Magnesium 2-ethylhexanoate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.391 mg/L

Assessment factor:

50

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.535 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.039 mg/L

Assessment factor:

500

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

77.78 mg/L

Assessment factor:

1

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

6.91 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.691 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:

1.15 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The fate and toxicity of magnesium 2-ethylhexanoate in the environment is most accurately evaluated by separately assessing the fate of its moieties magnesium and 2-ethylhexanoate.

 

Magnesium2-ethylhexanoatedissolves and dissociates into magnesium and 2-ethylhexanoateions upon contact with an aqueous medium. Therefore, the aquatic hazard potential is assessed based on the toxicity data available for magnesium and 2-ethylhexanoate and read-across to the assessment entities soluble magnesium substances and 2-ethylhexanoate is applied since the ions of magnesium 2-ethylhexanoate 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 2-ethylhexanoate, data are available from studies for three trophic levels: algae, invertebrates and fish.

Read-across approach:

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of magnesium 2-ethylhexanoate in water (107.4 g/L at 20 °C), a complete dissociation of magnesium 2-ethylhexanoate resulting in magnesium 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 magnesium 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 magnesium to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as 2-ethylhexanoate 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 0.47, 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 2-ethylhexanoic acid of 4.72 results in:

log KML= 0.148 * 4.72 + 0.216

log KML= 0.915 (estimated magnesium-ethylhexanoate formation constant).

Thus, in the assessment of environmental toxicity and pathways of magnesium 2-ethylhexanoate, read-across to the assessment entities 2-ethylhexanoate and soluble magnesium substances is applied since the individual ions of magnesium 2-ethylhexanoate determine its environmental toxicity. Since magnesium ions and 2-ethylhexanoate ions behave differently in the environment regarding their toxicity, 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 magnesium 2-ethylhexanoate.

Conclusion on classification

Aquatic toxicity studies with magnesium 2-ethylhexanoate are not available, thus aquatic toxicity is addressed with existing data on the dissociation products. Magnesium is naturally ubiquitous in the environment. As magnesium is essential for normal physiological functioning in species of all trophic levels, e.g. as  body structure-forming element of bones or exoskeletons or elektrolyt in physiological liquids, it has a very low potential for toxicity to freshwater and saltwater organisms and adverse effects are lacking up to and including 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 ethylhexanoic acid are recalculated for magnesium 2 -ethylhexanoate based on a maximum ethylhexanoate content of 92.18 %.

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 53.5 mg/L, 92.6 mg/L and > 108.5 mg/L, respectively, and are well above the classification cut-off value for acute (short-term) aquatic hazard category 1. Therefore, magnesium 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 34.7 mg/L and 19.5 mg/L, respectively, and 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 > 108.5 mg/L, magnesium 2-ethylhexanoate does not classify as long-term aquatic hazard category 1 -3. Criteria for classification in category 4 are also not met. Therefore, magnesium 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.