Multi Physical–Chemical profiler for real-time in situ monitoring of trace metal speciation and master variables: Development, validation and field applications

This paper describes the development and the application of a submersible Multi Physical–Chemical profiler (MPCP) for in situ measurements of priority trace metal pollutant speciation and master bio-physicochemical variables. It has been designed using advanced voltammetric microsensors, microprocessor, telemetry and “smart” data acquisition and transfer technology. The MPCP allows simultaneous reliable monitoring, down to 150 m over extended period of time, of several major fractions of Cu(II), Pb(II), and Cd(II): (i) the free metal ions which are known to be related to biological uptake, (ii) the dynamic metal species which are potentially also available for organisms, (iii) the total extractable metals which represent the reservoir of metal in the test medium, and (iv) the particulate and colloidal species, by subtracting (ii) of (iii), which play important role in transport properties and residence time. In addition, it measures also pressure, temperature, pH, oxygen, conductivity, salinity, redox E, turbidity and chlorophyll a. The MPCP can be controlled either by an operator on board, in automatic mode following pre-programmed parameters, or remotely from a land station when connected to a remote controller installed in a buoy profiler or on a platform. A detailed description of the system is given. A summary of the laboratory and on-field tests performed to characterize and validate the MPCP measurements is presented. Finally, examples of attended and remote in situ MPCP monitoring/profiling in estuaries and coastal sea waters are reported. The results indicate that the system is reliable and that in situ simultaneous measurements of the three distinct fractions of trace metals can be achieved down to concentrations at the ppt level using square wave anodic stripping voltammetry (SWASV). They also demonstrated the significant advantages of the MPCP in terms of spatial and temporal resolution of data and thus its usefulness for cost effective, more efficient environmental monitoring and pollution control.