VARIABILITY OF DISSOLVED MN AND ZN IN THE SEINE ESTUARY AND CHEMICAL SPECIATION OF THESE METALS IN SUSPENDED MATTER

A general study of manganese and zinc in both dissolved and particulate forms in waters from the Seine river, its estuary and the Bay of Seine (in northern France) has been undertaken in order to investigate their fate and transport processes in riverine, estuarine and coastal environments. These samples have been analyzed using graphite-furnace atomic absorption spectroscopy (GFAAS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and differential pulse anodic stripping voltammetry (DPASV). In this work, we have considered the different parameters (salinity, pH, temperature and total suspended matter) which may influence the metal distribution in the estuary, and have surveyed the evolution of these metals (with numerous soluble organic and inorganic ligands) in aqueous phases and their interaction with the various inorganic and organic solid fractions which compose the particles. The results show that dissolved Mn and Zn are mainly influenced by salinity. Furthermore, their variability is governed by temporal and spacial changes in tidal stress. Indeed, the distributions of dissolved Mn and Zn are linked to the internal properties of particles and the flow of sediments regulated by the tidally-induced perturbations in the estuary bed. Since the cause of these observations is in connection with the interactions between the liquid phase and the solids present, we have also undertaken the chemical speciation of Mn and Zn in the particles. The results obtained confirm the non-conservative behavior of these two metals. Owing to the paramagnetic properties of Mn, we have been able to analyze particles using electron spin resonance spectroscopy in order to gain further information about the nature of Mn compounds, their oxidation states and their combinations.