ABSTRACT

Development of submarine resource may occur pollution of mercury in the ambient seawater. It is useful if there is a handy mercury-monitoring tool for deep-sea. We developed a deep-sea mercury sensor based on an anodic striping voltammetry method. To enhance the sensitivity of the sensor to mercury in seawater, we used a large gold-ring disc with a surface area of 402 mm² as a working electrode. In addition, a propeller screw was located in front of the working electrode to create water flow and enhance the electrodeposition efficiency of the mercury. The sensor was able to detect peak current, depending on the mercury concentration in a 0.6 M sodium chloride solution in a test water container with 0.94 ng L^–1 (ppt) of the lowest detection limit (deposition time was 20 min), which was lower than 800 ng L^–1 of the lowest detection limit with an electrode surface area of 20 mm². We were then successful in in-situ measurement of mercury at the ppt level in the sea, coordinating with another measurement using the cold vapor atomic fluorescence spectrometry method. Accurate calibration was difficult for the sensor in the labo-scale. It is necessary to build another calibration method without a large volume of standard solution in the future. In addition, the sensor does not fully work in H₂S-rich environments (more than about 1 μmol L^–1) adjacent to hydrothermal fluid discharges. In spite of the weak points, this sensor will be a very useful tool for wide-range monitoring mercury in seawater.