Sodium hydroxide

This Product Safety Summary is intended to provide a general overview of the chemical substance in the context of ICCA Global Product Strategy. The information in the Summary is basic information and is not intended to provide emergency response, medical or treatment information. In-depth safety and health information can be found in the (extended) Safety Data Sheet (e)SDS for the chemical substance .

General Statement

Pure sodium hydroxide is a solid at room temperature and is generated from sodium chloride (common salt) by electrolysis. Sodium hydroxide is a hydrophilic alkaline substance (high pH) and therefore it is corrosive and hazardous to human health. It is most commonly found as a liquid, which has a concentration of between 20% and 50 % sodium hydroxide in water and is usually referred to as caustic soda liquor. The substance is used in large amounts in a variety of industries.

Chemical Identity
Name: sodium hydroxide
Synonyms: caustic soda, caustic lye, lye (for water solution of sodium hydroxide)
CAS number: 1310-73-2
Molecular formula: NaOH

Use and Applications

Sodium hydroxide has many different functions and uses. For example, within industry it can be used to adjust the pH, to produce biodiesel from vegetable oils, to clean food processing equipment and bottles, to de-ink water (pulp and paper industry), to dry air, to absorb CO₂ from gases, to extract alumina (aluminium industry), to remove grease and paint from metal, to mercerize cotton (textile industry), to peel leather, to peel vegetables, to make pretzels, to manufacture chemicals (intermediate use), to regenerate resins or to soften water. Consumer uses include paint stripping or drain cleaning.

Physical/Chemical Properties

Pure sodium hydroxide is a solid at room temperature, though it is often sold as a liquid (aqueous solution). The appearance of the substance and some physicochemical properties are mentioned in the table below.

Sodium hydroxide is a strong alkaline substance that dissociates completely in water into the sodium ion (Na⁺) and hydroxide ion (OH^-). The dissolution/dissociation in water is strongly exothermic (releases heat), so a vigorous reaction occurs when sodium hydroxide is added to water. The vapour pressure of the substance is very low and the melting point is high. Sodium hydroxide solutions attack aluminium and its alloys, giving off hydrogen gas. It can be neutralised with acids (e.g. hydrochloric acid) giving the sodium salts of the acids, which are usually pH neutral and non-corrosive.

Human Health Safety Assessment

Sodium hydroxide is a strongly alkaline hydrophilic substance and therefore solid sodium hydroxide is highly corrosive. It reacts with greases and fats, which can lead to irreversible damage to any site of contact with the body (for example skin or eyes). Depending on the concentration, solutions of sodium hydroxide in water are corrosive, irritating or non-irritating and they cause direct local effects at the site of contact with the body.

Because of the corrosive properties of sodium hydroxide, a high uptake via the mouth can be fatal. When a very large part of the skin is exposed to sodium hydroxide, it can also result in death. Sodium hydroxide does not cause skin allergies.

Under normal conditions of handling and use of sodium hydroxide, when exposure is limited to low, non-irritating concentrations, the substance will dissociate into its constituent ions and will not be systemically available in the body. As a consequence, sodium hydroxide will not cause systemic toxicity in any organs, including the reproductive system. Furthermore, sodium hydroxide is not carcinogenic or genotoxic.

Environmental Safety Assessment

The hazard of sodium hydroxide for the environment is caused by the hydroxide ion (pH effect). A high concentration in water will result in toxic effects for aquatic organisms e.g. fish. However, a low concentration in water will not result in effects on aquatic organisms because the sodium hydroxide will be neutralized by other substances present in water (for example dissolved carbon dioxide, organic acids) and thus the pH will not increase.

Because sodium hydroxide is neutralized in the environment, the substance is not persistent and it will not accumulate in organisms or in the food chain. Bioaccumulation will not occur.

Exposure

Consumer

Sodium hydroxide is used in consumer products. It can be used, for example, in floor stripping products, wood stripping products, hair straightening agents, oven cleaners, drain cleaners or other cleaning products. It is also used in very small amounts in food products to adjust pH or as an additive (E524). This use poses no risk to consumers. Many different consumer products containing sodium hydroxide may be available. The instructions on the label of these products should be read and followed carefully to ensure safe use.

Direct skin contact with products or solutions containing a low concentration of sodium hydroxide (< 0.5% in water) is not a concern for human health because, at low concentrations, the substance is not irritating or corrosive. No other adverse effects on human health are expected to occur. Direct contact with products or solutions containing high concentrations of sodium hydroxide (>2% in water) should be prevented, because of the corrosive effects.

Worker

Because sodium hydroxide has many different functions and uses, it is extensively used in the industry and also by other professionals.

As mentioned above in the section on consumer exposure, skin contact for products or solutions with a low sodium hydroxide concentration is not a concern for human health because, at low concentrations, the substance is not irritating or corrosive (<0.5% in water).

The sodium hydroxide which is manufactured and used in industry applications is usually corrosive and therefore automated and closed systems are used to prevent direct contact. In such situations,  exposure to the substance for workers is very low. When exposure to an irritating or corrosive product could occur, appropriate personal protective equipment should be used. Workers should consult the manufacturer’s Safety Data Sheet to obtain specific advice.

Environment

The hazard of sodium hydroxide for the environment is caused by the hydroxide ion (pH effect). Because there is legislation for the pH control of waste water and surface water in many countries, a significant pH increase of the aquatic environment (e.g. a river or a sea) is not expected due to the manufacture or use of sodium hydroxide.  Furthermore it is relatively easy to adapt the pH of waste water (to neutralise sodium hydroxide in the water) and therefore significant effects of sodium hydroxide on the aquatic environment are not expected.

Emissions to air are also not a concern because sodium hydroxide will be rapidly neutralised in air due the presence of carbon dioxide in air.

State Agency Review

The substance was reviewed in 2002 under the OECD (Organisation for Economic Co-operation and Development) high production volume (HPV) chemicals program. This is a global program to evaluate the hazards of chemicals.

In 2007 a European Union Risk Assessment Report was published for sodium hydroxide which was prepared in the context of Regulation 793/93 on the evaluation and control of the risks of existing substances. In 2010 sodium hydroxide has been registered under the European Union REACH Regulation EC/1907/2006 and the substance was found to be safe for the uses identified.

The results of all these 3 regulatory programs are available via internet.

Regulatory Information / Classification and Labelling

The substance is subject to harmonised classification and labelling under the EU Classification Labelling and Packaging (CLP) Regulation EC/1272/2008. The main elements are given hereafter:

Skin corrosion category 1A

H314

Causes severe skin burns and eye damage

The hazard statement “causes severe skin burns and eye damage” is applicable for a concentration in chemical products of 2 % w/w or higher. For concentrations in products between 0.5 and 2 % the following hazard statements are applicable:

- Causes skin irritation (H315) and

- Causes serious eye irritation (H319).

The European industry has decided to classify sodium hydroxide as corrosive to metals in the EU (H290; May be corrosive to metals).

Conclusion

Sodium hydroxide is used in large amounts in industry and consumer products. Due to the alkaline properties sodium hydroxide is corrosive at high concentrations. Direct contacts with these products should be prevented. However, no effects on human health are expected when humans are in contact with non-corrosive and non-irritating concentrations of the substance. The substance is neutralised in the environment and therefore it is not persistent. Furthermore it does not accumulate in organisms. Waste water which contains sodium hydroxide should be neutralised (pH control) before it is discharged to the environment. In this way effects on the aquatic environment (for example organisms living in a river) are prevented. Use of this hazardous substance has shown to be safe by careful use and following provided instructions.