Barium dibenzoate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

302.6 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

531.3 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1 578.9 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

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:

PNEC soil

PNEC value:

546.6 mg/kg soil dw

Assessment factor:

2

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

The fate and toxicity of barium dibenzoate in the environment is most accurately evaluated by separately assessing the fate of its moieties barium and benzoate.

 

Barium dibenzoate dissolves and dissociates into barium and benzoate ions upon contact with an aqueous medium. Therefore, the aquatic hazard potential is assessed based on the toxicity data available for the assessment entities barium and benzoate ions since the ions of barium dibenzoate determine its environmental fate and toxicity.

Acute (short-term) toxicity data: EC/LC50 values of 3 trophic levels (algae, invertebrates and fish) range for barium from > 1.15 mg Ba/L to 14.5 mg Ba/L and and for benzoic acid from 33.1 mg/L benzoic acid to > 100 mg/L benzoic acid.

Chronic (long-term) toxicity: NOEC/EC10 values of 3 trophic levels (algae, invertebrates and fish) range from ≥ 1.15 mg Ba/L to 2.9 mg Ba/L and for benzoic acid from 3.4 mg/L benzoic acid to 120 mg/L benzoic acid.

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, 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 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 fate 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.

Conclusion on classification

The fate and toxicity of barium dibenzoate in the environment is most accurately evaluated by separately assessing the fate of its moieties barium and benzoate.

 

Acute (short-term) toxicity data: EC/LC50 values of 3 trophic levels (algae, invertebrates and fish) range for barium from > 1.15 mg Ba/L to 14.5 mg Ba/L and for benzoic acid from 33.1 mg/L benzoic acid to > 100 mg/L benzoic acid. Thus, all EC50/LC50 values are well above the classification cut-off value for acute (short-term) aquatic hazard category 1 of 1 mg/L. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (a), classification for acute (short-term) aquatic hazard is not required for barium dibenzoate.

Chronic (long-term) toxicity: NOEC/EC10 values of 3 trophic levels (algae, invertebrates and fish) range from ≥ 1.15 mg Ba/L to 2.9 mg Ba/L and for benzoic acid from 3.4 mg/L benzoic acid to 120 mg/L benzoic acid. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (b), classification for long-term aquatic hazard is not required for barium dibenzoate since all chronic EC10/NOEC values are above the classification cut-off of 1 mg/L.