[nitrilotris(methylene)]trisphosphonic acid, sodium salt

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.4 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.04 mg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

20 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

603 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

60 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

4.73 mg/kg soil dw

Assessment factor:

100

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

ATMP and its salts are phosphonic acid substances of very high water solubility, and low octanol-water partition coefficient. The phosphonic acid groups are multiply ionised at pH values relevant to biological and environmental systems. Ionisation gives them the ability to form stable complexes with metal ions, particularly polyvalent ones. Phosphonates are found to adsorb strongly to inorganic matrices, and hence they adsorb strongly to sewage sludge and to soil. They will be removed to a high extent in biological waste water treatment by adsorption.

The toxicity of ATMP and its salts to environmental species is presented and interpreted in terms of the concentration of active ATMP acid in the test media. As such the results of tests conducted on ATMP and its salts are directly comparable, because the ionisation state will depend only on the pH of the test medium. At environmentally-relevant pH values ATMP will be ionised typically four or five times, and will form stable complexes with metal ions.

The substances have the potential to cause effects on aquatic plants as a consequence of nutrient limitation caused by complexation of trace metals. As complexing agents, these substances could remobilise metals in the environment; however, their high degree of adsorption to sediments suggests that this is unlikely to occur. The substances are acids and when present at high concentration they have the potential to cause local effects on aquatic organisms as a consequence of lowered pH.

Effects on aquatic organisms arising from exposure to the acid form of the substance are thought to result from a reduction in the pH of the ambient environment (arising from an increase in the H⁺concentration) to a level below their tolerable range. It is not considered appropriate or useful to derive a PNEC with studies in which pH deviations may have been attributable to the cause of effects seen because any effects will not be a consequence of true chemical toxicity and will be a function of, and dependent on, the buffering capacity of the environment.

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.

Please refer to IUCLID Section 13 and Annex 3 of the CSR for further details of read-across within the ATMP category.

Conclusion on classification

Hazards to the aquatic environment (acute/short-term): not classified on the basis of the lowest E(L)C₅₀ in short-term test results in fish, invertebrates and algae being >1 mg active acid/L (Pseudokirchneriella subcapitata).

Hazards to the aquatic environment (long-term): not classified on the basis of the lowest NOEC or E(L)C₁₀ in long-term test results in fish, invertebrates and algae being ≥1 mg active acid/L (Oncorhynchus mykiss).