Barium m-toluate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

350 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

28.8 µg/L

Assessment factor:

500

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

80.33 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1 823.7 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:

631.3 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 m-toluate in the environment is most accurately evaluated by separately assessing the fate of its moieties barium and m-toluate.

 

Barium m-toluate dissolves and dissociates into barium and m-toluate 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 m-toluate ions since the ions of barium m-toluate 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 for m-toluate from 17.87 mg/L to 81.4 mg/L m-toluate.

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. For m-toluate, NOEC/EC10 values of 2 trophic levels (algae and invertebrates) range from 9.63 mg/L to 9.93 mg/L m-toluate.

Read-across

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.

 

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 toxicity 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 toxicity of the substance barium m-toluate, information on the assessment entities barium cation and m-toluate anion 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.

Conclusion on classification

The fate and toxicity of barium m-toluate in the environment is most accurately evaluated by separately assessing the fate of its moieties barium and m-toluate. Barium m-toluate dissolves and dissociates into barium and m-toluate 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 m-toluate ions since the ions of barium m-toluate 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 for m-toluate from 17.87 mg/L to 81.40 mg/L m-toluate. 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 m-toluate.

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. For m-toluate, NOEC/EC10 values of 2 trophic levels (algae and invertebrates) range from 9.63 mg/L to 9.93 mg/L m-toluate. According to the QSAR-based outcome of the model ECOSAR v.2.0, m-toluate has a very low potential for chronic toxicity to freshwater and saltwater fish with respective chronic values (ChV = 10^([log (LOEC x NOEC)]/2)) well above 10 mg/L. In accordance with Regulation (EC) No 1272/2008, classification for chronic aquatic hazard is not required for barium m-toluate as all chronic EC10/NOEC values are above the classification criteria of 1 mg/L. Based on the surrogate approach (Table 4.1.0 (b) (iii), m-toluate would also not meet chronic classification criteria since m-toluate is rapidly biodegradable and the log Kow is well below 4. In accordance with Regulation (EC) No 1272/2008, classification for chronic aquatic hazard is not required for barium m-toluate.Criteria for the "Safety net" classification in Category Chronic 4 are also not met.

Therefore, Barium m-toluate does not meet classification criteria as acute (short-term) and long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008.