Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wi ...

mixture with the approximate

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

NaHSO₃. Sodium bisulfite in fact is not a real compound, but a mixture of salts that dissolve in water to give solutions composed of sodium and

bisulfite The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion . Salts containing the ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite disso ...

ions. It appears in form of white or yellowish-white crystals with an odor of

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

. For properties of sodium bisulfite, refer to the table located to the right. Regardless of its ill-defined nature, sodium bisulfite is used in many different industries such a

food additive Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives have been used for centuries as part of an effort to preserve food, for example vinegar (pickling), salt (salt ...

with

E number E numbers ("E" stands for "Europe") are codes for substances used as food additives, including those found naturally in many foods such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

E222 in the food industry, a

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

in the cosmetic industry, and a

decomposer Decomposers are organisms that break down dead or decaying organisms; they carry out decomposition, a process possible by only certain kingdoms, such as fungi. Like herbivores and predators, decomposers are heterotrophic, meaning that they use o ...

of residual hypochlorite used in the bleaching industry.

Synthesis

Sodium bisulfite solutions can be prepared by treating a solution of suitable base, such as

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly caustic base and alkali ...

sodium bicarbonate Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...

with

. :SO₂ + NaOH → NaHSO₃ :SO₂ + NaHCO₃ → NaHSO₃ + CO₂ Attempts to crystallize the product yield

Sodium metabisulfite Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used a ...

(also called sodium disulfite), Na₂S₂O₅. Upon dissolution of the metabisulfite in water, bisulfite is regenerated: :Na₂S₂O₅ + H₂O → 2 Na⁺ + 2 HSO₃⁻ Sodium bisulfite is formed during the Wellman-Lord process.

Uses

Cosmetics

The safety of cosmetic products is constantly in question as the components are always changing or being discovered as a possibly harmful substance. The sulfite components of cosmetic ingredients, such as sodium bisulfite, underwent clinical trials to find out their safety in cosmetic formulations. Sodium bisulfite functions as a

and furthermore as a hair-waiving/straightening agent. As of 1998, sodium bisulfite was used in 58 different cosmetic products including hair conditioners, moisturizers, and hair dyes. In a cosmetic context, the reducing ability of sodium bisulfite is used to prevent discoloration, bleach food starches, and delay spoilage of the product. Since the sulfite molecule was used in so many compounds in the 1990s, the EPA, FDA, and American Conference of Governmental Industrial Hygienists established a working place threshold limit value for sulfur dioxide of 2ppm averaged over 8 hours, and a 3-hour level of 5ppm. Even with this threshold established, the FDA recognized sodium bisulfite as a "generally recognized as safe" compound. A final examination on the carcinogenicity, genotoxicity, oral toxicity, and cellular toxicity on consumed sodium bisulfite was conducted using living subjects such as mice and rats. The International Agency for Research on Cancer concluded that there was inadequate evidence to that that sodium bisulfite was

carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

. Under specific conditions such as acidity and concentration level, sodium bisulfite was able to cause negative alterations to the genome such as catalyzing

transamination Transamination is a chemical reaction that transfers an amino group to a ketoacid to form new amino acids. This pathway is responsible for the deamination of most amino acids. This is one of the major degradation pathways which convert essential ...

, and induce sister-chromatid exchanges suggesting possible

genotoxicity Genotoxicity is the property of chemical agents that damage the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with mutagenicity, all mutagens are genotoxic, but some genotoxic su ...

. In a study using Osbourne-Mendel strain rats, it was concluded that oral toxicity was not significant if the consumed concentration was less than 0.1% (615ppm as SO2). A study done by Servalli, Lear, and Cottree in 1984 found that sodium bisulfite did not produce membrane fusion in

hepatic The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

and

murine The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. Members of this subfamily are called murines. In terms of species richness, this subfamily is larger than all mammal families ex ...

glial cells Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form myel ...

and human

fibroblasts A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells o ...

so there is no oral toxicity. These clinical studies concluded that sodium bisulfite was safe to use in cosmetic formulations.

Food industry

Similar to the cosmetic industry, the European Commission requested the

European Food Safety Authority The European Food Safety Authority (EFSA) is the agency of the European Union (EU) that provides independent scientific advice and communicates on existing and emerging risks associated with the food chain. EFSA was established in February 2002, ...

(EFSA) to review and determine if the use of sulfites as food additives was still safe in light of new scientific technology and information. Since sodium bisulfite is a known sulfonating compound, it underwent the experimentation. Based on clinical experiments using rats and mice, the World Health Organization Expert Committee on Food Additives came to the conclusion that 0-0.7mg of sulfur dioxide equivalent/kg of body weight per day will cause no harm to an individual consuming this compound as a food additive. The genotoxicity and carcinogenicity were examined just as in the cosmetic trials and in both cases, no potential for concern with respect to the sulfites were found. The production of sodium bisulfite used as a food additive can be described by the combination of

gas with aqueous

solution in usual absorber apparatuses. In order to analyze the amount of free sulfites in food as a result of the sulfonation of sodium bisulfite, multiple methods can be used including the Monier-Williams type procedure, HPLC after extraction, and Flow Injection analysis. Overall, the use of sodium bisulfite in the food industry as an additive and antioxidant is safe and beneficial to the lifespan of processed foods.

Textile industry

An antichlor is a substance used to decompose residual

hypochlorite In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ble ...

or chlorine after chlorine-based bleaching, in order to prevent ongoing reactions with, and therefore damage to, the material that has been bleached. Sodium bisulfite is an example of an antichlor. Historically, sodium bisulfite has been used in the textile industry, cosmetic industry, food industry, and more. Antichlors are very useful in the textile industry because bleaching of compounds using chlorine is a standard practice. However, the use of sodium bisulfite in the decomposition of excess hypochlorite can lead to harmful byproducts when it comes into contact with water at the concentrations present for industrial use. Contact with these dangerous byproducts or even strong concentrations of sodium bisulfite can be harmful to the environment and contact with the skin. Strong concentrations of these compounds can contaminate ecosystems, harm animals, and cause contact dermatitis with industrial workers. The concentrations that could result in these outcomes are much stronger than the concentrations discussed in the cosmetic and food industry.

References