Registration Dossier

Data platform availability banner - registered substances factsheets

Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Environmental fate & pathways

Phototransformation in water

Currently viewing:

Administrative data

Link to relevant study record(s)

Description of key information

Phototransformation in water: 7 -78% degradation after 17 days, under a range of conditions (read-across from HEDP-H).

Key value for chemical safety assessment

Additional information

Several supporting studies indicate some photodegradation of HEDP-H and its salts under a range of environmental conditions.

Photodegradation of HEDP-H in water was examined under varying conditions (Saeger, 1979). 7% Photodegradation in 17 days was observed for the test material without sensitisers, 78%, 70% and 6% degradation in 17 days were observed for the test material in the presence of ferric, cupric and zinc nitrate respectively. Two additional studies indicated some photodegradation of HEDP-H: 2.7% degradation in direct photolysis after 60 days (Gledhill and Feijtel, 1992) and 22% and 27% degradation in direct and indirect photolysis after 17 days (Monsanto, 1980).

Several ranges of photodegradation of HEDP(2-3Na) were observed across varying exposure periods, water depths, water types and varying light levels in a review (Steber and Wierich, 1986a-g). Degradation ranged from 4-57% indicating some photodegradation of HEDP(2-3Na).

The acid, sodium and potassium salts in the HEDP category are freely soluble in water and, therefore, the HEDP anion is fully dissociated from its sodium or potassium cations when in solution. Under any given conditions, the degree of ionisation of the HEDP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was HEDP-H, HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK or another salt of HEDP.


Therefore, when a salt of HEDP is introduced into test media or the environment, the following is present (separately):

  1. HEDP is present as HEDP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the system and not whether HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK salts, HEDP-H or another salt was added.
  2. Disassociated sodium/potassium cations. The amount of sodium/potassium present depends on which salt was added.
  3. Divalent and trivalent cations have much higher stability constants for binding with HEDP than the sodium or potassium ions, so would preferentially replace them. These ions include calcium (Ca2+), magnesium (Mg2+) and iron (Fe3+). Therefore, the presence of these in the environment or in biological fluids or from dietary sources would result in the formation of HEDP-dication (e.g. HEDP-Ca, HEDP-Mg) and HEDP-trication (e.g. HEDP-Fe) complexes in solution, irrespective of the starting substance/test material.

In this context, for the purpose of this assessment, read-across of data within the HEDP Category is considered to be valid.