[nitrilotris(methylene)]trisphosphonic acid, ammonium salt

Endpoint summary

Description of key information

Due to its high adsorption and low toxicity to aquatic organisms, ATMP was assigned to soil hazard category 3 and a screening assessment was conducted, based on the equilibrium partitioning method (PEC * 10 / PNECscreen). Confirmatory testing for long-term toxicity to terrestrial organisms has been carried out with one trophic level, earthworms (consumers). PNECsoil has been derived using both the equilibrium partitioning method and measured terrestrial ecotoxicity data and the most conservative value (PNECsoil based on measured terrestrial ecotoxicity data) has been used for PNECsoil in the chemical safety assessment. As the terrestrial RCRs based on this PNEC are < 1, no further toxicity testing of soil organisms is currently considered to be necessary.

Additional information

ATMP-xNH₄ will dissociate into ATMP and ammonia when it is released into soils where water is present. ATMP and ammonia will therefore be treated separately for the purposes of deriving PNECs for soils.

As an inorganic ion, ammonium is ubiquitous in the environment, is not bioaccumulative and is highly water soluble. Test data for the derivation of PNECs for ammonia for the protection of soil-dwelling organisms are therefore not required. Therefore the RCR has been based on ATMP.

There are no data available on the effects of ATMP-xNH₄ on terrestrial (soil-dwelling) organisms, therefore studies have been read-across from ATMP-H and from other analogous phosphonate substances.

Three long-term studies have been read-across to ATMP-xNH₄ and its salts from structurally analogous substances as part of a weight of evidence approach to fulfil the soil macroorganisms except arthropods endpoint. The following data are selected for chemical safety assessment for this endpoint: HEDP-H: 56-day NOEC and EC₅₀ values of 472.5 and >945 mg active acid/kg soil dry weight, reproduction, Eisenia fetida (Noack, 2014). A second, reliable study is read-across from HMDTMP(4-7K), which reports 56-day EC₁₀ and EC₅₀ values of 543 and >1000 mg active acid/kg soil dry weight, based on reproduction for Eisenia fetida (Noack, 2020). Whilst a reliable study is available for the ATMP category (ATMP-xNa) (Noack, 2021), the effects are attributed to the sodium cation, instead of the ATMP anion. This is further explained in a separate report, attached in IUCLID Section 13 (PFA, 2021).

Two short-term studies are available with ATMP-H which indicate no toxicity to the earthworm Eisenia fetida and the plant Avena sativa at the highest test concentrations tested, i.e. NOEC ≥960 mg/kg dwt (Henkel, 1984). However, insufficient details on the studies are presented in the report and they have been assigned reliability 4.

 

ATMP and its salts are highly adsorbing to soil and soil mineral substrates. The nature of the adsorption is believed to be primarily due to interaction with inorganic substrate or generalised surface interactions. High adsorption is consistent with similar behaviour seen for the analogues DTPMP and HEDP, and other common complexing agents such as EDTA. By reference to findings with other similar substances, the binding occurs very rapidly and is effectively irreversible. For environmental fate purposes in exposure assessment this is assessed as a removal process.

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

 

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

1. ATMP is present as ATMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether ATMP (3-5K) salt, ATMP (3-5Na) salt, ATMP-H (acid form), or another salt was used for dosing.
2. Disassociated potassium, sodium or ammonium cations. The amount of potassium or sodium present depends on which salt was dosed.
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 ATMP than potassium, sodium and ammonium. This could result in ATMP-dication (e.g. ATMP-Ca, ATMP-Mg) and ATMP-trication (e.g. ATMP-Fe) complexes being present in solution.

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