The overall focus of my research concerns the study of interactions between major and trace elements and major constituents of water, soil and sediment biogeochemical cycles.

Continental surfaces are the locus of significant transfers and exchanges of matter. At the watershed scale, these transfers are made in a large geochemical cycles: weathering of rocks - transport by rivers - sedimentation - diagenesis. To understand these transfers and for instance the environmental role of organic matter, it is necessary to determine the speciation of mobilised chemical elements: dissolved, colloidal, and / or solid. The adsorption and complexation of major and trace elements by finely divided materials (i.e. colloidal minerals, organo-mineral and purely organic) influence their transfer processes in rivers and soils.

These natural materials are oxides or oxy-hydroxides, and organometallic metal (Fe, Si, Al, organic matter) or polydisperse organic macro-molecules. They are characterised by a very large surface area, high reactivity and high surface charge. These properties make these materials very important for the transfer of vital and toxic elements and also play a key role during weathering processes. They are ubiquitous and have properties that vary over time and depending on the physico-chemical properties encountered during their migration. Among these materials, organic colloids play an important role in the biogeochemistry of major and trace elements. They can significantly affect the speciation and increase the mobility of elements, even the most insoluble.

Since the beginning of the 19th century, global biogeochemical cycles of many metals are to a large extent controlled by anthropogenic activities such as sewage, agricultural and industrial inputs. Once released into water, the pollutant is associated with various components present in the environment that are most often distinguished by their size and nature. The association between the micro pollutant and the various constituents of the process depends on competition between functional groups or adsorption sites carried by each constituent (i.e. organic moieties versus mineral surfaces). Understanding changes in speciation of pollutants in a geochemical cycle involves knowing its reactivity with respect to the various compartments (mineral, organic, biological) that can be classified into solid substrates, species in solution, colloidal species and / or particulates.

Fixation in soil micro-nutrients, trace metals, pesticides and other toxic compounds by organic matter and clay minerals and oxy-hydroxides controls the steady-state chemical soil or sediments (Chemo-stat), bioavailability and mobility of these compounds.

In many parts of the globe micronutrient deficiencies limit plant growth and thus crop yields. In industrialised countries the use of fertilisers partly solves this problem. Unfortunately the solution of this problem leads to a deficiency of over-abundance of micronutrients and soil pollution due to intensive use of fertilisers or pesticides and the discharge of pollutants resulting from industrial activity. To understand and analyse the future of micro-nutrients and risks posed by the presence of toxic compounds (micro-metal pollutants) the nature and form of their interactions (sorption, desorption, precipitation) with the solid phase of soil or sediments (organic matter, minerals) and the colloidal phase of the pore water must be well understood.

The aim of my work is to contribute to this understanding by focusing on the role of soil or sediment organic matter (SOM) and water (DOM). The work I do is put thus in the general study of biogeochemical processes at interfaces that play a major role in water-soil or water sediment systems.

I am currently involved in the following research topics :

Topic 1
* Thermodynamic modelling of trace elements and contaminants (including nano-particles) sorption: Cation exchange and structurally based surface complexation theory; application to organic matter, clays, oxides and mixed mineral systems. Coupling into reactive transport models. Applications Fe, Al, Zn, Pb, Cd, ZnO, TiO2, CdS, CdSe.

Topic 2
* Geochemistry of radio-active waste disposal environments : Radionuclide fate and interactions with natural colloids. Janot et al., 2010

Topic 3      

* Natural organic matter in aquatic systems: Structure, composition, reactivity and fate. Application to amazonian rivers Natural organic matter.  Alasonati E., et al. 2010      

Topic 4
* Early weathering stages: Chemistry of rivers and streams flowing on freshly exposed rocks (basalts), implications for weathering processes and global carbon cycle in Guadeloupe island. Lloret et al 2010