In-situ trace metal (Cd, Pb, Cu) speciation along the Po River plume (Northern Adriatic Sea) using submersible systems

Highlights • In-situ trace metal speciation in the Adriatic Sea by submersible voltammetric sensors • Metal species distribution mainly affected by Po River outflow. • Metal dynamic concentrations below legal limits • Cu dynamic concentrations toxic to sensitive phytoplankton Abstract Information on the distribution and speciation of trace metals is of critical importance for our ability to interpret the links between the bioavailability and uptake of an element, and its biogeochemical cycle in coastal environments. Within the framework of the European Project “In-situ automated Monitoring of Trace metal speciation in Estuaries and Coastal zones in relation with the biogeochemical processes (IMTEC)”, the chemical speciation of Cd, Pb and Cu was carried out along the Po River plume in the period 27 October – 2 November 2002. During the cruise, five Voltammetric In-situ Profiling systems and one Multi Physical Chemical Profiler, as well as conventional voltammetric instruments, were successfully applied in order to evaluate the distribution of Cd, Pb and Cu between different fractions (free ion, dynamic, colloidal, dissolved and particulate fractions) and to assess the evolution of these fractions during estuarine mixing and in the water column. Dynamic concentrations were 0.05–0.2 nmol L−1 Cd, 0.02–0.2 nmol L−1 Pb, and 0.15–4.0 nmol L−1Cu. Cd was mainly present as dynamic fraction (40–100% of the dissolved Cd). High proportions of Pb (~70%) and Cu (~80%) were present as colloids probably of biogenic origin. Principal components analysis reveals a strong influence of the Po River discharge on the spatial and vertical distributions of metal species. Almost all the metal fractions globally decreased following the salinity gradient. Metal concentrations are far below (at least one order of magnitude lower) the Environmental Quality Standard established by the Italian law. However, the Cu dynamic fraction showed concentrations likely to be toxic to sensitive phytoplankton community and to have negative effects on larva development of coastal macroinvertebrate species (toxicity data extracted from literature)

Electrochemical methods for speciation of trace elements in marine waters. Dynamic aspects

The contribution of electrochemical methods to the knowledge of dynamic speciation of toxic trace elements in marine waters is critically reviewed. Due to the importance of dynamic considerations in the interpretation of the electrochemical signal, the principles and recent developments of kinetic features in the interconversion of metal complex species will be presented. As dynamic electrochemical methods, only stripping techniques (anodic stripping voltammetry and stripping chronopotentiometry) will be used because they are the most important for the determination of trace elements. Competitive ligand ex- change-adsorptive cathodic stripping voltammetry, which should be considered an equilibrium technique rather than a dynamic method, will be also discussed because the complexing parameters may be affected by some kinetic limitations if equilibrium before analysis is not attained and/or the flux of the adsorbed complex is in fluenced by the lability of the natural complexes in the water sample. For a correct data interpretation and system characterization the comparison of results obtained from different techniques seems essential in the articulation of a serious discussion of their meaning

Complexing gel integrated microelectrode arrays for direct detection of free metal ion concentrations in natural waters

A novel Complexing Gel Integrated Microelectrode (CGIME) for direct measurements of free metal ion concentrations in natural waters has been developed. It is prepared by successive deposition of a chelating resin, antifouling agarose gel and the Hg layers on an 100-interconnected Ir-based microelectrode array. Reliability of trace metal accumulation on the chelating resin and their release in acidic media and detection using Square Wave Anodic Stripping Voltammetry bas been demonstrated by a series of replicate laboratory tests. Finally, the CGIME sensor has been applied to the Cu and Pb free metal concentration measurements in sea water samples. The CGIME results were comparable with those of free metal ion concentration measurements performed using Hollow Fiber Permeation Liquid Membrane (HF-PLM). Similar concentration values were found for both metals with both techniques which validate CGIME measurements

Application of 3-way Principal Component Analysis to water quality assessment of the Venice lagoon

none4R. LEARDI; M.L. TERCIER-WAEBER; B. GIANNI; G. FERRARILeardi, Riccardo; M. L., TERCIER WAEBER; B., Gianni; G., Ferrar

Individually addressable gel-integrated voltammetric microelectrode array for high-resolution measurement of concentration profiles at interfaces

The application of a novel voltammetric probe, based on an individually addressable gel-integrated microelectrode array (IA-GIME), for real-time, high-spatial resolution concentration profile measurements at interfaces is described. Reliability and validity of steep metal concentration gradients obtained with this novel system have been demonstrated by performing systematic tests at well-controlled liquid-liquid and liquid-solid interfaces. The liquid-liquid interface was formed by two layers of aqueous solutions with different components; only one layer contained trace metal ions (Pb(II) and Cd(II)); the individually addressable microelectrode array was placed at the interface of the liquid-liquid system; the concentration profiles were recorded as function of time; and the effective diffusion coefficients were calculated. The liquid-"solid" interface was formed from an aqueous solution layer overlying a bed of silica particles saturated with an aqueous solution. The sensor array has been used to monitor the diffusion processes of Tl(I) or Pb(II) from the liquid phase to the "solid" phase. The influences of porosity, geometry of the porous media, and complexation between metal ion and silica, on the diffusion processes, have been studied. All these results show that correct diffusion profiles of metal ions at interfaces can be obtained with 200-μm resolution with the IA-GIME. They also demonstrate that, for measurements in "solid" phase, the aforementioned factors must be considered carefully for correct calibration of any electrodes and the gel-integrated microelectrodes are unique tools to enable calibration of the sensors with synthetic solutions