Chapter 3: Builders and water softeners · Part 3: Zeolites and silicates
Sodium silicate and disodium disilicate
- Contaminant risk
The worst fact: a 68-year-old woman who deliberately drank 500 mL of an egg-preserving water-glass solution (sodium metasilicate, per the original report) died within about an hour. She vomited and breathed it in, and it turned solid in her lungs. Australia classes sodium silicate and disodium disilicate as "Causes severe skin burns and eye damage" and "May cause respiratory irritation".
Why brands use it: it softens water, buffers the pH and protects machine parts from corrosion.
Take care if: you have children, or for your eyes. Silicates are "alkaline salts" in Australia's Poisons Standard. A solid product is a Schedule 5 Poison if a 10 g per litre solution is above pH 11.5. Solid home dishwasher products are tested at 500 g per litre: above pH 11.5 they're Schedule 5, and above pH 12.5 they're banned. How alkaline a silicate is depends on its type: from about pH 10 up to 13. The most alkaline, sodium metasilicate, is in Chapter 10.
Comes from: quartz sand fused with soda ash at 1,100 to 1,500°C.
Myth check: "Breathing the powder is a big risk": Australia's regulator says consumer silicate powders are sieved so the particles are too big to breathe in.
Contaminants: arsenic and lead. In typical silicate solutions, arsenic is below the 1 ppm detection limit and lead is 0.17 to 0.60 ppm. They're unlikely to matter in a well-made product, but it's a factor you can't see on the label.
Fair to say: once diluted, silica is natural in water: diatoms (single-celled algae) use it to build their shells. The danger is the alkalinity.
Correct as of November 2026. What the badges mean
Sources
- Australian Government. Poisons Standard October 2026 (SUSMP), F2026L01327: alkaline salts; trisodium nitrilotriacetate.
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for formaldehyde.
- AICIS. Evaluation statement EVA00169: EDTA and its salts (2025). IMAP assessments: trisodium phosphate (2016); etidronic acids (2013); soluble silicates (2016); nitrilotriacetic acid and salts (2017).
- HERA. Risk assessments: STPP (2003) and STPP eutrophication note (2003); phosphonates (2004); zeolite A (2004); soluble silicates (2005); polycarboxylates parts I and II (2014).
- HSDB (US National Library of Medicine), via PubChem: production, pH and impurity data for each chemical.
- Sigrist T, Flury K. Death by peroral ingestion of soluble glass (sodium silicate). Z Rechtsmed 1985;94:245-250.
The full source list is at the end of Chapter 3.