Bleach is the generic name for any chemical product that is usedindustrially ordomestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically to a dilute solution ofsodium hypochlorite, also called "liquid bleach".
Many bleaches have broad-spectrumbactericidal properties, making them useful for disinfecting and sterilizing. They are used inswimming 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 thebleaching of wood pulp. Bleaches also have other minor uses, like removingmildew, killingweeds, and increasing the longevity ofcut flowers.[1]
Bleaches work by reacting with many colored organic compounds, such as natural pigments, and turning them into colorless ones. While most bleaches areoxidizing agents (chemicals that can remove electrons from other molecules), some arereducing 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 containhypochlorite, which releases chlorine. "Bleaching powder" usually refers to a formulation containingcalcium hypochlorite.[citation needed]
Oxidizing bleaching agents that do not contain chlorine are usually based onperoxides, such ashydrogen peroxide,sodium percarbonate, andsodium perborate. These bleaches are called "non-chlorine bleach", "oxygen bleach", or "color-safe bleach".[2]
Reducing bleaches have niche uses, such assulfur dioxide, which is used to bleach wool, either as gas or from solutions ofsodium dithionite,[3] andsodium borohydride.
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 theindigo ofdenim. For the same reason, ingestion of the products, breathing of the fumes, or contact with skin or eyes can cause bodily harm and damage health.
The earliest form of bleaching involved spreading fabrics and cloth out in ableachfield to be whitened by the action of theSun andwater.[4][5] In the 17th century, there was a significant cloth bleaching industry in Western Europe, using alternating alkaline baths (generallylye) and acid baths (such aslactic acid from sour milk, and later dilutedsulfuric acid). The whole process lasted up to six months.[4]
Chlorine-based bleaches, which shortened that process from months to hours, were invented inEurope in the late 18th century. Swedish chemistCarl Wilhelm Scheele discovered chlorine in 1774,[4] and in 1785 Savoyard scientistClaude Berthollet recognized that it could be used to bleach fabrics.[4] Berthollet also discoveredsodium hypochlorite, which became the first commercial bleach, namedEau de Javel ("Javel water") after the borough ofJavel, near Paris, where it was produced.
Scottish chemist and industrialistCharles Tennant proposed in 1798 a solution ofcalcium hypochlorite as an alternative for Javel water, and patented bleaching powder (solidcalcium hypochlorite) in 1799.[4][6] Around 1820, French chemistAntoine Germain Labarraque discovered the disinfecting and deodorizing ability of hypochlorites and was instrumental in popularizing their use for such purpose.[7] His work greatly improved medical practice, public health, and the sanitary conditions in hospitals,slaughterhouses, and all industries dealing with animal products.[8]
Louis Jacques Thénard first producedhydrogen peroxide in 1818 by reactingbarium peroxide withnitric acid.[9] Hydrogen peroxide was first used for bleaching in 1882, but did not become commercially important until after 1930.[10]Sodium perborate as a laundry bleach has been used in Europe since the early twentieth century, and became popular in North America in the 1980s.[11]
Colors of natural organic materials typically arise from organicpigments, such asbeta carotene. Chemical bleaches work in one of two ways:
Sunlight acts as a bleach through a process leading to similar results: high-energyphotons of light, often in theviolet orultraviolet 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 a white and typically very faded blue.[14]
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 ofantibiotics. They irreversiblydenature or destroy manyproteins, including allprions, making them extremely versatile disinfectants.
Hypochlorite bleaches in low concentration were also found to attack bacteria by interfering withheat shock proteins on their walls.[15] According to 2013 Home Hygiene and Health report,[16] 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 a variety of clothing in a home setting.[17]
Most industrial and household bleaches belong to three broad classes:
Chlorine-based bleaches are found in many household "bleach" products, as well as in specialized products for hospitals, public health,water chlorination, and industrial processes.
The grade of chlorine-based bleaches is often expressed aspercent active chlorine. One gram of 100% active chlorine bleach has the same bleaching power as one gram of elementalchlorine.
The most common chlorine-based bleaches are:
Other examples of chlorine-based bleaches, used mostly as disinfectants, aremonochloramine,halazone, andsodium dichloroisocyanurate.[19][failed verification]
Peroxide-based bleaches are characterized by theperoxide chemicalgroup, namely two oxygen atoms connected by asingle bond, (–O–O–). This bond is easily broken, giving rise to very reactive oxygen species, which are the active agents of this type of bleach.
The main products in this class are:
In thefood industry, other oxidizing products likebromates are used asflour bleaching andmaturing agents.
Sodium dithionite (also known as sodium hydrosulfite) is one of the most important reductive bleaching agents. It is a white crystalline powder with a weaksulfurous odor. It can be obtained by reactingsodium bisulfite withzinc.
It is used as such in some industrial dyeing processes to eliminate excess dye, residual oxide, and unintended pigments and forbleaching wood pulp.
Reaction of sodium dithionite withformaldehyde producesRongalite.
Thus is used in bleachingwood pulp,cotton,wool,leather andclay.[25]
Innegative film processing, silver halide grains are associated with couplers which, on development, produce metallic silver and a colored image. The silver is 'bleached' to a soluble form in a solution of ferric EDTA, which is then dissolved in 'fix', a solution of sodium or ammonium thiosulfate. The procedure is the same for paper processing except that the EDTA and thiosulfate are mixed in 'bleachfix'.
Inreversal processing, residualsilver in the emulsion after the first development is reduced to a soluble silver salt using a chemical bleach, most commonlyEDTA. A conventional fixer then dissolves the reduced silver but leaves the unexposed silver halide intact. This unexposed halide is then exposed to light or chemically treated so that a second development produces a positive image. In color andchromogenic 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 ofpotassium 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.[26] 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 μg/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.
Industrial bleaching agents can be sources of concern. For example, the use of elemental chlorine in thebleaching of wood pulp producesorganochlorines andpersistent organic pollutants, includingdioxins. According to an industry group, the use of chlorine dioxide in these processes has reduced the dioxin generation to under-detectable levels.[27] However, the respiratory risk from chlorine and highly toxic chlorinated byproducts still exists.
A European study conducted in 2008 indicated that sodium hypochlorite and organic chemicals (e.g.,surfactants,fragrances) contained in several household cleaning products can react to generate chlorinatedvolatile organic compounds (VOCs).[28] These chlorinated compounds are emitted during cleaning applications, some of which are toxic and probable humancarcinogens. The study showed that indoor air concentrations significantly increase (8–52 times forchloroform and 1–1170 times forcarbon 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 andgel".
The significant increases observed in indoor air concentrations of several chlorinated VOCs (especially carbon tetrachloride and chloroform) indicate that 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,[28][29] this conclusion appears to be hypothetical:
Sodium hypochlorite solution, 3–6%, (common household bleach) is typically diluted for safe use when disinfecting surfaces and when used to treat drinking water.[31][32]
A weak solution of 2% household bleach in warm water is typical for sanitizing smooth surfaces before the brewing of beer or wine.[citation needed]
US government regulations (21 CFR 178 Subpart C) 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: e.g. one teaspoon of bleach in a cup of water, or 21 ml per litre, or1/3 cup of bleach in a gallon of water) is effective against manybacteria and someviruses in homes.[33] Even "scientific-grade", commercially produced disinfection solutions such as Virocidin-X usually have sodium hypochlorite as their soleactive ingredient, though they also containsurfactants (to prevent beading) and fragrances (to conceal the bleach smell).[34]
Seehypochlorous acid for a discussion of the mechanism for disinfectant action.
An oral rinse with a 0.05% dilute solution of household bleach is shown to treatgingivitis.[35]
Color-safe bleach is a solution with hydrogen peroxide as the active ingredient (for stain removal) rather than sodium hypochlorite or chlorine.[36] It also has chemicals[which?] in it that help brighten colors.[37] Though hydrogen peroxide is used for sterilization purposes and water treatment, its ability to disinfect laundry is limited because the concentration of hydrogen peroxide in laundry products is lower than what is used in other applications.[37]
The safety of bleaches depends on the compounds present, and their concentration.[38] Generally speaking, the ingestion of bleaches will cause damage to theesophagus andstomach, possibly leading to death. On contact with the skin or eyes, it causes irritation, drying, and potentially burns. Inhalation of bleach fumes can cause mild irritation of the upper airways.[38]Personal protective equipment should always be used when using bleach.
Bleach should never be mixed withvinegar or other acids, as this will create highly toxicchlorine gas, which can cause severe burns internally and externally.[39][40][41][42] Mixing bleach withammonia similarly producesnitrogen trichloride, which is a potentially explosive substance with a foul, irritating and acrid odor.[39][40][42] Mixing bleach withisopropanol oracetone makeschloroform,[43] while mixing withhydrogen peroxide results in anexothermic and potentially explosive chemical reaction that releasesoxygen.[44]
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Miracle Mineral Supplement (MMS), also promoted as "Master Mineral Solution" or "Chlorine Dioxide Solution" or CDS,[45] to evade restrictions by online retail platforms, is a bleach solution that has been fraudulently promoted as a cure-all since 2006.[46] Its main active ingredient issodium chlorite, which is "activated" with citric acid to form chlorine dioxide. In an attempt to evade health regulations, its inventor, Jim Humble, a formerScientologist, founded theGenesis II Church of Health and Healing, which considers MMS as its sacrament.[47][48]
