Chapter 3: Builders and water softeners · Part 2: Phosphonates
HEDP
No badge
The worst fact: it barely breaks down. In one standard test only about a third was removed, and almost none fully broke down, so risk assessors assume no breakdown at all in sewage plants. The industry's own assessment said there may be concern for rivers and river sediment if one low toxicity result is confirmed.
Why brands use it: it locks up metals so oxygen bleach stays stable, and it stops scale.
Take care if: you get it in your eyes. Australia classes the acid as "Harmful if swallowed" and "Causes serious eye damage", and its sodium salts as "Harmful if swallowed" and "Causes serious eye irritation".
Comes from: phosphorous acid reacted with acetic anhydride (or phosphorus trichloride with acetic acid).
Myth check: "Phosphate-free means phosphorus-free": no. Phosphonates contain phosphorus, which is why the EU limits total phosphorus, not just phosphate.
Contaminants: nil.
Fair to say: most is removed in sewage plants by sticking to sludge. It's also used as a bone medicine.
Correct as of November 2026. What the badges mean
Sources
- Safe Work Australia. Hazardous Chemical Information System (HCIS): classifications for each chemical, and for formaldehyde.
- 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.
The full source list is at the end of Chapter 3.