Barium m-toluate

Endpoint summary

Description of key information

The fate of barium m-toluate in the environment is most accurately evaluated by separately assessing the fate of its moieties barium and m-toluate. Since barium cations and m-toluate anions behave differently in the environment, including processes such as stability, degradation, transport and distribution, a separate assessment of the environmental fate of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity.

 

Barium does not contain hydrolysable groups. Further, biotic degradation is not relevant for inorganic substances such as barium. The coefficient for partitioning of barium between particulate matter and water (Kpsusp) of 5,217 L/Kg was derived for EU waters whereas the Kp for the distribution between sediment and water (Kpsed) was estimated with 3,478 L/kg. For soil, a solid-water partitioning coefficient of 60.3 L/kg was determined experimentally.

m-Toluate is ready biodegradable and has a log Kow of ~2.4. Thus, abiotic degradation and adsorption to soil, sediments or suspended matter are not expected to affect the fate of m-toluate in the environment. Based on the log Kow, m-toluate is not expected to bioaccumulate.

Additional information

Read-across

 

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion.Based on the solubility of barium m-toluate in water (35.7 g/L at pH 5.63), a complete dissociation of barium m-toluate resulting in barium cations and m-toluate 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 barium m-toluate could not be identified. Data for barium appear to be generally limited. However, barium cations tend to form complexes with ionic character as a result of their low electronegativity. Further, the ionic bonding of barium 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 et al. (2011) of monodentate binding of barium to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as m-toluate anions are not expected to bind strongly with barium.

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 m-toluic acid of 4.25 results in:

log KML= 0.186 * 4.25 – 0.171

log KML= 0.62 (estimated barium m-toluate formation constant).

 

Thus, it may reasonably be assumed that based on the estimated barium-toluate formation constant, the respective behaviour of the dissociated barium cations and m-toluate anions in the environment determine the fate of barium m-toluate 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 fate of barium m-toluate, read-across to m-toluate and soluble barium substances is applied since the individual ions of barium m-toluate determine its environmental fate. Since barium ions and m-toluate 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 barium m-toluate, information on the assessment entities barium cations and m-toluate 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 barium-m-toluate.

 

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.