Sodium salts of [[(phosphonomethyl)imino]bis[ethane-2,1-diylnitrilobis(methylene)]]tetrakisphosphonic acid (1-3 Na:1)

Endpoint summary

Description of key information

DTPMP sodium salts will fully dissociate in aqueous solution and will behave no differently to the parent DTPMP acid and the sodium counter ions at equivalent concentrations. It is not expected that the counter ion will contribute significantly to the toxicity of the registration substance. Therefore, the impact on aquatic organisms will be dominated by the effects of the DTPMP acid.

Short-term data are available for all three trophic levels:
Fish:

Freshwater 96h LC₅₀ 180 -252 mg active acid/L, Onchorhynchus mykiss. Marine 96 h LC₅₀ 6435 mg active acid/L, Cyprinodon variegatus

Invertebrates:

Freshwater 48 h EC₅₀ 9910 mg active acid/L, Chironomus tentans. Marine 96 h LC₅₀ >250 mg active acid/L, Acartia tonsa

Algae:

Freshwater 95 h ErC₅₀ >10 mg active acid/l, Pseudokirchneriella subcapitata (reported as Selenastrum capricornutum).

Long-term data are available for all three trophic levels:

Fish:

Freshwater 60 d NOEC 25.6 mg active acid/L, Salmo gairdneri (new name: Oncorhynchus mykiss).

Invertebrates:

Freshwater 28 d NOEC ≥ 25 mg active acid/L, Daphnia magna. Marine 96 h NOEC 67 mg active acid/L and an EC₅₀ 187 mg active acid/L, Crassostrea virginica

Algae

Freshwater 95 h NOErC ≥10 mg active acid/L, Pseudokirchneriella subcapitata (reported as Selenastrum capricornutum).

Microorganisms

There are no reliable data describing the short-term toxicity of DTPMP to sewage sludge micro-organisms. However data have been read-across from other phosphonic acids. The data indicate a low level of toxicity (200 mg/l).

Additional information

The acid and salts in the DTPMP category are freely soluble in water and, therefore, the DTPMP anion is fully dissociated from its cations when in solution. Under any given conditions, the degree of ionisation of the DTPMP 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 DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP (4-8K), DTPMP (xNH4) or another salt of DTPMP.

 

Therefore, when a salt of DTPMP is present in test media or the environment, the following is present (separately):

1. DTPMP is present as DTPMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP (4-8K), DTPMP (xNH4), or another salt was used for testing.

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

3. Divalent and trivalent cations have much higher stability constants for binding with DTPMP than the sodium, potassium or ammonium 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 DTPMP-dication (e.g. DTPMP-Ca, DTPMP-Mg) and DTPMP-trication (e.g. DTPMP-Fe) complexes in solution, irrespective of the starting substance/test material.