Potassium salts of [hexane-1,6-diylbis[nitrilobis(methylene)]]tetrakisphosphonic acid (4-7 K:1)

Endpoint summary

Description of key information

Short-term marine toxicity data are available with the registered substance for fish and invertebrates. A 96 h L(E)C₅₀ value between >1000 and <3000 mg active acid/L and of 1000 mg active acid/L have been determined for the effects of the test substance on the mortality of the marine fish species Cyprinodon variegatus and the marine amphipod Paleomonetes pugio, respectively.

Short-term freshwater toxicity data are available with HMDTMP acid for fish, invertebrates and algae:
Fish: 14 -day LC₅₀ 440 mg active acid/L, Oncorhynchus mykiss

Invertebrates: 48-hour EC₅₀ 570 mg active acid/L, Daphnia magna

Algae: 96-hour EC₅₀ 28 mg active acid/L and 96-hour NOEC 10 mg active acid/L (calculated by reviewer), Scenedesmus subspicatus (new name: Pseudokirchneriella subcapitata)

A long-term toxicity to invertebrate study has been read across from a structurally similar substance, ATMP acid (EC 229-146-5, CAS 6419-19-8). A 28-day NOEC of  ≥ 25 mg active acid/L was calculated for the effects of ATMP acid on the adult survival and reproduction of Daphnia magna.

A long-term toxicity to fish study has been read-across from a structurally similar substance, ATMP acid (EC 229-146-5, CAS 6419-19-8).

A 60-day NOEC of 23 mg active acid/L was calculated for the effects of ATMP acid on the length and weight of Oncorhynchus mykiss fry.

A toxicity to microorganisms (ASRI) study has been read-across from a structurally similar substance, EDTMP sodium salt (EC 244-742-5, CAS 22036-77-7). A 3-hour EC₅₀ of > 100mg active acid/L was calculated for the effects of EDTMP sodium salt on the inhibition of respiration of waste-water treatment plant microorganisms.

Additional information

The acid, sodium and potassium salts in the HMDTMP category are freely soluble in water. The HMDTMP anion can be considered fully dissociated from its sodium or potassium cations when in dilute solution. Under any given conditions, the degree of ionisation of the HMDTMP 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 HMDTMP-H, HMDTMP.4Na, HMDTMP.7K or another salt of HMDTMP.

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

1. HMDTMP is present as HMDTMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether HMDTMP (4-7K) salt, HMDTMP (4-7Na) salt, HMDTMP-H (acid form), or another salt was used for dosing.

2. Disassociated potassium or sodium cations. The amount of potassium or sodium present depends on which salt was added.

3. It should also be noted that divalent and trivalent cations would preferentially replace the sodium or potassium ions. These would include calcium (Ca²⁺), magnesium (Mg²⁺) and iron (Fe³⁺). These cations are more strongly bound by HMDTMP than potassium and sodium. This could result in HMDTMP-dication (e.g. HMDTMP-Ca, HMDTMP-Mg) and HMDTMP-trication (e.g. HMDTMP-Fe) complexes being present in solution.