Barium 3,5,5-trimethylhexanoate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

379.5 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

68.6 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1 980.2 mg/kg sediment dw

Assessment factor:

1

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:

685.5 mg/kg soil dw

Assessment factor:

2

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.024 g/kg food

Assessment factor:

90

Additional information

The fate and toxicity of barium3,5,5 -trimethylhexanoatein the environment is most accurately evaluated by separately assessing the fate of its constituents barium andtrimethylhexanoate.

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion.Based on its water solubility, barium 3,5,5 -trimethylhexanoate is expected to dissociate completely under environmental conditions resulting in barium and trimethylhexanoate 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.

 

A metal-ligand complexation constant of barium 3,5,5-trimetylhexanoate could not be identified. Data for barium appear to be generally limited. However, barium tends 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. (2007) of monodentate binding of barium to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as trimethylhexanoate 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 3,5,5-trimethylhexanoic acid of 5.23 results in:

log KML= 0.186 * 5.23 – 0.171

log KML= 0.80 (estimated barium-trimethylhexanoate formation constant).

 

Thus, it may reasonably be assumed that based on the estimated barium- trimethylhexanoate formation constant, the respective behaviour of the dissociated barium cations and trimethylhexanoate anions in the environment determine the fate of barium 3,5,5-trimethylhexanoate 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.

 

In the assessment of environmental fate and toxicity of barium 3,5,5-trimethylhexanoate, read-across to the assessment entities soluble barium substances and 3,5,5-trimetylhexanoic acid (and its structural analogue neodecanoic acid) is applied since the ions of barium 3,5,5-trimethylhexanoate determine its environmental fate. Since barium cations and trimethylhexanoate 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.

 

In order to evaluate the environmental fate and toxicity of barium 3,5,5-trimethylhexanoate, information on the assessment entities barium cations and trimethylhexanoate 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 3,5,5-trimethylhexanoate.

 

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

Aquatic toxicity studies are not available for barium 3,5,5-trimethylhexanoate. Read-across to the assessment entities soluble barium substances and trimethylhexanoic acid (and its structural analogue neodecanoic acid) is applied for the assessment of barium 3,5,5-trimethylhexanoate since the ions of barium 3,5,5-trimethylhexanoate determine its fate and toxicity in the environment.

Acute (short-term) toxicity: 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 are > 100 mg/L for neodecanoic acid (the structural analogue of trimethylhexanoate). The low toxic potential of the latter is confirmed by QSAR-based estimations for its structural analogue trimethylhexanoic acid. According to the QSAR-based outcome of the model ECOSAR v.2.0, trimethylhexanoic acid has also a low potential for acute toxicity since the 48-h EC/LC50 values were estimated with 65.0, 52.3 and 81.4 mg/L for freshwater algae, daphnids and fish, respectively. 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 3,5,5-trimethylhexanoate.

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.

Regarding the aquatic toxicity of neodecanoic acid (structural analogue of trimethylhexanoate), reliable data are available for invertebrates and fish. The respective NOEC/EC10 values are > 1 mg/L and indicate a low potential for chronic toxicity. Regarding algae, an EC10 or NOEC is not available for neodecanoate. However, based on the fact that the EC50 for growth rate of algae is > 100 mg/L, we may assume that it is unlikely that the EC10/NOEC < 1 mg/L. The low potential for chronic toxicity is supported by QSAR-based estimates for trimethylhexanoic acid. According to the QSAR-based outcome of the model ECOSAR v.2.0, trimethylhexanoic acid has also a low potential for toxicity since chronic effect values ChV (ChV = 10^([log (LOEC x NOEC)]/2)) were estimated with 22.4, 7,2 and 9.2 mg/L for freshwater algae, daphnids and fish, respectively. Thus, EC10/NOEC values of trimethylhexanoate and its structural analogue neodecanoate are well above the classification cut-off value for (chronic) long-term aquatic hazard of 1 mg/L. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (b), classification for long-term aquatic hazard is not required for barium 3,5,5-trimethylhexanoate.