Chapter 3: Builders and water softeners · Part 1: Phosphates
Trisodium phosphate (TSP)
- Poison schedule (Australia)
The worst fact: it's strongly alkaline (a 1% solution is pH 11.9). Splashes usually cause slight, passing injury, but some have caused moderate permanent clouding of the cornea, "similar to" caustic soda; in one case the solution was hot. Australia classes it as "Causes severe skin burns and eye damage".
Why brands use it: it breaks down fats and grease, which makes it useful for scouring and cleaning before painting.
Take care if: you get it on skin or in your eyes. The international safety card says to rinse skin for at least 15 minutes. In Australia, solid products whose pH at 10 g per litre is above 11.5 are a Schedule 5 Poison, and pure TSP products are above that line.
Comes from: phosphoric acid neutralised with soda ash and/or caustic soda (caustic soda is needed for the final step).
Myth check: "TSP is natural, so it's gentle": no. It's made industrially and it's corrosive.
Contaminants: nil.
Fair to say: sodium phosphates are approved food additives. Australia's regulator rates household use as "not unreasonable" risk if you keep it off skin and out of eyes.
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).
- ILO/WHO International Chemical Safety Card: trisodium phosphate.
- HSDB (US National Library of Medicine), via PubChem: production, pH and impurity data for each chemical.
The full source list is at the end of Chapter 3.