Aluminium Sulphate (E 520) – Uses and Safety
Aluminium sulphate is an inorganic aluminium compound widely used in water treatment, the food industry, and medicine as an astringent and coagulant.
Things worth knowing about "Aluminium sulphate"
Aluminium sulphate is an inorganic aluminium compound widely used in water treatment, the food industry, and medicine as an astringent and coagulant.
What is Aluminium Sulphate?
Aluminium sulphate (chemical formula: Al2(SO4)3) is an inorganic salt composed of aluminium and sulphuric acid. It typically appears as a white or colourless crystalline powder and dissolves readily in water. Its aqueous solution is acidic, as aluminium ions react with water to release hydrogen ions.
The compound is known under several names, including alum in certain hydrated forms. In the European Union food industry, aluminium sulphate is authorised as a food additive under the designation E 520.
Occurrence and Production
Aluminium sulphate occurs naturally in small amounts in certain minerals and acidic soils. Industrially, it is produced by reacting aluminium hydroxide or aluminium oxide with sulphuric acid. Depending on the water content, a distinction is made between anhydrous aluminium sulphate and various hydrated forms (e.g., aluminium sulphate octadecahydrate).
Areas of Application
Water Treatment
The most important industrial application of aluminium sulphate is in drinking water and wastewater treatment. Acting as a coagulant, it binds fine suspended particles, colloids, and organic impurities in water. The aluminium hydroxide flocs formed settle out and can be easily filtered. This process is referred to as flocculation.
Food Industry (E 520)
In food processing, aluminium sulphate is used as a firming agent and acidity regulator. It is employed in the production of pickled vegetables (e.g., cucumbers), baking powders, and certain flour-based products. The European Food Safety Authority (EFSA) has assessed its use under defined maximum levels. Due to concerns regarding total aluminium intake, permissible limits have been tightened in recent years.
Medicine and Pharmacy
In medical applications, aluminium sulphate is primarily used as an astringent. It causes tissue contraction, reduces excess secretions, and can stop minor bleeding (e.g., after shaving or small cuts). Well-known products include so-called styptic pencils, which contain aluminium sulphate or related aluminium compounds. It is also used in certain antiperspirants and as an adjuvant in some vaccines.
Other Industrial Applications
Outside medicine and food, aluminium sulphate is used in paper manufacturing, the textile industry (as a mordant in dyeing), cosmetics, and horticulture (for soil acidification to support acid-loving plants such as rhododendrons).
Health Assessment and Safety
The health assessment of aluminium sulphate is closely linked to the broader question of aluminium exposure in the human body. Aluminium is absorbed in small amounts through food, drinking water, cosmetics, and medications. The majority is excreted via the kidneys.
In healthy adults, moderate aluminium intake within the tolerable weekly intake (TWI) established by EFSA (1 mg per kg body weight per week) is considered safe. However, elevated aluminium exposure may be problematic for the following groups:
- Individuals with impaired kidney function
- Premature infants and babies
- Persons with high occupational aluminium exposure
Chronically excessive aluminium intake has been discussed in the scientific literature in relation to neurological changes. However, a definitive causal link, for example to Alzheimer's disease, has not been conclusively established.
Interactions and Notes
Aluminium sulphate can interfere with the absorption of certain minerals, including phosphate, fluoride, and iron, in the gastrointestinal tract. When taken alongside certain medications, particularly antibiotics (tetracyclines, fluoroquinolones) or thyroid hormones, aluminium may reduce their absorption. Patients should take such medications at a different time.
References
- European Food Safety Authority (EFSA): Reassessment of aluminium sulphates (E 520-523) and sodium aluminium silicate (E 554) as food additives. EFSA Journal, 2018.
- World Health Organization (WHO): Aluminium in Drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality. WHO, Geneva, 2010.
- Bundesinstitut für Risikobewertung (BfR): Aluminium-containing food additives – Statement No. 008/2019. Berlin, 2019.
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