February 2005

Chlorinated isocyanurates (Eye-so-sigh-AN-your-eights) are a family of chlorine disinfectants used commonly to destroy germs and algae in pools and spas. They are also a sanitizing ingredient in automatic dishwasher detergents and other cleaning products. And where clean drinking water is unavailable due to poverty or natural disaster, chlorinated isocyanurates, in the form of granules or tablets of solid powder, can be used to disinfect water for household or emergency use.

Hypochlorous Acid

When mixed with water, chlorinated isocyanurates unleash a powerful germ-buster--hypochlorous acid, HOCl. Composed of hydrogen, oxygen and chlorine, hypochlorous acid is also released in water, by other chlorine disinfectants, including liquid sodium hypochlorite (chlorine bleach), solid calcium hypochlorite and chlorine gas. Because it is the active germ-killer in chlorine disinfectants, the amount of hypochlorous acid released in water--known as the "free available chlorine"--is an important measure of the effectiveness of these compounds. Chlorinated isocyanurates typically contain between 56 and 90 percent available chlorine, depending upon the specific chlorinated isocyanurate compound used.

Chlorinated isocyanurates and calcium hypochlorite are solid compounds at room temperatures. Storage and transport of solids is relatively easy, so these compounds are commonly used to sanitize pools and spas and household and emergency water supplies.

Smart Use of Chlorinated Isocyanurates

Studies show that chlorinated isocyanurates have a special advantage in controlling germs in outdoor swimming pools. Because of its unique chemistry, chlorinated isocyanurates release hypochlorous acid in water slowly, as it is needed, not all at once. This is very helpful because UV radiation in sunlight is known to break down hypochlorous acid in pool water, making it ineffective as a germ-killer. The slow release of free available chlorine from chlorinated isocyanurates means they are resistant to UV radiation-a plus for swimmers' health. Because of this helpful property, chlorinated isocyanurates are often referred to as "stabilized chlorine."

Approximately 100 years of experience chlorinating drinking water demonstrates that when safe, abundant drinking water is made available to communities, cases of waterborne diseases decline, the quality of life increases, and people live longer. Disinfecting the drinking water of developing nations and populations coping with disasters is, therefore, an important public health goal.

Water and Cells

The human body is a collection of billions of cells-tiny, watery sacks containing the chemicals of life, including proteins, carbohydrates, DNA and more. To function properly, living cells must remain sufficiently watery, or hydrated, so that critical chemical reactions, such as those that give us energy, can occur. That is why access to clean drinking water is one of the most basic requirements of human health.

There are many places in the world where clean drinking water does not flow freely from the kitchen faucet. In these lands, much of a family's energy and time are spent hauling water home for drinking, cooking and bathing. Instead of going to school, many children spend hours every day carrying water-water scooped from streams or wells-water that, in many cases, is contaminated with germs that cause life-threatening illness. And when disaster strikes in the developing world or anywhere-hurricanes, floods and earthquakes-and the recent South Asian tsunami--drinking water may become contaminated, posing a serious risk to people trying to cope with sudden misfortune.

Until water treatment and delivery systems can be built in poor communities, and wherever emergency water supplies are needed, water purification kits containing chlorinated isocyanurates can be used to help protect public health.

Penetrating Germ Cell Walls Using a Watery Disguise

Just as the human body is a collection of cells (see The Gallery of Cells), germs, such as bacteria, that live in water and cause disease, are also made of cells. Cell walls are made of porous material that regulate the passage of material in and out of the cell. Water and nutrients seep into cells and water and waste products seep out.

As the figure of "Ted" the water molecule indicates, the water (H2O) molecule is shaped like a teddy bear head, with one oxygen atom forming the face and two hydrogen atoms, the ears of a bear. Hypochlorous acid is structured very similarly, with an "oxygen face" but with two different atoms, hydrogen and chlorine, for ears. (It's basically Ted with a hugely swollen ear!) Because its chemical structure is similar to that of water's, "Harry," the hypochlorous acid molecule, manages to slip, chemically undetected, into the enemy territory of germ cells. Once inside the germ cell, Harry destroys it chemically, helping to make drinking and recreational water safe.

Follow-up Questions:

  1. Add to the Gallery of Cells sketches of: human nerve cells, connective tissue cells and cartilage cells.

  2. Sketch and label the main components of a cell.

  3. How does the effectiveness of chlorinated isocyanurates vary with pH ?

For a list of previous "Chlorine Compound of the Month" features, click here.


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