Annual inorganic mercury speciation in river water disturbed by chlor-alkali effluents: role and competition of ligands (Cl-, Br-, DOC)

We used Cold Vapor Atomic Fluorescence Spectrometry to determine the annual evolution of the mercury speciation in a watershed disturbed by chlor-alkali effluents. Throughout the year, the river water is enriched in chloride, bromide and DOC due to punctual and diffuse industrial and domestic activities. Moreover, mercury concentrations are 50 to 100 times higher than the natural waters downstream to the chlor-alkali effluents. The hydrological regime and the water chemistry play an important role in the mercury speciation. During high water periods, the hydrological conditions (discharge, suspended sediment content and water temperature) may control the mercury partitioning in the river water, the pollutant being mainly adsorbed onto suspended particles. On the other hand, during the summers’ low waters, higher concentrations in chloride, bromide and DOC may lead to form stable Hg-Cl, Hg-Br and Hg-DOC complexes in the aqueous phase, facilitating the mercury percolation towards the groundwater