Manganese neodecanoate

Endpoint summary

Description of key information

The fate of manganese neodecanoate in the environment is most accurately evaluated by separately assessing the fate of its moieties manganese cations and neodecanoate anions. Since manganese cations and neodecanoate 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.

Manganese cations: Abiotic and biotic degradation are not relevant and not expected to affect the fate of manganese cations in the environment. A 100-d adsorption / desorption study of manganese (2+) cations in 35 soils according to OECD 106 indicates that sorption is pH sensitive, and a median Kd value of 1355 L/kg was determined (pH range 3.0-8.5. Regarding Mn partitioning in sediments and suspended matter, a logKp(solids-water in sediment) and logKp(solids-water in suspended matter) of 4.57 and 3.78 were derived based on several European field studies, respectively. Manganese as an essential trace nutrient in animals and plants is actively regulated in organisms and not expected to bioaccumulate.

 

Neodecanoic 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.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 Koc of neodecanoic acid 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.

According to a bioconcentration study in fish, neodecanoic acid appears to have a low potential to bioaccumulate (BCF < 225 L/kg wwt fish).

Additional information

Read-across approach:

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of manganese neodecanoate in water, a dissociation resulting in manganese 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 manganese neodecanoate could not be identified. According to the Irving-Williams series, stability constants formed by divalent first-row transition metal ions such as manganese are relatively low compared to other transition metals (Mn(II) < Fe(II) < Co(II) < Ni(II) < Cu(II) > Zn(II)).Further, based on an analysis by Carbonaro et al. (2007) of monodentate binding of manganese to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as fatty acid anions are not expected to bind strongly with manganese. 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 neodecanoic acid of 4.69 results in:

log KML = 0.225 * 4.69 + 0.283

log KML = 1.34 (estimated manganese-neodecanoate formation constant).

Thus, it may reasonably be assumed that based on the estimated manganese-neodecanoate formation constant, the respective behaviour of the dissociated manganese cations and neodecanoate anions in the environment determine the fate of manganese neodecanoate 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 manganese neodecanoate, read-across to neodecanoate and soluble manganese substances is applied since the individual ions of manganese neodecanoate determine its environmental fate. Since manganese 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.

In order to evaluate the environmental fate and toxicity of the substance manganese neodecanoate, information on the assessment entities manganese cations and neodecanoate 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 manganese neodecanoate.

 

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.

Bunting JW & Thong KM (1969) Stability constants for some 1:1 metal-carboxylate complexes. Canadian Journal of Chemistry, 48, 1654.