Isalyne BLONDET - Development and application of passive samplers for mercury speciation in marine waters

Mercury (Hg) is a naturally occurring metal whose concentrations have been greatly amplified by human activities, notably artisanal gold mining and coal combustion. This global pollutant is transported through the atmosphere, soils, and aquatic environments, where it undergoes numerous biogeochemical transformations. Among these, the formation of monomethylmercury (MMHg) is of particular concern: this neurotoxic compound accumulates and biomagnifies along marine food webs, exposing humans through seafood consumption. Despite the Minamata Convention (2013), understanding of the marine mercury cycle remains limited due to ultra-trace concentrations (<1 ng.L*") and the high cost of conventional discrete sampling. My thesis evaluated the potential of passive samplers based on Diffusive Gradients in Thin Films (DGT) for monitoring in marine waters. DGT devices integrate concentrations over days to weeks, providing time-weighted averages more representative of geochemical background than discrete sampling. The main objective is to overcome analytical constraints limiting DGT application to mercury monitoring. An automated in situ cleaning system, the "miniwiper," was designed to limit biofouling and particulate accumulation during long deployments, essential for detecting ultra-trace concentrations. Tested in productive Peruvian coastal waters, it reduced biofilm and particle deposition on DGT membranes.