EC2CO project

**Isotopic tracing of metal transfers (Zn, Cu) in a structure retention-infiltration

The general objective of the proposed project is to quantify metal flows through a retention-filtration structure in an urban context by including the role of spontaneous vegetation in situ. We propose an exploratory study of the natural variations in the concentration and abundance of stable isotopes of Zn and Cu as a tracer of the sources and bio-chemical processes of storage and transfer of these metals at the CBR pilot site.

The choice of these two metals is justified by the continuous presence of their emission and concentration in the environment due to human activities. In addition, they are two trace elements that are essential for life but can become toxic at high concentrations. The first aspect of the project will focus on the identification and quantification of sources of metallic pollutants. The aim will be to characterize in an urban context, in the work studied, the sources of Cu and Zn by their isotopic ratios in order to quantify, if possible, their input contribution and to monitor their future through the work.

A potential tool for defining sources of metal pollution is the use and coupling of isotope ratios of Zn and Cu. A second question concerns the quantification of metal fluxes at the soil structure interface, including vegetation, using stable isotope ratios of metals. The aim will be to characterize the overall metal removal by vegetation through the structure and the dynamics of the metal in the soil/plant system.

In a first step, we propose to determine the isotopic fractionations associated with the bio-chemical transfers and storage between the main Zn and Cu reservoirs (extraction of the bioavailable metal, extraction of the metal by plants, precipitation or adsorption at the root-soil interface, transfer and storage forms of the metal in the underground parts, translocation of the metal from the root to the overhead parts, recycling of the overhead parts in the litter).

The coupling between EXAFS spectroscopy, chemical extraction and isotopic approach will make it possible to document the changes in the chemical form of the metal between the tanks in connection with the transfer of these metals and the differences in isotopic composition observed. A first quantification of metal flows at the groundwork interface (including vegetation) will be carried out using elementary and isotopic balances of metal transfers.