Environmental Enlightenment #162
By Ami Adini -
Reissued May 4, 2016

This is a SHORT, LIGHT and SIMPLE newsletter. Its purpose is to rekindle in the initiated terminology they have once learned, and enlighten the uninitiated on terms they may have heard but never known the meaning of.

The Oxidation-Reduction Potential

Potential means “the inherent capacity for coming into being.” You see a child kicking legs in the air and you say, this one has a  potential for becoming a champion in karate.

Potential also means “existing in possibility.” One looks at Mount St. Helens steaming and says, there is a potential for volcanic eruption.


In electricity it means the difference in electrical charge between two points. This difference creates a possibility of discharge from the highly charged point to the lesser charged point.

In the illustrations above, interactions between thunderclouds and air cause electrical energy to accumulate in parts of the clouds close to earth. As these electrical charges accumulate, they press to go and when the cloud comes low, they discharge to the ground; like a crowd pressing against locked gates. With enough pressure, the gates break open and the crowd rushes in.

This electrical pressure to discharge is a potential, and in electricity we measure it in units called Volts, after the Italian physicist, Conte Alessandro Volta (1745-1827), Professor of Physics at the University of Pavia from 1779.  
  The volt is the pressure that pushes the current down the line through the lamp.

Oxidation is the action of combining with oxygen. When an element joins with oxygen, it loses electrons to the oxygen. We expand the concept and say that any time a substance loses electrons; it is “oxidized,” regardless of whether it lost the electrons to oxygen or to another element or compound. Chlorine, for example is very attractive to electrons, thus a strong oxidizer.

Reduction is the reverse of oxidation. It is a reaction in which atoms or molecules either lose oxygen or gain electrons. Oxidation and reduction always happen together: an oxidizer (oxidant) is being reduced and a reducer (reductant) is getting oxidized. When oxygen combines with hydrogen to make water, the hydrogen is oxidized and the oxygen has been reduced.

The oxygen is hungry for electrons and the hydrogen cannot hold strong enough to its single electron in the presence of such a strong affinity. They end up bonding together in the common share of electrons.

ORP stands for Oxidation-Reduction Potential. In some parts of the world, it is also known as Redox Potential. The two chemical reactions are really "joined at the hip" - one cannot occur without the other also occurring.

Chemicals like pure oxygen, ozone, hydrogen peroxide, sodium persulfate and sodium permanganate crave electrons, always; they are all oxidizers.

It is their ability to oxidize - to "snatch" electrons from other substances - that makes them good decontaminators of groundwater that is polluted with petroleum products; because, in altering the chemical makeup of the unwanted pollutants they "burn them up," leaving carbon dioxide and water as the by-product.

Of course, in the process of oxidizing, all of these oxidizers are reduced - so they lose their ability to further oxidize things. To make sure that the chemical process continues to the very end, you must have a high enough supply of oxidizer in the water to do the whole job.

But how much is "enough?" That's where the term Oxidation-Reduction Potential (ORP) comes into play.  In talking about ORP, we are actually talking about electrical potential or voltage. We are reading the very tiny voltage generated when a metal is placed in water in the presence of oxidizing and reducing agents.

These voltages give us an indication of the ability of the oxidizers in the water to burn off the contaminants.

If we had a body of water in which the total electron-attraction power of the oxidizers exactly equaled the total electron-giving “weakness” of the reducers (e.g. the polluting chemicals), then the amount of potential generated at the measuring electrode would be exactly zero. The water would be in pretty sad shape, because if any additional contaminants were introduced into the water, there would be no oxidizer left to handle it—all have been “spoken for.”

Through the measurement of Oxidation-Reduction Potential we monitor the oxidation of the pollutants to the achievement of our groundwater cleanup objectives.

You can find past issues of "Environmental Enlightenment" at www.amiadini.com - A wealth of information about environmental site assessments in the real estate transactions and issues concerning assessment and cleanup of contamination in the subsurface soil and groundwater.

Call me if you've got any questions. There are no obligations.

Ami Adini & Associates, Inc.
Environmental Consultants
Underground Storage Tank Experts
818-824-8102; 818-824-8112 fax

Ami Adini is a mechanical engineer, California Registered Environmental Assessor, Level II, and president of AMI ADINI & ASSOCIATES, INC. (AA&A), an environmental consulting firm specializing in all phases of environmental site assessments, rehabilitation of contaminated sites and upgrading of underground storage tank facilities. AA&A supplies practical solutions to environmental concerns using the highest standards of ethics and integrity while providing its clients with maximum return on their investments.