Strontium neodecanoate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.123 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.012 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

78.1 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.71 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.071 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:

0.069 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.019 g/kg food

Assessment factor:

90

Additional information

Reliable acute aquatic toxicity data of strontium neodecanoate are available from GLP-conform guideline studies for algae, daphnia, fish and microorganisms. Respective EC/LC50 values are well above respective test limits of 100 mg/L, i.e., 96-h LC50 for fish (Danio rerio): >299.7 mg/L, 48-h EC50 for immobilisation of Daphnia magna: >299.7 mg/L, 72-h EC50 for algal growth rate (Pseudokirchneriella subcapitata): >250 mg/L, 3-h EC50 for the respiration inhibition of activated sludge: >871.3 mg/L. Therefore, strontium neodecanoate has a low potential for acute toxicity to aquatic organisms.

Reliable chronic aquatic toxicity data of strontium neodecanoate are available from GLP-conform guideline studies for algae and microorganisms. Respective EC10 values are well above 100 mg/L, i.e., 72-h EC10 for algal growth rate (Pseudokirchneriella subcapitata): 129 mg/L, 3-h EC10 for the respiration inhibition of activated sludge: >871.3 mg/L. Thus, strontium neodecanoate has a low potential for chronic toxicity to aquatic algae and microorganisms.

 

In sum, reported substance-specific L(E)C50 and chronic EC10 values of strontium neodecanoate are well above aquatic hazard criteria as summarised in the Table below. Based on read-across of acute and chronic toxicity data available for soluble strontium substances, strontium neodecanoate does also not meet aquatic hazard criteria. 

 

Table: Acute and chronic aquatic toxicity data for strontium neodecanoate and its dissolved ions

Trophic level	Endpoint	Strontium neodecanoate	Strontium	Neodecanoic acid
Short-term
Algae	72-h EC50	>250 mg/L	>47.1 mg/L	>100 mg/L
Daphnia	48-h LC50	>299.7 mg/L	125 mg/L	>1000 mg/L
Fish	96-h LC50	>299.7 mg/L	>56.3 mg/L	>100 mg/L
Long-term
Algae	72-h EC10	129 mg/L	24.3 mg/L	-
Daphnia	NOEC	-	21 mg/L	3.4 mg/L (7-day NOEC for Ceriodaphnia dubia)
Fish	NOEC	-	-	1.1 mg/L (based on 30-day Chronic Value predicted by QSAR)
Microorganisms	NOEC/EC10	>871.3 mg/L	>163.8 mg/L	>100 mg/L

 

Read-across approach

Metal carboxylates are substances consisting of a metal and a carboxylic acid. Based on the solubility of strontium neodecanoate in water (8.47 g dissolved Sr/L at pH 8.4 corresponding to 45.07 g strontium neodecanoate/L), a complete dissociation of strontium neodecanoate resulting in strontium and neodecanoate 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 neodecanoate 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 neodecanoate 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 K_ML) of strontium with other carboxylic acids, i.e. acetic, propanoic and butanoic acid, ranging from 0.78 to 0.89, 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 K_ML= α_O* log K_HL+ β_O; where

K_MLis the metal-ligand formation constant, K_HLis the corresponding proton–ligand formation constant, and α_Oand β_Oare termed the Irving–Rossotti slope and intercept, respectively. Applying the equation and parameters derived by Carbonaro & Di Toro (2007) and the pKa of neodecanoic acid of 4.69 results in:

log K_ML= 0.160 * 4.69 + 0.069

log K_ML= 0.82 (estimated strontium-neodecanoate formation constant).

Thus, it may reasonably be assumed that based on the estimated strontium-neodecanoate formation constant, the respective behaviour of the dissociated strontium cations and neodecanoate anions in the environment determine the fate of strontium neodecanoate upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning resulting in a different relative distribution in environmental compartments (water, air, sediment and soil) and subsequently its ecotoxicological potential.

Therefore, in the assessment of the ecotoxicity of strontium neodecanoate, read-across to neodecanoic acid (CAS 26896-20-8; EC 248-093-9) and soluble strontium substances is applied since the ions of strontium neodecanoate determine its ecotoxicological potential.

 

Reference:

Carbonaro RF & Di Toro DM (2007) Linear free energy relationships for metal–ligand complexation: Monodentate binding to negatively-charged oxygen donor atoms. Geochimica et Cosmochimica Acta 71: 3958–3968.

Conclusion on classification

Strontium neodecanoate dissolves and dissociates into strontium and neodecanoate ions upon contact with an aqueous medium. Therefore, the aquatic hazard potential is assessed based on the substance-specific toxicity data as well as toxicity data available for strontium and neodecanoate.

Reliable acute aquatic toxicity data of strontium neodecanoate are available from GLP-conform guideline studies for algae, daphnia and fish; respective EC/LC50 values are well above 100 mg/L. Therefore, strontium neodecanoate does not meet classification criteria as short-term hazard to the aquatic environment under Regulation (EC) No 1272/2008 and subsequent adaptations.

Reliable chronic aquatic toxicity data of strontium neodecanoate are available from GLP-conform guideline studie for algae, the respective EC10 value is well above 100 mg/L. Chronic fish and daphnia toxicity data are lacking for strontium neodecanoate. However, chronic aquatic toxicity of strontium and neodecanoate to daphnia as well as chronic toxicity of neodecanoate to fish is not observed and/or estimated at or below 1 mg/L.

Solely, long-term toxicity to fish has not been quantified sufficiently. Thus, adequate chronic toxicity data are not available for one trophic level. Criteria given in Table 4.1.0(b) iii) are applied in accordance with Figure 4.1.1 of Regulation (EC) No 1272/2008. The 96-h LC 50 for fish of strontium neodecanoate is > 299.7 mg/L and thus above the classification criteria for substances for which adequate chronic toxicity data are not available. Therefore, strontium neodecanoate does not meet classification criteria as long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008 and subsequent adaptations.