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The fate of fatty acids, C9 -13-neo, copper salts in the environment is most accurately evaluated by separately assessing the fate of its constituents copper cations and fatty acids, C9 -13-neo anions. For the fatty acid anions, read-across to neodecanoic acid (as structural analogue of fatty acids, C6-13-neo) is applied in accordance with the U.S. EPA HPV programme for C5-C28 neo acids (U.S. EPA, 2009). Please refer to the section for the respective assessment entity.

Copper

Abiotic degradation including hydrolysis or phototransformation in water, soil or air, is not relevant for inorganic substances including copper ions. In general, (abiotic) degradation is irrelevant for inorganic substances that are assessed on an elemental basis.

Biotic degradation is not relevant for metals and metal compounds. Copper as an element is not considered to be (bio)degradable but is removed from the water column.Copper is therefore considered rapidly removed, conceptually equivalent to “rapid degradation” for organic substances.

Transport and distribution: Copper adsorption is quantified by the log Kp (soil/porewater) = 3.33; log Kp(sediment/freshwater) = 4.39 and the log Kp (suspended matter/freshwater) = 4.48, rendering it mostly immobile in the different environmental compartments.

Fatty acids, C9 -13-neo anions (and its structural analogue neodecanoic acid):

Abiotic degradation: Abiotic degradation is not relevant for fatty acids, C9 -13-neo anions since they do not contain any components that can hydrolyse in water at an environmentally relevant pH.

Biotic degradation: Neodecanoic acid is not readily biodegradable (11% biodegradation in 28 days) based on a standard OECD test.

Bioaccumulation: According to a bioconcentration study, neodecanoic acid has a low potential to bioaccumulate (BCF < 225 L/kg wwt fish).

Transport and distribution: The estimated logKoc of neodecanoic acid is 2.08 (Koc = 121 L/kg) 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 to remain largely in water.

Additional information

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of fatty acids, C9-13-neo, copper salts in water, a complete dissociation of fatty acids, C9-13-neo, copper salts resulting in copper cations and fatty acids, C9-13-neo 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, C9-13-neo, copper salts could not be identified. According to the Irving-Williams series, stability constants formed by divalent first-row transition metal ions generally increase to a maximum stability of copper (Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II)). However, based on an analysis by Carbonaro et al. (2011) of monodentate binding of copper to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as fatty acids, C9-13-neo anions are not expected to bind strongly with copper, especially when compared to polydentate (chelating) ligands. The metal-ligand formation constants (log KML) of copper with other carboxylic acids, i.e. butyric acid and benzoic acid amount to log KML values of 2.14 and 1.51 -1.92, respectively (Bunting and Thong, 1970; CRC, 1972) and point to a moderately stable complexation. 

 

 

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, C9-13-neo acid of 5.05 (QSAR estimate of MarvinSketch V.5.3.8) results in: log KML= 0.430 * 5.05 + 0.213 log KML= 2.38 (estimated copper- fatty acids, C9-13-neo formation constant).

Thus, in the assessment of environmental fate and pathways of fatty acids, C9-13-neo, copper salts, read-across to the assessment entities soluble copper substances and fatty acids, C9-13-neo (and its structural anaologue neodecanoic acid in accordance with the U.S. EPA HPV programme for C5-C28 neo acids (U.S. EPA, 2009, HPV Chemicals, Neoacids C5-C28 Category), is applied since the ions of fatty acids, C9-13-neo, copper salts determine its environmental fate. Since copper ions and fatty acids, C9-13-neo 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. 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, C9-13-neo, copper 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.

CRC Handbook of Food Additives, 2nd ed. 1972. Butyric acid-copper formation constant.

Bunting, J. W., & Thong, K. M. (1970). Stability constants for some 1: 1 metal–carboxylate complexes. Canadian Journal of Chemistry, 48(11), 1654-1656.