Registration Dossier

Administrative data

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 4.21 of IUCLID and Section 1 of the CSR describe 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 potassium salts will fully dissociate in aqueous solution and will behave no differently to the parent HEDP acid and its potassium counter ion at equivalent concentrations. It is not expected that the potassium 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 the 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. In in vivo toxicity studies the local pH and ionic conditions within the stomach, gastrointestinal tract etc. dominate the dissociation state of the phosphonate, irrespective of the form originally dosed. At a 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 to yield HEDP acid and counter-ion. Hence some properties (in contact with water or in aqueous media, i.e. ecotoxicity) for a salt can be directly read across (with suitable mass correction, see Section 1.4 of the CSR) to the parent acid and vice versa. In the present context the effect of an alkaline metal counterion (sodium/potassium) will not be significant and has been extensively discussed in the public literature. In biological systems, polyvalent metal ions will be present, and the phosphonate ions show very strong affinity to them. The ammonium salt does present a particular issue since ammonia drives the toxicity of the substance and will be assessed separately.

The behaviour of phosphonates in the environment will be profoundly affected by their concentration in water, the concentration and identities of metal ions, and the solids content per unit volume of water. From surface water through to soil a wide range of these parameters will be exhibited. Very few data concerning background concentrations of phosphonates in the environment are published, possibly due to the difficulties in detecting these substances at low concentrations in environmental media. Almost all natural waters contain more ions than the usual PEC values of the phosphonates.

In addition, in the environment the salt form is immaterial and speciation will occur in natural media. Similarly, all environmental related endpoints, use of buffered test media results often reflect a salt speciation relevant for ~pH 7 only and it would be impossible to test specific salts associated with high and low pH. Detaching or attracting a proton does not change the chemical safety assessment of the molecule as long as no other part of the molecular skeleton is changed, because in studies or when there is exposure, the pH will control the identity of the form or forms present.

Therefore. it is considered appropriate to read-across between the HEDP category members and attribute the effects to the acid component of the phosphonate.

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 sodium is not classified for the environment.