Magnesium neodecanoate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.509 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.051 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

no hazard identified

Sediment (marine water)

Hazard assessment conclusion:

no hazard identified

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.018 g/kg food

Assessment factor:

90

Additional information

The fate and toxicity of magnesium neodecanoate in the environment is most accurately evaluated by separately assessing the fate of its moieties magnesium and neodecanoate.

Magnesium neodecanoate dissolves and dissociates into magnesium and neodecanoate ions upon contact with an aqueous medium. Therefore, the aquatic hazard potential is assessed based on the toxicity data available for magnesium and neodecanoate since the ions of magnesium neodecanoate determine its environmental fate and toxicity.

Acute (short-term) toxicity data: As an essential element for living organisms magnesium has a very low potential for acute toxicity to freshwater as well as saltwater organisms. Regarding aquatic toxicity data for neodecanoate, data are available from GLP-conform guideline studies for three trophic levels: algae, invertebrates and fish. In sum, reported L(E)C50 values of both magnesium and neodecanoate are well above 100 mg/L and corresponding OECD test limits.

Chronic (long-term) toxicity: As an essential element for living organisms, magnesium has a very low potential for long-term toxicity to freshwater as well as saltwater organisms. Regarding aquatic toxicity data for neodecanoate, reliable data are available for invertebrates from a structural analogue (neoheptanoic acid) and QSAR-based estimates for daphnids as well as long-term toxicity data on freshwater fish, also supported by QSAR-based estimates. The respective NOEC/EC10 values are > 1 mg/L. Regarding algae, an EC10 or NOEC is not available for neodecanoate. However, based on the fact that the EC50 for growth rate of algae is > 100 mg/L, it is unlikely that the EC10/NOEC < 1 mg/L. Thus, chronic aquatic toxicity of magnesium neodecanoate to algae, daphnia and fish is not expected below 1 mg/L.

 

Read-across approach

Metal carboxylates are salts consisting of metal cations and carboxylic acid anions. Based on the solubility of magnesium neodecanoate in water (37.2 g/L at 30 °C), a complete dissociation of magnesium neodecanoate resulting in magnesium cations and neodecanoate anions may be assumed under environmental conditions. The respective dissociation is in principle 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 magnesium 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 magnesium to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as neodecanoate are not expected to bind strongly with magnesium. Accordingly, protons will always out-compete magnesium ions for complexation of monodentate ligands given equal activities of free magnesium and hydrogen ions. The metal-ligand formation constants (log KML) of magnesium with other carboxylic acids, i.e. acetic and benzoic acid, ranging from 0.1 to 0.82 (Bunting & Thong, 1969), further point to a low strength of the monodentate bond between carboxyl groups and magnesium.

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 neodecanoic acid of 4.69 results in:

log KML= 0.148 * 4.69 + 0.216

log KML= 0.910 (estimated magnesium-neodecanoate formation constant).

Thus, it may reasonably be assumed that based on the estimated magnesium-neodecanoate formation constant, the respective behaviour of the dissociated magnesium cations and neodecanoate anions in the environment determine the fate of magnesium 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.

Thus, in the assessment of environmental toxicity of magnesium neodecanoate, read-across to neodecanoate and soluble magnesium substances is applied since the individual ions of magnesium neodecanoate determine its environmental fate.Since magnesium ions and neodecanoate ions behave differently in the environment, regarding their fate and toxicity, a separate assessment of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity.

 

In order to evaluate the environmental fate of the substance magnesium neodecanoate, information on the assessment entities magnesium cation and neodecanoate anion were considered. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for magnesium neodecanoate.

 

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

Aquatic toxicity studies with magnesium neodecanoate are not available, thus aquatic toxicity is addressed with existing data on the dissociation products. Magnesium neodecanoate dissolves and dissociates into magnesium and neodecanoate ions upon contact with an aqueous medium. Magnesium is naturally ubiquitous in the environment and essential for living organisms with a very low potential for toxicity to freshwater and saltwater organisms. Adverse effects are lacking up to and including the respective OECD/EC guidelines limit concentrations. The aquatic hazard assessment is therefore based on the most toxic moiety, i.e. the neodecanoate anion. Existing aquatic toxicity data of neodecanoate are recalculated for magnesium neodecanoate based on a maximum neodecanoate content of 93.9%.

 

Acute (short-term) toxicity data:

As an essential element for living organisms magnesium has a very low potential for acute toxicity to freshwater as well as saltwater organisms. Regarding aquatic toxicity data for neodecanoate, data are available from GLP-conform guideline studies for three trophic levels: algae, invertebrates and fish. In sum, reported L(E)C50 values of both magnesium and neodecanoate are well above 100 mg/L and corresponding OECD test limits. Therefore, magnesium neodecanoate 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:

As an essential element for living organisms magnesium has a very low potential for long-term toxicity to freshwater as well as saltwater organisms. Regarding aquatic toxicity data for neodecanoate, reliable data are available for invertebrates from a structural analogue (neoheptanoic acid) and QSAR-based estimates for daphnids as well as long-term toxicity data on freshwater fish, also supported by QSAR-based estimates. The respective NOEC/EC10 values are > 1 mg/L. Regarding algae, an EC10 or NOEC is not available for neodecanoate. However, based on the fact that the EC50 for growth rate of algae is > 100 mg/L, it is unlikely that the EC10/NOEC < 1 mg/L. Thus, chronic aquatic toxicity of magnesium neodecanoate to algae, daphnia and fish is not expected below 1 mg/L.

Based on the surrogate approach (Table 4.1.0 (b) (iii), magnesium neodecoate would also not meet chronic classification criteria since the EC50 for algae > 100 mg/L. Therefore, magnesium neodecanoate does not meet classification criteria as long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008.

 

In sum, based on read-across of toxicity data available for magnesium and neodecanoate, magnesium neodecanoate dose not meet classification criteria as acute (short-term) or long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008 and its subsequent adaptations.