WAMP

In this project two systems will be built for the autonomous measurement of trace metal concentration in the water column and at the water-sediment interface. The two systems are based on voltammetric microelectrode arrays, so that in the two cases, the development of the sensor and voltammeter will be similar. The characteristics and innovative aspects of the two systems are the following.

The probe will be usable in the water column, down to 500m, and controlled either by an operator from a ship, or automatically by computer, when attached to a buoy. The system will have an autonomy of 1-2 weeks, and will be able to transmit automatically the data to the land station by radio, telephone or satellite communication. It will be programmable to determine concentration profiles between 0-500 m, routinely in conditions chosen by the user (time period, depth resolution, etc.). Cu(II), Pb(II), Cd(II) and Zn(II) will be measured with a sensitivity of less than 100 pM. Possible extension to the analysis of Mn(II) and Fe(II) are foreseen. The probe will allow doing 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 to get the colloidal + particulate metal fraction by difference. Emphasis will be put on the development of cheap and reliable microelectrode arrays, built by new microtechnology. Recent developments will be used combining mercury film Ir based microelectrodes, in a special antifouling gel, providing high sensitivity and long-term stability of the sensor.

A system will be built to determine concentration profiles of Pb(II), Cd(II) and Mn(II) (possibly also Cu(II) and Fe(II)) at the water-sediment interface, with submillimeter resolution. Microelectrode arrays with antifouling gel, similar to those for the water column will be used, but with individually addressable electrodes. The voltammetric probe and sensors will be placed on a lander already developed in the EUREKA EU-408 BIMS project. Measurements will be possible down to 6000m. Voltammetric data acquisition and computer control of the probe at depth will be possible. Communication and control of the probe will also be possible either by cable (at shallow depths) or by acoustic telemetry. As for the water column probe, 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 of 64 microelectrodes over a depth of 1 cm with a resolution of 100-200mm, without moving the electrode array in the sediment. For concentration profile measurements over larger depth, a micromanipulator will be used to move the electrode array vertically.

The two systems will be the first existing probes for the determination in situ, in real time, of trace metal concentration in the water column and at the water-sediment interface. They will be based on a number of advanced technologies, and will include several scientific and analytical innovative aspects. These developments will be made feasible thanks to the well-integrated complementary expertises of the four partners, namely: technology of in situ systems (IDRONAUT), microtechnologies applied to microsensors (IMT), analytical and physical-chemistry of aquatic systems (CABE), chemical oceanography (AMK).