Cerium(3+) neodecanoate

Endpoint summary

Description of key information

The fate of cerium neodecanoate in the environment is most accurately evaluated by separately assessing the fate of its constituents cerium cations and neodecanoate anions.

Cerium:

Biotic degradation is not relevant for inorganic substances, including metals. Cerium as an element is not considered to be (bio)degradable.

Neodecanoic acid: Neodecanoic acid is not readily biodegradable (11% biodegradation in 28 d) based on results from a standard OECD ready biodegradation test.

Additional information

Read-across

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. In a water solubility test according to OECD TG 105, a solubility of 157 µg/L cerium neodecanoate was determined. Thus, cerium neodecanoate is expected to dissociate in environmental media resulting in cerium and neodecanoate ions. 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. Based on an analysis by Carbonaro et al. (2007) of monodentate binding of cerium to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as neodecanoate anions are not expected to bind strongly with cerium.

 

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 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= 0.356 * 4.69 + 0.739

log KML= 2.41 (estimated cerium-neodecanoate formation constant).

 

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

 

In the assessment of environmental toxicity of cerium neodecanoate, read-across to the assessment entities soluble cerium substances and neodecanoic acid is applied since the ions of cerium neodecanoate determine its ecotoxicologic potential. Since cerium cations and neodecanoate anions behave differently in the environment, including processes such as stability, degradation, transport and distribution, 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 cerium neodecanoate, information on the assessment entities cerium cations and neodecanoate anions 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 cerium 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.