Mercury electrode as a tool/sensor for pollutants monitoring in natural waters; advantages and disadvantages regarding moving to “green” electrochemistry

Green Chemistry or Sustainable Chemistry is defined by the EPA1 as “the design of chemical products that reduce or eliminate the use of hazardous substances”. In recent years there are great expectations that chemists will produce greener and more sustainable chemical processes. In this direction, relevant benefits from “green” electrochemical activities (better control, higher selectivity, safer operations, milder conditions, and the use of electrons as a cheap reagent) were found. Some important instances of “green” electrochemistry are detectors and bio-detectors for environmental analysis (detection of pollutants). Since the invention of polarography, the Hg electrode was established as the preferred electrode for use in electrochemistry due to the high over potential for hydrogen evolution (which enables work at moderately negative potentials), as well as renewability of the electrode surface.2 The current trend of “green” chemistry, that encourages avoiding the use and generation of toxic substances, as well as recent EU regulations that have prohibited exporting and storing metallic Hg, have led to the search of competitive electrodes fabricated with minimal amount of Hg or definitely with other materials. However, in comparison to solid electrodes, Hg has many advantages which cannot easily be ignored and replaced in the move towards “green” electrochemistry by use of solid electrodes when characterizing the surface active (SA) fraction of organic matter as well as sulfur species in natural waters.2–6