In its pure form, ESOL has an Oxidation Reduction Potential of between +1,100mV and +1,200 mV. This creates an environment outside the working range of important microbial processes, including energy-generating mechanisms.
If immersed in ESOL, pathogens will come into contact with powerful oxidants which will sequester electrons with high efficiency from microbial structural compounds, causing the rupturing of biochemical bonds and subsequent loss of function. This is often described as an 'oxidative stress'.
In addition, the high ORP environment is thought to create an unbalanced osmolarity between the ion concentrations in the solution and that within unicellular organisms, further damaging membrane structures. This will cause increased membrane porosity, enabling oxidising moieties to penetrate (via diffusion) into the cell cytoplasm, ultimately leading to the inactivation of intracellular protein, lipids and nucleic acid, rendering the cell non-functional.
ORP is the most important factor in terms of predicting the disinfectant potential of a given ESOL solution, and this has been demonstrated experimentally by a number of researchers. The ORP of ESOL has been found to be inversely proportional to the pH, and that decreasing the pH increases the antimicrobial potential of ESOL, even if the residual chlorine levels are kept constant.
At low pH levels (pH 2–5), hypochlorous acid will be the predominant chlorine species present which is known to disrupt microbial structure and the general cellular activity of proteins. In addition, hydroxyl radicals (the strongest oxidising agent characterised) have also been detected within ESOL, and it is likely that a combination of active moieties contribute to the antimicrobial efficacy of ESOL, creating an antimicrobial milieu that has been likened to that utilised by phagosomes to induce killing within phagocytic cells of the mammalian immune system.
Oxidation Reduction Potential (ORP)
ESOL has a very large reduction potential. Reduction potential is a measure of the tendency of a chemical species to acquire electrons. Reduction potential is measured in millivolts (mV). Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons.
E. coli, Salmonella, Listeria and other pathogens have survival times of under 30 s when the ORP is above 665 mV, compared against >300s when it is below 485 mV.