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All About Chlorine Bleach

We rely on chlorine bleach for effective sanitization and disinfection, but do you know exactly what it is and where it’s used?

What exactly is chlorine bleach?

There are several types of chlorine bleach, the most commonly known one being liquid sodium hypochlorite (NaOCl). Other types of chlorine-based bleaching and disinfecting compounds include calcium hypochlorite (Ca[ClO]2) and sodium dichloroisocyanurate (“dichlor” or NaDCC), among others.

What is chlorine bleach used for?

Chlorine bleach has been used for generations to disinfect all kinds of environmental surfaces, help keep drinking water germ-free, and make swimming pools healthy. It can be used to whiten products including laundry, paper, soap, straw, and cotton.

Because it is one of the world’s most common and affordable disinfectants, bleach plays a key role in public health. Using bleach solutions on frequently touched surfaces, such as door knobs, and on food contact surfaces, can help prevent the spread of diseases by destroying pathogens. Bleach is commonly used to disinfect surfaces in child care and adult care centers, and in hospitals where there is an increased risk of spreading infectious diseases and antimicrobial resistant “superbugs.” After a natural disaster or during an emergency, chlorine bleach can be used to disinfect contaminated water sources and to help control the growth of mold after flooding.

A deeper dive into chlorine bleach

More about household bleach

The type of household bleach consumers are most familiar with is liquid sodium hypochlorite. Household bleaches are sold in supermarkets and other stores in a bleach solution of 6% sodium hypochlorite mixed with water. Sodium hypochlorite is produced by chemically reacting chlorine gas with sodium hydroxide (NaOH) solution. Over time, the sodium hypochlorite compound breaks down to salt and water. Therefore, older bottles of chlorine bleach may no longer contain the 6% concentration of sodium hypochlorite they contained when purchased.

Calcium hypochlorite is another bleaching compound often referred to as bleaching powder or granular bleach. It is a dry solid sold in granules or compacted disks. Calcium hypochlorite is made by reacting chlorine gas (Cl2) with lime (Ca(OH)2).

How does chlorine bleach disinfect?

The powerful disinfectant properties of chlorine bleach are actually mainly a result of the formation of hypochlorous acid, a weak acid that forms when liquid or granular bleach is added to water. Hypochlorous acid is electrically neutral and can easily make contact with and pass through the cell walls/membranes of bacteria or shell casings (capsids) of viruses, such as Salmonella or norovirus pathogens. Once inside the pathogen, the hypochlorous acid chemically interacts with proteins, causing their intricate structure to unfold, which disrupts their functions and inactivates the pathogen.

Effective bleach disinfection depends upon adequate contact time with the pathogen. The recommended contact time is a function of the temperature, the bleach solution strength, and the specific pathogen. Certain pathogens require longer contact times than others. The Water Quality & Health Council provides free informational disinfection posters for a variety of surfaces and pathogens.

To learn more about how bleach disinfects, check out this video.

Is bleach harmful to the environment?

When bleach is used according to the manufacturers’ label instructions, it does not pose a risk to the environment. As chlorine bleach reacts with germs and other organic matter, it degrades into mostly salty water. Any unreacted bleach will be degraded upon contact with organic matter in the wastewater collection system or during municipal wastewater treatment.

Of course, using chlorine bleach in ways it is not supposed to be used  can pose a risk to the environment. Therefore, it is always advised to use bleach according to the manufacturer’s label instructions.

 

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