Processes controlling the environmental dynamics and societal impacts of Geogenic and Anthropogenic trace metals contaminants in French Guiana – ECLAT

In French Guiana (FG), the exposure of populations living along rivers and coastal areas to trace metals and metalloids (TMs) is a major concern for public health organizations. Today, the origin of these exposures still remains poorly understood. The high levels of potentially toxic TMs (e.g., Hg, Pb, As) in lateritic covers (laterite and soil) result from a natural accumulation over millions of years. This equilibrium is today disturbed on the one hand, by climatic forcing (landslides, tropical storms...), but above all by anthropogenic activities, first of all legal or illegal gold mining, which induced pollution (notably mercury) constitutes a major challenge for this territory. The reworking and erosion (natural or not) of lateritic covers favor the transfer of particles enriched in TM into the Guyanese hydrosystems. The TMs are then subjected to numerous biogeochemical transformations that can modify their speciation towards toxic and/or bioaccumulative forms in the trophic chains. On the other hand, the addition of TMs (Pb and Hg) from anthropogenic activities (gold mining, agriculture, hunting...) to a naturally high geochemical background exacerbates the risks of exposure of populations.
The ECLAT project federates 6 laboratories and universities located in French Guiana and in mainland France to document the biogeochemical cycles of TMs, and to provide societal and public health responses to this problem in French Guiana. Through a transdisciplinary approach (geosciences and social sciences), the project will focus on understanding the processes of accumulation, transfer, and fate of TMs from lateritic covers to the large Guyanese rivers. The project will be carried out on two hydrosystems; the Maroni and the Mana, which are contrasted by their water flows and the quality of their waters due to a very different density of population and gold mining activity on their shores. First, the socio-environmental and economic dynamics (gold mining, land use...) of the two watersheds will be analyzed on the basis of historical archives. These results will allow to evaluate, reconstruct and compare the spatiotemporal evolution of TM fluxes and anthropogenic pressure over the last two centuries. In parallel, the mineralogical, geochemical and geochronological study of current lateritic covers will allow to characterize the processes and dynamics of geogenic and anthropogenic TMs accumulation on time scales ranging from century to million years. Finally, the reactivity of mineral and/or organic carrier phases of TMs (once remobilized in hydrosystems) will be studied during suspended transport and during transient deposition events (from the flood to the seasonal scale) to document the pathway and fate of these contaminants. The use of innovative methodologies (field and laboratory), various and complementary scopes and tools (mineralogy, geochronology and elemental and isotopic geochemistry) will allow the identification of sources and the characterization of biogeochemical processes involved in TM dynamics. This project will bring a new vision of this complex socio-ecosystem, and answers to the society on the risks of exposure to TM. The dissemination of knowledge (workshop, teaching, dissemination via GIS, and popularization of results) to the University of French Guiana, state agencies and the general public will allow the Guyanese population to access qualitative and quantitative information on the impact of (il)legal mines and on the exposure of populations over time. The ECLAT project will therefore allow for better management of the environment and human health and increase the development of education on this issue.