Copper(2+) neodecanoate

Endpoint summary

Description of key information

The fate of copper (2+) neodecanoate in the environment is most accurately evaluated by separately assessing the fate of its moieties copper cations and neodecanoate anions. In the assessment of environmental fate and behaviour of copper (2+) neodecanoate data available for copper cations and neodecanoate anions indicate that abiotic degradation in respective compartments does not contribute significantly to its fate in the environment:

 

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.

Neodecanoic acid

Abiotic degradation: Abiotic degradation is not relevant for neodecanoic acid since it does not contain any components that can hydrolyse in water at environmentally relevant pH.

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

Bioaccumulation: According to a bioconcentration study, neodecanoic acid exhibits 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. Thevapor 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 copper (2+) neodecanoate in water, a complete dissociation of copper (2+) neodecanoate resulting in copper and neodecanoate ions 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 Copper (2+) neodecanoate 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 & Di Toro (2007) of monodentate binding of copper to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as neodecanoate 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 Irving–Rossotti slope and intercept, respectively. Applying the equation and parameters derived by Carbonaro & Di Toro (2007) and the pKa of neodecanoic acid of 4.69 results in:

log KML= 0.430 * 4.69 + 0.213

log KML= 2.23 (estimated copper- neodecanoate formation constant).

Thus, in the assessment of environmental fate and pathways of copper (2+) neodecanoate, read-across to the assessment entities soluble copper substances and neodecanoate is applied since the individual ions of copper (2+) neodecanoate determine its environmental fate. Since copper ions and neodecanoate 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 copper (2+) neodecanoate.

Reference:

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

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.