[[(phosphonomethyl)imino]bis[ethylenenitrilobis(methylene)]]tetrakisphosphonic acid, ammonium salt

Endpoint summary

Description of key information

Limited data are available on the toxicity of DTPMP-xNH₄ to aquatic organisms. DTPMP-xNH₄ will dissociate as it is released into the aquatic environment and it is therefore necessary to assess the hazard properties of DTPMP and ammonia separately. For hazard classification, the DTPMP-xNH₄ has been assessed based on the available aquatic data for the whole substance (based on read-across data from the ammonium salt of ATMP, a structurally analogous substance).

DTPMP:

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

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

Invertebrates:

Freshwater 48 h EC₅₀ 66 mg/L, Daphnia magna (weight-of-evidence (WOE))
Freshwater 48 h EC₅₀ 9910 mg active acid/L, Chironomous tentans (WOE)

Marine 96 h LC₅₀ >250 mg active acid/L, Acartia tonsa (WOE)

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, read-across from structural analogues:

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 lack of inhibition of microorganisms at concentrations ≥ 200 mg/L. These data are read-across from HEDP-H and ATMP-H.

Additional information

DTPMP-xNH₄ will dissociate when it is released into aqueous environments to yield DTPMP and ammonia.

Ammonia:

The toxicity of the ammonium salt will be significantly influenced by the presence of ammonia that is liberated following dissociation and its contribution therefore needs to be taken account of when determining hazard and when setting PNECs for risk characterisation. For hazard classification, the DTPMP-xNH₄ has been assessed based on the available aquatic data for the whole substance (based on read-across data from the ammonium salt of ATMP, a structurally analogous substance).

 

Ammonia ecotoxicity data have been reviewed in two programmes of peer review: the Environment Agency Proposed EQS for Water Framework Directive Annex VIII Substances: Ammonia (unionised) 2007 (EA, 2007) and the OECD/HPV SIAR for the Ammonia category (OECD, 2007; sponsored by, shared partnership with European Fertilizers Manufacturing Association (EFMA-Europe) and The Fertilizer Institute (TFI-US)). Further review of the data has not been considered necessary.

 

The following aquatic data have been selected as the lowest reliable freshwater values (expressed in terms of unionised NH₃) available from the peer-reviewed report 'Environment Agency Proposed EQS for Water Framework Directive Annex VIII Substances: Ammonia (unionised) 2007' (EA, 2007):

Short-term

Fish: 96-hour LC₅₀ 0.068 mg NH₃-N/L, Oncorhynchus gorbuscha (equivalent to 0.083 mg NH₃/L)

Invertebrates: 96-hour LC₅₀ 0.16 mg NH₃-N/L, Hyalella azteca

Algae: 5-day EC₅₀ 2.0 mg NH₃-N/L, Chlorella vulgaris

Long-term

Fish: 73-day LOEC 0.022 mg NH₃-N/L, Oncorhynchus mykiss (equivalent to 0.027 mg NH₃/L). This value is converted to a NOEC value by applying a factor of 2, therefore the 73-day NOEC value is 0.0135 mg NH₃/L.

Invertebrates: 29-day NOEC 0.066 mg NH₃-N/L, Deleatidium sp.

Algae: 14-day LOEC 3.0 mg NH₃-N/L, mixed algal populations

Peer-reviewed aquatic ecotoxicity data have also been reviewed in the OECD SIDS (2007) report, however the data from the Environment Agency (2007) report represent the lowest available data for these endpoints. Across both datasets, fish were the most sensitive trophic level in both short- and long-term tests. Therefore, the long-term fish data has been used as the basis of the aquatic PNEC values.

The toxicity of the ammonium salt is discussed further in IUCLID Section 6.0 Ecotoxicological Information and section 7.0 of the CSR.

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 introduced into 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.

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