Reaction mass of [[(2-hydroxyethyl)imino]bis(methylene)]bisphosphonic acid and Phosphonic acid, P-[(tetrahydro-2-hydroxy-2-oxido-4H-1,4,2-oxazaphosphorin-4-yl)methyl]-

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.2 mg/L

Assessment factor:

50

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.46 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.02 mg/L

Assessment factor:

500

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

80 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

55.7 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

5.57 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:

5.07 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The HEBMP category covers the acid form and various sodium salts of [[(2-hydroxyethyl)imino]bis(methylene)]-bisphosphonic acid, equilibrium mixture with 4-(Phosphonomethyl)-2-hydroxy-2-oxo-1,4,2-oxazaphosphorinane (cyclic form). The different salts are prepared by neutralising the acid to a specific pH. All category members are based on the HEBMP structure. Measured data are available for some salts and the acid form. The substances are commercially available as aqueous solutions only and in an environmental context the speciation will be the same. The properties of the members of the category are consistent across all endpoints.The category hypothesis is that all the members are various ionised forms of the same parent acid constituents, which coexist in solution at an equilibrium defined by the pH. The main assumption is that sodium is not significant in respect of all the properties under consideration. In dilute aqueous conditions of defined pH a salt of a constituent will behave no differently to the constituent parent acid, at identical concentration of the particular speciated form present, and will be fully dissociated. Hence some properties (measured or expressed in aqueous media, e.g. ecotoxicity) for a salt can be directly read-across (with suitable mass correction) to the parent acid constituent and vice versa, and from one salt to another.

HEBMP-H 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 HEBMP-H and its salts to environmental species is presented and interpreted in terms of the concentration of active HEBMP acid in the test media. As such the results of tests conducted on HEBMP-H 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 pK_a values for the ionisation of HEBMP. Four pK_a values, of 1.3, 2.7, 5.9 and >8 have been reported for the non-cyclic HEBMP constituent and three pK_a values have been reported for the cyclic constituent: 1.3, 2.7 and 7.3. At environmentally-relevant pH values, HEBMP will typically be ionised around 1-3 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.

Please refer to IUCLID Section 13 and Annex 3 of the CSR for justification of read-across within the HEBMP 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 is 46 mg/l (72 hour, algae Pseudokirchneriella subcapitata).

Hazards to the aquatic environment (long-term): Category Chronic 3 on the basis of the lowest E(L)C₅₀ in short-term test results in fish, invertebrates and algae is 46 mg/l (72 hour, algae Pseudokirchneriella subcapitata). When assessed according to the available long-term data, the substance is concluded as not classified (based on long-term EC₁₀/NOEC values >1 mg/l). Therefore, the most stringent outcome is selected, and the substance is classified as Category Chronic 3.