Registration Dossier
Registration Dossier
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EC number: 208-551-0 | CAS number: 533-00-6
Endpoint summary
Administrative data
Description of key information
The fate of barium dibenzoate in the environment can be most accurately evaluated by separate assessment of the fate of the cation barium and the anion benzoate.
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.
Benzoate is ready biodegradable and has a log Kow of 1.87. Thus, abiotioc degradation and adsorption to soil, sediments or suspended matter are not expected to affect the fate of benzoate in the environment. However, some phototransformation may be possible in water, and the Koc calculated from Kow is 15.49 according to QSAR-based estimates of KOCWIN. Based on the log Kow, benzoate is not expected to bioaccumulate.
Additional information
Read-across
Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Barium dibenzoate is very soluble according to the water solubility test (OECD TG 105). Thus, a complete dissociation of barium dibenzoate resulting in barium cations and m-toluate anions 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 barium dibenzoate could not be identified. Data for barium appear to be generally limited. However, barium 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 benzoate 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 benzoic acid of 4.3 results in:
log KML= 0.186 * 4.3 – 0.171
log KML= 0.63 (estimated barium-dibenzoate formation constant).
Thus, it may reasonably be assumed that based on the estimated barium-dibenzoate formation constant, the respective behaviour of the dissociated barium cations and benzoate anions in the environment determine the fate of barium dibenzoate upon dissolution with regard to (bio)degradation, bioaccumulation and 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 barium dibenzoate, read-across to benzoate and soluble barium substances is applied since the individual ions of barium dibenzoate determine its environmental fate. Since barium cations and benzoate anions 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 toxicity of the substance barium dibenzoate, information on the assessment entities barium cations and benzoate 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-dibenzoate.
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.
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