption of cereals and vegetables products with moderate Cd content rather than via the episodic consumption of heavily contaminated products (_e.g. _algae, cocoa). In Europe, most of the Cd intake via food is due to products derived from potatoes and durum wheat- Goals_

To limit Cd content in crops, actions can be conducted on three main fronts: (i) limit the soil Cd diffuse contamination, (ii) limit Cd transfer from the soils to the crops and (iii) limit Cd content in the edible parts of the plant.

The main goals of this PhD project are set in the axes (ii) and (iii).

We propose to investigate the processes that control the Cd transfer from agricultural soils to potatoes (_Solanum tuberosum_) and durum wheat (_Triticum durum_) - and therefore its phytoavailability - as well as its fate in the crop (_e.g._ translocation, detoxification, root storage).

Cadmium's mobility and bioavailability depends _in fine_ of its speciation, which will be described at the atomic scale throughout the project.

The project relies on an original and innovative approach to better constrain Cd's fate in crops, that will combine two cutting-edge technologies: stable isotope mass spectrometry and experimental determination of speciation by X-ray absorption spectroscopy5,6.

Isotopes can be used to trace sources and fluxes, as well as chemical reactions and mechanisms in plants. XAS spectroscopy allows for direct determination of Cd speciation in plants, when above the detection limit (> 2ppm).

The combined use of these two technologies will help shed light on the links between isotopes and speciation and bring new constraints on the mechanisms controlling Cd's fate in the crops.

Taking advantage of the individual and combined strength of these two techniques, the overarching goal of this project is to investigate the following:

• How is Cd transferred from the agricultural soils to _Solanum tuberosum_ and _Triticum durum_? Which Cd species are the most phytoavailable? What are the main controlling parameters (_e.g._ soil composition, cultivar)?
• What is Cd's fate in the plant: translocation, diffusion in the saps, storage, detoxification? What factors may favor the immobilisation (storage) and/or detoxification of Cd in non-edible parts of _S. tuberosum_ et _T. durum _?
• Workplan_
• Part plant cultures in a controlled environment_

To test the role of various soil parameters (_e.g. _pH, C content) on Cd phytoavailability, crop culture will be performed on soils from experimental farm plots representative of European agricultural soils. Several wheat and potato cultivars will be tested.

• Part
• Location and speciation of Cd in the crop: insights from Xray analysis on Cd's fate in the