Chemical Properties
white crystalline powder with a sulfur smell
Definition
ChEBI: An inorganic sodium salt composed of sodium and disulfite ions in a 2:1 ratio.
Hazard
Toxic by inhalation. Upper respiratory tract
irritant. Questionable carcinogen.
Potential Exposure
Sodium metabisulfite is used as an antioxidant in pharmaceutical preparations and as a preservative in foods. People with asthma have a greater chance of having an allergic reaction with this chemical. Individuals allergic to sodium bisulfite (a food preservative found in some wine, fresh shrimp; packaged foods; and restaurant salads and potatoes) may have a severe reaction when exposed to sodium metabisulfite.
First aid
Move victim to fresh air. Call 911 or emergency medical service. Give artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. Administer oxygen if breathing is difficult. Remove and isolate contaminated clothing and shoes. In case of contact with substance, immediately flush skin or eyes with running water for at least 20 minutes. For minor skin contact, avoid spreading material on unaffected skin. Keep victim warm and quiet. Effects of exposure (inhalation, ingestion, or skin contact) to substance may be delayed. Ensure that medical personnel are aware of the material(s) involved and take precautions to protect themselves. Medical observation is recommended for 24 to 48 hours after breathing overexposure, as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consider administering a drug or other inhalation therapy.
Shipping
UN1759 Corrosive solids, n.o.s., Hazard class: 8; Labels: 8-Corrosive material, Technical Name required. UN2693 Bisulfites, inorganic, aqueous solutions, n.o.s., Hazard class: 8; Labels: 8-Corrosive material.
Incompatibilities
A strong reducing agent. Keep away from oxidizers. Mixtures with water forms a strong corrosive. Contact with acids releases toxic fumes. Heat causes decomposition. Slowly oxidized to the sulfate on exposure to air and moisture. Attacks metals
Production Methods
Sodium metabisulfite is prepared by saturating a solution of sodium
hydroxide with sulfur dioxide and allowing crystallization to occur;
hydrogen is passed through the solution to exclude air. Sodium
metabisulfite may also be prepared by saturating a solution of
sodium carbonate with sulfur dioxide and allowing crystallization
to occur, or by thermally dehydrating sodium bisulfite.
General Description
Sodium metabisulfite (MBS, Sodium disulfite) is an inorganic salt. It is the sodium salt of disulphurous (pyrosulfurous) acid. It is widely used in textile dyeing, photography and paper industry. It is also commonly added to various food products and wines as a preservative.
Flammability and Explosibility
Nonflammable
Pharmaceutical Applications
Sodium metabisulfite is used as an antioxidant in oral, parenteral,
and topical pharmaceutical formulations, at concentrations of
0.01–1.0% w/v, and at a concentration of approximately 27% w/v
in intramuscular injection preparations. Primarily, sodium metabisulfite
is used in acidic preparations; for alkaline preparations,
sodium sulfite is usually preferred. Sodium
metabisulfite also has some antimicrobial activity, which is greatest
at acid pH, and may be used as a preservative in oral preparations
such as syrups.
In the food industry and in wine production, sodium metabisulfite
is similarly used as an antioxidant, antimicrobial preservative,
and antibrowning agent. However, at concentrations above
about 550 ppm it imparts a noticeable flavor to preparations.
Sodium metabisulfite usually contains small amounts of sodium
sulfite and sodium sulfate.
Safety
Sodium metabisulfite is widely used as an antioxidant in oral,
topical, and parenteral pharmaceutical formulations; it is also
widely used in food products.
Although it is extensively used in a variety of preparations,
sodium metabisulfite and other sulfites have been associated with a
number of severe to fatal adverse reactions. These are usually
hypersensitivity-type reactions and include bronchospasm and
anaphylaxis. Allergy to sulfite antioxidants is estimated to occur
in 5–10% of asthmatics, although adverse reactions may also occur
in nonasthmatics with no history of allergy.
Following oral ingestion, sodium metabisulfite is oxidized to
sulfate and is excreted in urine. Ingestion may result in gastric
irritation, owing to the liberation of sulfurous acid, while ingestion
of large amounts of sodium metabisulfite can cause colic, diarrhea,
circulatory disturbances, CNS depression, and death.
In Europe, the acceptable daily intake of sodium metabisulfite
and other sulfites used in foodstuffs has been set at up to 3.5 mg/kg
body-weight, calculated as sulfur dioxide (SO2). The WHO has
similarly also set an acceptable daily intake of sodium metabisulfite,
and other sulfites, at up to 7.0 mg/kg body-weight, calculated as
sulfur dioxide (SO2).
LD50 (rat, IV): 0.12 g/kg
Carcinogenicity
Sodium metabisulfite was genotoxic in
mice in vivo as determined by chromosomal
aberration, micronucleus, and sperm shape
assays. It was not mutagenic in bacterial
assays.
storage
On exposure to air and moisture, sodium metabisulfite is slowly
oxidized to sodium sulfate with disintegration of the crystals.
Addition of strong acids to the solid liberates sulfur dioxide.
In water, sodium metabisulfite is immediately converted to
sodium (Na+) and bisulfite (HSO3-) ions. Aqueous sodium
metabisulfite solutions also decompose in air, especially on heating.
Solutions that are to be sterilized by autoclaving should be filled into
containers in which the air has been replaced with an inert gas, such
as nitrogen. The addition of dextrose to aqueous sodium
metabisulfite solutions results in a decrease in the stability of the
metabisulfite.
The bulk material should be stored in a well-closed container,
protected from light, in a cool, dry place.
Regulatory Status
GRAS listed. Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (epidural;inhalation; IM and IV injections; ophthalmic solutions; oral
preparations; rectal, topical, and vaginal preparations). Included
in nonparenteral and parenteral medicines licensed in the UK.
Included in the Canadian List of Acceptable Non-medicinal
Ingredients.
