Etidronic acid

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.068 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.007 mg/L

Assessment factor:

1 000

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:

136 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

13.6 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:

10 mg/kg soil dw

Assessment factor:

50

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

3.7 mg/kg food

Assessment factor:

30

Additional information

HEDP 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 describes the pKa values for the ionisation of HEDP. Four pKa values of HEDP are reported, of 1.7, 2.47, 7.28, 11.41. At environmentally-relevant pH values HEDP will be ionised typically three 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.

 

HEDP sodium salts will fully dissociate in aqueous solution and will behave no differently to the parent HEDP acid and its sodium counter ion at equivalent concentrations. It is not expected that the sodium counter ion will contribute significantly to the overall toxicity of their HEDP salts. Therefore, the impact on aquatic organisms will be dominated by the effects of the HEDP acid and PNECs are derived in terms of HEDP acid.

 

Read-across between HEDP salts and the parent acid substance is considered appropriate because:

The category hypothesis is that all the members are various ionised forms of the acid CAS 2809-21-4. The main assumption is that sodium and potassium are not significant in respect of all the properties under consideration. HEDP salts will dissociate into HEDP and the counter-ion when in contact with aqueous and moist media, therefore the two substances should be assessed separately. In dilute aqueous conditions of defined pH a salt will behave no differently to the parent acid, at identical concentration of the particular speciated form present and will be fully dissociated. Hence some properties for a salt can be directly read-across (with suitable mass correction) to the parent acid and vice versa.

Conclusion on classification

Not classified according to Regulation (EC) No 1272/2008 classifiable based on the fact that short term toxicity data are >100 mg/L. In addition, the NOEC for long term toxicity with invertebrates is >1 mg/L therefore HEDP-H is not classified for the environment.