Fatty acids, C9-13-neo-, barium salts

Endpoint summary

Description of key information

The fate of fatty acids, C9 -13 neo, barium salts in the environment is most accurately evaluated by separately assessing the fate of its moieties barium and fatty acids, C9 -13 neo or rather its structural analogue neodecanoic acid.In the assessment of environmental fate and behaviour of fatty acids, C9 -13 neo, barium salts, data available for the barium cation and the neodecanoate anion indicate that abiotic and biotic degradation in respective compartments do not contribute significantly to its fate in the environment.

 

Barium does not contain hydrolysable groups. Further, biotic degradation are 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.

Neodecaoic acid: Abiotic degradation is not considered to significantly affect the environmental fate of neodecanoic acid since neodecanoic acid is lacking hydrolysable functional groups and does not absorb light within a range of 290 to 750 nm.

Biotic degradation: Neodecanoic acid is not readily biodegradable (11% biodegradation in 28 d) based on results from a standard OECD ready biodegradation test. Studies are not available to assess the biodegradability of neodecanoic acid under simulated conditions or in soil, but given the limited biodegradation in water, biodegradation under simulated conditions, or in soil is not expected to occur to a great extent.

Transport and distribution: The estimated neo-decanoic acid Koc is 121 and may be sensitive to pH. The vapor pressure is very low, i.e. 0.65 Pa suggesting a limited volatilization from soil. Henry’s Law constant for neo-decanoic acid is calculated with 0.54 Pa-m3/mole at 25 °C indicating that volatilization from water is not expected to occur at a rapid rate, but may occur. Neodecanoic acid is a weak organic acid with an estimated dissociation constant (pKa) of 4.69. Consequently, neodecanoic acid, at neutral pH, typical of most natural surface waters, is expected to dissociate to the ionised form and therefore to remain largely in water.

Additional information

Read-across

 

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of fatty acids, C9 -13 neo, potassium salts in water, a complete dissociation resulting in potassium cations and neodecanoate 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 fatty acids, C9-C13-neo, barium salts 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 fatty acids, C9-C13-neo 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 mean pKa of fatty acids, C9-C13-neo of 5.05 results in:

log KML= 0.186 * 5.05 - 0.171

log KML= 0.77 (estimated barium-fatty acids, C9-C13-neo formation constant).

 

Thus, it may reasonably be assumed that based on the estimated barium-fatty acids, C9-C13-neo formation constant, the respective behaviour of the dissociated barium cations and fatty acids, C9-C13-neo anions in the environment determine the fate of fatty acids, C9-C13-neo, barium salts 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 fate and pathways of fatty acids, C9-C13-neo, barium salts, read-across to soluble barium substances and neodecanoic acid (structural analogue of fatty acids, C9-C13-neo) is applied since individual ions of fatty acids, C9-C13-neo, barium salts determine its environmental fate. Since barium cations and fatty acids, C9-C13-neo 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 and toxicity of the substance fatty acids, C9-C13-neo, barium salts information on the assessment entities barium cations and neodecanoic acid (structural analogue of fatty acids, C9-C13-neo) 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 fatty acids, C9-C13-neo, barium salts.

 

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.