ANR ECLAT

In French Guiana (FG), the exposure of populations living along rivers and coastal areas to trace metals and metalloids (TM) is a major concern for public health organizations. The sources of these exposures remain poorly understood. Elevated levels of potentially toxic TMs (e.g., Hg, Pb, As) in the lateritic cover (laterite and soil) result from natural accumulation over millions of years. This balance is now disrupted, on the one hand by climatic forcing (landslides, tropical storms, etc.), but especially by anthropogenic activities, foremost among which is legal or illegal gold mining, the management of pollution induced by which (notably mercury) poses a major challenge for the region. Natural or anthropogenic reshaping and erosion of lateritic covers promote the transfer of TM-rich particles into the hydrosystems of French Guiana. TMs are then subjected to numerous biogeochemical transformations that can alter their speciation toward toxic and/or bioaccumulative forms in food chains. Moreover, the addition of TMs (Pb and Hg) from anthropogenic activities (gold mining, agriculture, hunting, etc.) to a naturally high geochemical background further exacerbates the exposure risks for local populations.

The ECLAT 2024–2027 project, led by ISTerre, brings together researchers and faculty from the Geochemistry, Mineralogy, and TRB teams within the laboratory. At the national level, it involves a total of six laboratories and universities from French Guiana and mainland France to document the biogeochemical cycles of trace metals (TMs) and provide societal and public health responses to this issue in French Guiana.

Through a transdisciplinary approach (geosciences and social sciences), the project aims to understand the processes of accumulation, transfer, and fate of TMs from lateritic covers to the major rivers of French Guiana. The project will focus on two hydrosystems—the Maroni and the Mana rivers—which contrast in flow rates and water quality due to differences in population density and gold mining activities along their shores.

First, the socio-environmental and economic dynamics (gold mining, land use, etc.) of the two watersheds will be analyzed using historical archives. These results will allow the reconstruction, evaluation, and comparison of the spatiotemporal evolution of TM fluxes and anthropogenic pressure over the past two centuries.

In parallel, mineralogical, geochemical, and geochronological studies of the current lateritic covers will characterize the processes and dynamics of both geogenic and anthropogenic TM accumulation over timescales ranging from centuries to millions of years.

Finally, the reactivity of the mineral and/or organic phases carrying trace metals (once remobilized into the hydrosystems) will be studied during transport in suspension and during transient deposits (from flood events to the seasonal scale) to document the pathways and fate of these contaminants. The use of innovative methodologies (both in the field and in the laboratory), along with a diverse and complementary set of advanced tools and approaches (mineralogy, geochronology, elemental and isotopic geochemistry), will allow identification of sources and characterization of the biogeochemical processes involved in TM dynamics.