Chlorine Bleach

Bleaches work by oxidising substances. They sanitise and remove stains by breaking bonds within a molecule. This produces smaller fragments which do not absorb light in the visible light spectrum (with respect to human sight), making the broken fragments colourless. [1]

Image source: Compound Interest

What is chlorine bleach?

Chlorine bleach is sodium hypochlorite (NaOCl) diluted in water to produce a certain concentration eg 1%, 4.5% etc. It is standard household bleach sold in the laundry aisle of the supermarket.
Chlorine bleach is unstable and reactive, which is why it has a shelf life, eventually turning into salt water.

How does chlorine bleach sanitise?

Sodium hypochlorite is effective against bacteria, viruses and fungi (mould) [2], sanitising the same way as chlorine does. [3] It is one of the most effective sanitisers, it kills almost every pathogen there is, including influenza virus, ebola [4], but unfortunately not tuberculosis.

Chlorine kills pathogens by breaking the chemical bonds within the organism, disrupting metabolism and protein synthesis. When enzymes come into contact with chlorine, the hydrogens in the molecule are replaced by chlorine. This causes the entire molecule to change shape or collapse. When enzymes do not function properly, the organism will die. [3]

When chlorine is added to water, it reacts with organic matter and other impurities in the water, forming chloride salts, and with organic material in water to form chlorinated organic chemicals. The amount of chlorine needed for disinfection will depend on the concentrations of these impurities, concentration of available chlorine, pH and temperature of the water and contact time. [5] [6] [7] [8]

The most effective, easy and inexpensive sanitisation options are chlorine bleach and 90/95°C sanitise options. Chlorine bleach is bactericidal (kills bacteria) at low concentrations, and both of these methods oxidise ammonia.

Advantages

  • Broad antimicrobial spectrum
  • Rapid bactericidal action
  • Solubility
  • Easy to use
  • Readily available
  • Inexpensive
  • Does not bio accumulate in the environment
  • Does not contribute to bacterial resistance
  • Wide range of applications
  • Colourless, non flammable, non staining
  • Effective
  • Safe to use

Disadvantages

  • Can irritate skin, mucous membranes and airways
  • Can not be mixed with acids or ammonia
  • Will permanently remove colour from natural fabrics if used at a concentration which is too high
  • Can require repeated treatment to sufficiently kill mould, as hyphae feet hook into porous surfaces (not an issue with textiles which can be submerged)

Applications

Chlorine sanitisation is used in many industries and applications.

  • Drinking water sanitisation [5] [8] [12]
  • Swimming pool water sanitisation
  • Hospital and medical equipment sanitisation [4] [6] [7]
  • Pharmaceuticals
  • Textile production
  • Polyurethane production (including PUL used to make modern cloth nappies) [13]
  • Food industry [6]
  • Household bathroom mould removal products [2]
  • Eczema and skin condition treatment [10]

Sodium hypochlorite is the active sanitising agent in Milton, which is used to sanitise baby bottles.

Health and Environmental Impact

Because of its mode of action, relatively short life span, and formation into salt water, sodium hypochlorite doesn’t bio accumulate. Small amounts are septic tank system safe.
Benzalkonium Chloride which is the active ingredient in Laundry Sanitisers eg Canesten or Dettol, does not readily degrade and as a result can contribute to bacterial resistance. [9]

Sodium hypochlorite is recommended to treat skin conditions like eczema.
People with eczema, especially atopic dermatitis, tend to have very dry skin in general. This is because the disease causes defects in the skin barrier. Skin prevents irritants, bacteria/viruses, and allergens from getting into our bodies and moisture from getting out. Chlorine bleach diluted in bath water decreases inflammation and the amount of bacteria on the skin, which can lead to skin infections. [10]

Safe use

Do not mix chlorine bleach with acids, or ammonia. When sodium hypochlorite and ammonia are combined they form chloramine gas which if inhaled is dangerous. But using chlorine bleach to oxidise ammonia from cloth nappies is not dangerous and won’t cause this gas, as the bleach is diluted, the nappies are washed before sanitisation which means and the ammonia in the fabric is not a concentrated liquid.

Chlorine can irritate skin and mucous membranes, use gloves and ensure there is adequate ventilation, to prevent exposing skin or inhaling concentrated bleach. If the user has a specific allergy to bleach (eg it triggers asthma) don’t use it. Ensure it is thoroughly washed out of fabrics before use again.
While chlorine bleach can be used safely on dyed/coloured fabrics to remove stains when it has been diluted to a low enough, colourfast concentration, it will irreversibly removed colour from natural fabrics such as cotton if used at a concentration which is too high.

History of Napisan

In the 1970s and 80s, the active ingredient in Napisan was potassium monopersulfate (KHSO5) which oxidises sodium chloride to sodium hypochlorite (chlorine bleach), but the formulation was changed and the sodium hypchlorite was replaced with sodium percarbonate (oxygen bleach). [11]

[1] Benckiser, R. Chemistry in Your Cupboard: Vanish- Learn Chemistry
[2] Occurrence of household mold and efficacy of sodium hypochlorite disinfectant
[3] Lenntech
[4] Interim Infection Prevention and Control Guidance for Care of Patients with Suspected or Confirmed Filovirus Haemorrhagic Fever in Health-Care Settings, with Focus on Ebola
[5] Australian Government Department of Health
[6] Mechanisms of Actions of Sodium Hypochlorite in Cleaning and Disinfection Processes
[7] World Health Organisation Infection Prevention and Control of Epidemic- and Pandemic-Prone Acute Respiratory Infections in Health Care
[8] World Health Organization Water Sanitisation Guidelines
[9] Effect of subinhibitory concentrations of benzalkonium chloride on the competitiveness of Pseudomonas aeruginosa grown in continuous culture
[10] National Eczema Association
[11] H. Gaya et al, J. Hyg., Camb. 1979, 82,463
[12] World Health Organization Water Sanitation
[13] American Chemistry Council

Author A. Michailov