(1-hydroxyethylidene)bisphosphonic acid, potassium salt

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.675 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.068 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

40 mg/L

Assessment factor:

5

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1 350 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

135 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:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

HEDP acid 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 HEDP and its salts to environmental species is presented and interpreted in terms of the concentration of active HEDP acid in the test media. As such, the results of tests conducted on HEDP and its salts are directly comparable, because the ionisation state will depend only on the pH of the test medium. Section 1 of the CSR and IUCLID Section 4.21 describe the pKa values for the ionisation of HEDP. Four pKa values of 1.7, 2.47, 7.28, 10.29 are reported in the key study at 25°C (Martell 1968). At environmentally-relevant pH values HEDP will be ionised typically around two to three times, and will form stable complexes with metal ions.

 

HEDP acid and its salts 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.

Open sea PNEC

HEDP acid and its salts are used in some scenarios (offshore oilfield) in open sea. The methodology of CHARM (2005) has been used to derive the PNEC for risk characterisation in this setting. These can be found in Section 7.6 of the CSR.

The acid, sodium and potassium salts in the HEDP category are freely soluble in water and, therefore, the HEDP anion is fully dissociated from its sodium or potassium cations when in solution. Under any given conditions, the degree of ionisation of the HEDP 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 HEDP-H, HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK or another salt of HEDP.

 

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

1. HEDP is present as HEDP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the system and not whether HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK salts, HEDP-H or another salt was added.
2. Disassociated sodium/potassium cations. The amount of sodium/potassium present depends on which salt was added.
3. Divalent and trivalent cations have much higher stability constants for binding with HEDP than the sodium or potassium 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 HEDP-dication (e.g. HEDP-Ca, HEDP-Mg) and HEDP-trication (e.g. HEDP-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 HEDP Category is considered to be valid.

Please refer to IUCLID Section 13 and Annexes 3 and 4 of the CSR for justification of read-across within the HEDP category, and read-across from the ATMP and DTPMP categories for the long-term fish endpoint.

CHARM (2005) CHARM Chemical Hazard Assessment and Risk Management for the use and discharge of chemicals used offshore. User Guide Version 1.4.

Conclusion on classification

There are long-term data available for three trophic levels: fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata). HEDP-xK is not readily biodegradable and has a low log K_ow value. Therefore, it is not classified according to Regulation (EC) No 1272/2008, based on the following:

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 >10 mg active acid/L.

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.