Transfer of a method for assessing the residual exposure to contaminants after an ecological restoration operation (Biogeco/City of Bordeaux)*
The purpose of the EXPOMETAL project is to transfer a method for monitoring contaminants in the soil pore water through the use of rhizon-type passive sensors by the technical services of the City of Bordeaux. By using this technique within the context of a routine use, they will get more realistic information, and at a lower cost, about the evolution of the contamination in the contaminated sites that they manage.
In 2013, the City of Bordeaux requested the expertise of Mr. Mench (DR. INRA, BIOGECO) and L. Marchand (post-doc, BIOGECO) for an expert assessment in ecological restoration on the outlet of the new Chaban-Delmas bridge, linking the right bank of the Garonne River to the left bank at the Port de la Lune. In order to identify the risks related to the exposure to metals and hydrocarbons, the city of Bordeaux has enlisted the help of the Joint Research Unit BIOGECO to establish a diagnosis of the contamination of the site and propose an ecological restoration of the area aimed at reducing the exposure of biological receptors, including humans, to contaminants. This project was implemented in spring 2013.
The first step to assess the success of such a process classically comprised a follow-up of the total pool of contaminants * present in the soil. However, in the short term, it is not this total pool which is impacted by the biological activity linked to the establishment of the vegetation cover, but the fraction in bioavailable contaminants. **
For its research, the BIOGECO laboratory used the measurement of contaminant levels in the pore water as an indicator of this bioavailable fraction by using passive sensors (Rhizons and DGT). This targeted approach provides a much better account of the role of the plants/microorganisms assemblage in the initiation of a decontamination process.
* Set of contaminants, both mobile and immobile, present in a soil
** Fraction of mobile contaminants, likely to be transferred to biological receptors