Bleach is the generic name for any chemical product which is used industrially and domestically to remove color from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers, specifically, to a dilute solution of sodium hypochlorite, also called "liquid bleach".
Many bleaches have broad spectrum bactericidal properties, making them useful for disinfecting and sterilizing and are used in swimming pool sanitation to control bacteria, viruses, and algae and in many places where sterile conditions are required. They are also used in many industrial processes, notably in the bleaching of wood pulp. Bleaches also have other minor uses like removing mildew, killing weeds, and increasing the longevity of cut flowers.
Bleaches work by reacting with many colored organic compounds, such as natural pigments, and turning them into colorless ones. While most bleaches are oxidizing agents (chemicals that can remove electrons from other molecules), some are reducing agents (that donate electrons).
Chlorine, a powerful oxidizer, is the active agent in many household bleaches. Since pure chlorine is a toxic corrosive gas, these products usually contain hypochlorite, which releases chlorine when needed. "Bleaching powder" usually means a formulation containing calcium hypochlorite.
Bleaches generally react with many other organic substances besides the intended colored pigments, so they can weaken or damage natural materials like fibers, cloth, and leather, and intentionally applied dyes such as the indigo of denim. For the same reason, ingestion of the products, breathing of the fumes, or contact with skin or eyes can cause health damage.
Early method of bleaching cotton and linen goods on lawns
The earliest form of bleaching involved spreading fabrics and cloth out in a bleachfield to be whitened by the action of the sun and water. In the 17th century, there was a significant cloth bleaching industry in Western Europe, using alternating alkaline baths (generally lye) and acid baths (such as lactic acid from sour milk, and later diluted sulfuric acid). The whole process lasted up to six months.
Chlorine-based bleaches, which shortened that process from months to hours, were invented in Europe in the late 18th century. Swedish chemist Carl Wilhelm Scheele discovered chlorine in 1774, and in 1785 French scientist Claude Berthollet recognized that it could be used to bleach fabrics. Berthollet also discovered sodium hypochlorite, which became the first commercial bleach, named Eau de Javel ("Javel water") after the borough in Paris where it was produced. Scottish chemist and industrialist Charles Tennant proposed in 1798 a solution of calcium hypochlorite as an alternative for Javel water, and patented bleaching powder (solid calcium hypochlorite) in 1799. Around 1820, French chemist Antoine Germain Labarraque discovered the disinfecting and deodorizing ability of hypochlorites, and was instrumental in popularizing their use for such purpose. His work greatly improved medical practice, public health, and the sanitary conditions in hospitals, slaughterhouses, and all industries dealing with animal products.
Colors of natural organic materials typically arise from organic pigments, such as beta carotene. Chemical bleaches work in one of two ways:
An oxidizing bleach works by breaking the chemical bonds that make up the chromophore. This changes the molecule into a different substance that either does not contain a chromophore, or contains a chromophore that does not absorb visible light. This is the mechanism of bleaches based on chlorine but also of oxygen-anions which react through initial nucleophilic attack.
A reducing bleach works by converting double bonds in the chromophore into single bonds. This eliminates the ability of the chromophore to absorb visible light. This is the mechanism of bleaches based on sulfur dioxide.
Sunlight acts as a bleach through a process leading to similar results: high energy photons of light, often in the violet or ultraviolet range, can disrupt the bonds in the chromophore, rendering the resulting substance colorless. Extended exposure often leads to massive discoloration usually reducing the colors to white and typically very faded blue.
The broad-spectrum effectiveness of most bleaches is due to their general chemical reactivity against organic compounds, rather than the selective inhibitory or toxic actions of antibiotics. They irreversibly denature or destroy many proteins, making them extremely versatile disinfectants.
Hypochlorite bleaches in low concentration were also found to attack bacteria by interfering with heat shock proteins on their walls. According to 2013 Home Hygiene and Health report, using bleach, whether chlorine- or peroxide-based, significantly increases germicidal efficiency of laundry even at low temperatures (30-40 degrees Celsius), which makes it possible to eliminate viruses, bacteria and fungi from variety of clothing in home setting.
Classes of bleaches
Most industrial and household bleaches belong to three broad classes:
Bleaching powder (formerly known as "chlorinated lime"), usually a mixture of calcium hypochlorite , calcium hydroxide (slaked lime, ), and calcium chloride in variable amounts. Sold as a white powder or in tablets, is used in many of the same applications as sodium hypochlorite, but is more stable and contains more available chlorine.
Hydrogen peroxide itself . It is used, for example, to bleach wood pulp and hair or to prepare other bleaching agents like the perborates, percarbonates, peracids, etc.
Sodium percarbonate , an adduct of hydrogen peroxide and sodium carbonate ("soda ash" or "washing soda", ). Dissolved in water, it yields a solution of the two products, that combines the degreasing action of the carbonate with the bleaching action of the peroxide.
In Reversal processing, residual silver in the emulsion after the first development is reduced to a soluble silver salt using a chemical bleach, most commonly EDTA. A conventional fixer then dissolves the reduced silver but leaving the unexposed silver halide intact. This unexposed halide is then exposed to light or is chemically treated so that a second development produces a positive image. In colour and chromogenic film, this also generates a dye image in proportion to the silver.
Photographic bleaches are also used in black-and-white photography to selectively reduce silver to reduce silver density in negatives or prints. In such cases the bleach composition is typically an acid solution of potassium dichromate.
A Risk Assessment Report (RAR) conducted by the European Union on sodium hypochlorite conducted under Regulation EEC 793/93 concluded that this substance is safe for the environment in all its current, normal uses. This is due to its high reactivity and instability. The disappearance of hypochlorite is practically immediate in the natural aquatic environment, reaching in a short time concentration as low as 10-22 ?g/L or less in all emission scenarios. In addition, it was found that while volatile chlorine species may be relevant in some indoor scenarios, they have a negligible impact in open environmental conditions. Further, the role of hypochlorite pollution is assumed as negligible in soils.
A recent European study indicated that sodium hypochlorite and organic chemicals (e.g., surfactants, fragrances) contained in several household cleaning products can react to generate chlorinated volatile organic compounds (VOCs). These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable human carcinogens. The study showed that indoor air concentrations significantly increase (8-52 times for chloroform and 1-1170 times for carbon tetrachloride, respectively, above baseline quantities in the household) during the use of bleach-containing products. The increase in chlorinated volatile organic compound concentrations was the lowest for plain bleach and the highest for the products in the form of "thick liquid and gel." The significant increases observed in indoor air concentrations of several chlorinated VOCs (especially carbon tetrachloride and chloroform) indicate that the bleach use may be a source that could be important in terms of inhalation exposure to these compounds. While the authors suggested that using these cleaning products may significantly increase the cancer risk, this conclusion appears to be hypothetical:
The highest level cited for a concentration of carbon tetrachloride (seemingly of highest concern) is 459 micrograms per cubic meter, translating to 0.073 ppm (part per million), or 73 ppb (part per billion). The OSHA-allowable time-weighted average concentration over an eight-hour period is 10 ppm, almost 140 times higher;
The OSHA highest allowable peak concentration (5-minute exposure for five minutes in a 4-hour period) is 200 ppm, twice as high as the reported highest peak level (from the headspace of a bottle of a sample of bleach plus detergent).
Sodium hypochlorite solution, 3-6%, (common household bleach) is typically diluted for safe use when disinfecting surfaces and when used to treat drinking water.
A weak solution of 2% household bleach in warm water is typical for sanitizing smooth surfaces prior to the brewing of beer or wine.
US Government regulations (21 CFR Part 178) allow food processing equipment and food contact surfaces to be sanitized with solutions containing bleach, provided that the solution is allowed to drain adequately before contact with food, and that the solutions do not exceed 200 parts per million (ppm) available chlorine (for example, one tablespoon of typical household bleach containing 5.25% sodium hypochlorite, per gallon of water).
A 1-in-47 dilution of household bleach with water (1 part bleach to 47 parts water) is effective against many bacteria and some viruses in homes. Even "scientific-grade", commercially produced disinfection solutions such as Virocidin-X usually have sodium hypochlorite as their sole active ingredient, though they also contain surfactants (to prevent beading) and fragrances (to conceal the bleach smell).
An oral rinse with a 0.05% dilute solution of household bleach is shown to treat gingivitis.
Diluted sodium hypochlorite at a rate of 2000-1 (0.05% concentration) may represent an efficacious, safe and affordable antimicrobial agent in the prevention and treatment of periodontal disease.
Color safe bleach
Color safe bleach is a chemical that uses hydrogen peroxide as the active ingredient (to help remove stains) rather than sodium hypochlorite or chlorine. It also has chemicals in it that help brighten colors. Hydrogen peroxide is also used for sterilization purposes and water treatment, but its disinfectant capabilities may be limited due to the concentration in the colorsafe bleach solution as compared to other applications.
The safety of bleaches depends on the compounds present, and their concentration. Generally speaking, the ingestion of bleaches will cause damage to the esophagus and stomach, possibly leading to death. On contact with the skin or eyes, it causes irritation, drying, and potentially burns. Inhalation of bleach fumes can damage the lungs.Personal protective equipment should always be used when using bleach. Bleach should never be mixed with vinegar or other acids as this will create highly toxic chlorine gas and can cause severe burns internally and externally. Mixing bleach with ammonia similarly produces toxic chloramine gas, which can burn the lungs. Mixing bleach with hydrogen peroxide results in an exothermic chemical reaction that releases oxygen, and may cause the contents to splatter and cause skin and eye injury. Heating bleach and boiling it may produce chlorates, a strong oxidizer which may lead to a fire or explosion.
False claims as a cure
Miracle Mineral Supplement (MMS), also promoted as "Master Mineral Solution" or "Chlorine Dioxide Solution" or CDS, to evade restrictions by online retail platforms, is a bleach solution that has been fraudulently promoted as a cure-all since 2006. Its main active ingredient is sodium chlorite, which is "activated" with citric acid to form chlorine dioxide. In an attempt to evade health regulations, its inventor, former Scientologist, Jim Humble, formed the Genesis II Church of Health and Healing, a fake religion whose "sacrament" is MMS.
During the COVID-19 pandemic advocates of MMS, such as QAnon proponent Jordan Sather and Mark Grenon, who are affiliated with the Genesis II Church, began to suggest this would treat COVID-19. Several sources interpreted remarks by U.S. President Trump, in an April 23, 2020 briefing, as promoting this claim, leading the CDC, scientists, and bleach companies to re-state that bleach is harmful to humans and should not be ingested or injected. MSN News quoted Professor Rob Chilcott, a toxicology expert from the University of Hertfordshire, that there is no scientific evidence that injected bleach or disinfectants will affect viral particles, but that injecting bleach would "likely result in significant, irreversible harm and probably a very unpleasant death."
^Phillips, H. (2008). "The Bleaching of Wool with Sulphur Dioxide and with Solutions of Sulphites". Journal of the Society of Dyers and Colourists. 54 (11): 503-512. doi:10.1111/j.1478-4408.1938.tb01992.x.
^Herman Harry Szmant (1989). Organic building blocks of the chemical industry. John Wiley and Sons. p. 113. ISBN978-0-471-85545-3.
^European Union Risk Assessment Report. 2007. Sodium Hypochlorite (CAS No: 7681-52-9; EINECS No: 231-668-3): Final report, November 2007 (Final Approved Version); see Risk Assessment Report on Sodium Hypochlorite, Scientific Committee on Health and Environmental Risks, 12 March 2008.
^Dvorak, Glenda (February 2005). "Disinfection"(PDF). Center for Food Security and Public Health. Ames, IA: Center for Food Security and Public Health, Iowa State University. p. 12. Archived from the original(PDF) on 19 June 2010. Retrieved 2011.