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Ecotoxicological Summary

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Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.44 mg/L
Assessment factor:
50
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
0.61 mg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.04 mg/L
Assessment factor:
500
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
88.52 mg/L
Assessment factor:
1

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
7.86 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
0.79 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:
1.31 mg/kg soil dw
Extrapolation method:
equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

Read-across approach

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of strontium 2-ethylhexanoate in water, a complete dissociation of strontium 2-ethylhexanoate resulting in strontium and 2-ethylhexanoate ions may be assumed under environmental conditions. The respective dissociation is reversible and the ratio of the salt /dissociated ions is dependent on the metal-ligand dissociation constant of the salt, the composition of the solution and its pH.

A metal-ligand complexation constant of strontium 2-ethylhexanoate could not be identified. Data for alkaline earth metals appear to be generally limited. However, alkaline earth metals tend to form complexes with ionic character as a result of their low electronegativity. Further, the ionic bonding of alkaline earth metals is typically described as resulting from electrostatic attractive forces between opposite charges, which increase with decreasing separation distance between ions. Based on an analysis by Carbonaro & Di Toro (2007) of monodentate binding of strontium to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as 2-ethylhexanoate are not expected to bind strongly with strontium. Accordingly, protons will always out-compete strontium ions for complexation of monodentate ligands given equal activities of free strontium and hydrogen ions. The metal-ligand formation constants (log KML) of strontium with other carboxylic acids, i.e. acetic and benzoic acid, ranging from 0.1 to 0.47, further point to a low strength of the monodentate bond between carboxyl groups and strontium.

The analysis by Carbonaro & Di Toro (2007) suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms of carboxylic functional groups:

log KML= αO* log KHL+ βO; where

KML is the metal-ligand formation constant, KHL is the corresponding proton–ligand formation constant, and αO and βO are termed the Irving–Rossotti slope and intercept, respectively. Applying the equation and parameters derived by Carbonaro & Di Toro (2007) and the pKa of 2-ethylhexanoic acid of 4.72 results in:

log KML= 0.160 * 4.72 + 0.069

log KML= 0.824 (estimated strontium-ethylhexanoate formation constant).

Thus, in the assessment of environmental toxicity of strontium 2-ethylhexanoate, read-across to the assessment entities 2-ethylhexanoate and soluble strontium substances is applied since the individual ions of strontium 2-ethylhexanoate determine its toxicity. Since strontium ions and 2-ethylhexanoate ions behave differently in the environment, a separate assessment of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for strontium 2-ethylhexanoate.

Conclusion on classification

Aquatic toxicity studies with strontium 2-ethylhexanoate are not available, thus aquatic toxicity is addressed with existing data on the dissociation products. Strontium is naturally ubiquitous in the environment and has a relatively low potential for toxicity to freshwater and saltwater organisms and effect concentzration are unbound (adverse effects are lacking up to and including the highest test concentration) or are above the respective OECD/EC guidelines limit concentrations. The aquatic hazard assessment is based on the most toxic moiety, i.e. the 2-ethylhexanoate anion. Existing aquatic toxicity data of 2-ethylhexanoic acid are recalculated for strontium 2-ethylhexanoate based on a maximum 2-ethylhexanoate content of 81 %.

Acute (short-term) toxicity: Reliable acute aquatic toxicity data are available from guideline studies for algae, daphnia, and fish. The lowest EC/LC50 values are 60.9 mg/L, 105.4 mg/L and > 123.5 mg/L, respectively, and are well above the classification cut-off value for acute (short-term) aquatic hazard category 1. Therefore, strontium 2-ethylhexanoate does not meet classification criteria as short-term hazard to the aquatic environment under Regulation (EC) No 1272/2008 and its subsequent adaptations.

Chronic (long-term) toxicity: Reliable chronic aquatic toxicity data are available from guideline studies for algae and daphnia. The lowest respective EC10/NOEC values are 39.5 mg/L and 22.2 mg/L, respectively, and are well above the classification cut-off values for long-term aquatic hazard category 1 -3. Since long-term data are not available for fish, the surrogate approach is applied. Based on classification criteria for substances for which adequate chronic toxicity are not availlable in Table 4.1.0 (b) (III), Figure 4.1.1 and adequate acute toxicity data of fish with LC50 values > 123.5 mg/L, strontium 2 -ethylhexanoate does not classify as long-term aquatic hazard category 1 -3. Criteria for classification in category 4 are also not met. Therefore, strontium 2-ethylhexanoate does not meet classification criteria as long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008 and its subsequent adaptations.