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CAS Number: 1330-43-4 (anhydrous); 1303-96-4 (decahydrate, the common form)
Synonyms: Borax, sodium tetraborate decahydrate, sodium borate, E285, disodium tetraborate, sodium pyroborate, borax decahydrate (Na₂B₄O₇·10H₂O), sodium biborate, sodium tetraborate pentahydrate (Na₂B₄O₇·5H₂O), fused borax (anhydrous)
Physical Properties: White, odorless crystalline powder or hard, colorless to white monoclinic crystals (decahydrate form). Soluble in water (approx. 5.8 g/100 mL at 20°C for decahydrate; more soluble in hot water). Insoluble in ethanol. Molecular weight 381.37 g/mol (decahydrate); 201.22 g/mol (anhydrous). Melting point 75°C (decahydrate loses water and melts in its own water of crystallization); anhydrous borax melts at 741°C. Density 1.73 g/cm³ (decahydrate); 2.37 g/cm³ (anhydrous). pH of 1% solution is approximately 9.2 (alkaline due to hydrolysis to boric acid and sodium hydroxide). Stable under normal storage; effloresces slightly in dry air (decahydrate loses water to form lower hydrates). When heated, expands and intumesces (puffs up) to form a porous glassy mass (borax bead used in analytical chemistry).
Applications: Formerly used as food preservative (E285) for caviar, fish roe, margarine, and cheese (now banned in most countries). Household uses (laundry booster, cleaning agent, water softener, stain remover, multi-purpose cleaner). Industrial uses (flux for welding and soldering, component of enamels and ceramic glazes, buffer in chemical laboratories, corrosion inhibitor in antifreeze, flame retardant in textiles, wood preservative, adhesive ingredient for casein glues, crosslinking agent for polyvinyl alcohol (PVA) slime and putty). Agriculture (boron micronutrient fertilizer, insecticide against ants and cockroaches, fungicide). Cosmetics (buffer and emulsifier in creams, lotions, bath salts, and shampoos). Metallurgy (extraction of metals from ores, flux in gold and silver refining). Glass and ceramics (manufacture of borosilicate glass, fiberglass, and vitreous enamels). Analytical chemistry (buffer in electrophoresis, component of tetraborate buffers for DNA/RNA separation).
Description:
Sodium tetraborate, commonly known as borax (E285), is a naturally occurring boron-containing mineral that was historically used as a food preservative. Like boric acid (E284), borax was employed primarily to preserve caviar, fish roe, margarine, butter, and some cheese products. When dissolved in water, borax hydrolyzes to form boric acid and sodium hydroxide according to the reaction Na₂B₄O₇ + 7H₂O → 4H₃BO₃ + 2NaOH, and it is the released boric acid that provides the antimicrobial effect. Boric acid acts by penetrating microbial cell membranes, inhibiting dehydrogenase enzymes, disrupting nucleic acid synthesis, and interfering with cell wall synthesis. However, as with boric acid, the antimicrobial activity of borax is relatively weak, requiring concentrations of 0.5 to 4.0 percent for effective preservation, which are far higher than those of modern preservatives.
The use of borax as a food additive has been banned in virtually all developed countries due to serious reproductive and developmental toxicity. The European Union has prohibited E285 in food entirely, and the United States FDA does not permit borax as a food additive. JECFA has withdrawn the acceptable daily intake for borax and borates, as these substances are no longer considered acceptable for food use. Borax shares the same toxicological profile as boric acid because it converts to boric acid in the body. The primary concerns are teratogenicity (causing fetal malformations in animal studies including skeletal abnormalities, low birth weight, and cardiovascular defects at doses only slightly above estimated dietary intake), testicular toxicity (reduced sperm count, testicular atrophy, and impaired fertility in males), and developmental neurotoxicity. Acute poisoning from ingestion of borax causes nausea, vomiting, diarrhea, abdominal pain, erythematous rash ("boiled lobster" appearance), headache, lethargy, and in severe cases, seizures, kidney failure, metabolic acidosis, and death. The estimated lethal dose in adults is 15 to 20 grams of boric acid equivalent, but severe poisoning in infants has occurred with doses as low as 5 grams.
The historical use of borax in caviar preservation is particularly noteworthy. Before modern refrigeration and approved preservatives (such as E239 hexamethylene tetramine, now also banned, or E200 sorbic acid), caviar was often preserved with borax to extend its shelf life during long-distance transport from the Caspian Sea to European and Russian markets. The practice persisted in some regions until the late 20th century, but it has now been almost entirely eliminated due to both toxicity concerns and the availability of safer alternatives. Today, even high-end caviar is preserved using low-temperature storage, vacuum packaging, and minimal amounts of salt, rather than boron compounds.
Despite its ban in food, borax remains widely used in household, industrial, and cosmetic applications. In laundry and cleaning, it functions as a water softener by binding calcium and magnesium ions (which interfere with detergent action), as a buffering agent to maintain alkaline pH (which enhances grease removal), and as a mild bleach through the formation of hydrogen peroxide in solution. In welding and metallurgy, borax is used as a flux to remove metal oxides and prevent reoxidation during heating, allowing clean metal surfaces to join. In ceramics and glass manufacturing, it lowers the melting point of silica, promotes glass formation, and improves thermal shock resistance (borosilicate glass). In cosmetics, borax is used as an emulsifier and buffering agent in creams, lotions, bath salts, and shampoos, typically at concentrations below 3 percent, though its use in leave-on products has declined due to safety concerns. Interestingly, borax is a key ingredient in "slime" and putty made from polyvinyl alcohol (PVA) glue, where borate ions crosslink the PVA polymer chains, transforming a liquid glue into a viscoelastic, stretchy solid. This reaction is a classic demonstration of polymer crosslinking used in educational chemistry activities. Borax is also used as a boron micronutrient fertilizer in agriculture for boron-deficient soils, particularly for crops such as apples, broccoli, cauliflower, and sugar beets. In this context, the application rates are carefully controlled because excess boron is toxic to plants. Overall, the food use of E285 is obsolete and prohibited in modern food regulation, but borax continues to have legitimate and valuable applications outside the food industry.
SAFETY INFORMATION ABOUT E285 – SODIUM TETRABORATE: BORAX
First aid measures:
Description of first aid measures:
General advice:
Consult a physician.
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
If inhaled:
If breathed in, move person into fresh air.
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately.
Wash off with soap and plenty of water.
Consult a physician.
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
If swallowed:
Do NOT induce vomiting.
Never give anything by mouth to an unconscious person.
Rinse mouth with water.
Consult a physician.
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment.
Avoid breathing vapours, mist or gas.
Evacuate personnel to safe areas.
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste.
Keep in suitable, closed containers for disposal.
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place.
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles.
Faceshield (8-inch minimum).
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
Skin protection:
Handle with gloves.
Gloves must be inspected prior to use.
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product.
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices.
Wash and dry hands.
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls.
If the respirator is the sole means of protection, use a full-face supplied air respirator.
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions.
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company.
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product
