Two systems will be built for the autonomous measurement of trace metal concentrations in the water column and at the water-sediment interface. They are based on voltammetric microelectrode arrays, so the development of the sensor and voltammeter will be similar.
VOLTAMMETRIC PROBE FOR THE WATER COLUMN, usable in the water column down to 500m, and controlled either by an operator from a ship, or automatically when attached to a buoy. The system will determine concentration profiles between 0-500 m, routinely in function of time and depth for 1-2 week and will be able to transmit the data to a land station by radio, telephone or satellite link. Cu(II), Pb(II), Cd(II) and Zn(II) will be measured with a sensitivity less than lOOpM. Extension to the analysis of Mn(II) and Fe(II) are foreseen. The probe will allow metal speciation: it determines specifically the "truly dissolved" fraction of the trace metals (i.e. metal species smaller than ca 3 nm), directly in situ, without any sample handling thus minimizing methodological artefacts.
Additional determination of the total metal concentration allows definition of the colloida]+ particulate metal fraction by difference.
Emphasis will be put on the development of cheap and reliable microelectrode arrays, uilt using new microtechnology.
Recent developments in combining mercury film Ir based microelectrodes, in a special antifouling gel, providing high sensitivity and long-term stability of the sensor will be used.
SEDIMENT-WATER INTERFACE MICROPROFILER, to determine concentration profiles of Pb(II), Cd(II) and Mn(II) (possibly also Cu(II) and Fe(II)) at the sediment-water interface, with submillimeter resolution. Microelectrode arrays with antifouling gel and with individually addressable electrodes will be used. The voltammetric probe and sensors will be placed on a lander already developed in the EUROMAR EU-408 BIMS project. Measurements down to 6000m will be stored or transmitted by cable (shallow depths) or by acoustic telemetry. The truly dissolved (i.e. the mobile) fraction of metals will be measured. A multipotentiostat and multiplexer will be combined to record the concentration profiles in 64 microelectrodes over a depth of 1 cm with a resolution of 100-200um without moving the electrode array in the sediment or a micromanipulator will be used to move the electrode array vertically. THE TWO SYSTEMS will be the first existing probe for the determination in situ of trace metal concentration in the water column and at the sediment -water interface.The tecniques to be used are feasible thanks to the well-integrated complementary expertise of the four partners.
Funding SchemeCSC - Cost-sharing contracts
412 96 Goeteborg
1211 Genève 4