2-ethylhexanoic acid, copper salt

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

41.05 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

27.37 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

1.21 mg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

457.9 mg/kg sediment dw

Assessment factor:

1

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

3 557.9 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

342.1 mg/kg soil dw

Assessment factor:

1

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read-across:

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the solubility of 2-ethylhexanoic acid, copper salt in water, a complete dissociation of 2-ethylhexanoic acid, copper salt resulting in copper and 2-ethylhexanoate 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 2-ethylhexanoic acid, copper salt 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 2-ethylhexanoate 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 1-6 -1.92, respectively (Bunting and Thong, 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 2-ethylhexanoic acid of 4.72 results in:

log KML= 0.430 * 4.72 + 0.213

log KML= 2.24 (estimated copper-ethylhexanoate formation constant).

Thus, in the assessment of environmental toxicity of 2-ethylhexanoic acid, copper salt, read-across to the assessment entities 2-ethylhexanoate and soluble copper substances is applied since the individual ions of 2-ethylhexanoic acid, copper salt determine its environmental toxicity. Since copper ions and 2-ethylhexanoate 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 2-ethylhexanoic acid, copper salt.

 

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.

Carbonaro & Di Toro (2007):Linear free energy relationships for metal ligand complexation: Monodentate binding to negatively-charged oxygen donor atoms. GCA 71, p3958-3968.

Conclusion on classification

Aquatic toxicity studies of 2-ethylhexanoic acid, copper salt are not available. Thus, read-across to the assessment entities soluble copper substances and 2-ethylhexanoic acid is applied since the ions of 2-ethylhexanoic acid, copper salt determine its fate and toxicity in the environment. Reliable data available for soluble copper substances and 2 -ethylhexanoate indicate that the moiety of ecotoxicological concern are copper cations. Thus, the aquatic hazard assessment is based on the toxic moiety, i.e. copper cations, and acute and chronic ecotoxicity reference values of copper are recalculated for 2-ethylhexanoic acid, copper salt based on a maximum copper content of 19 %.

Acute (short-term aquatic) hazard:

Based on the lowest identified acute ecotoxicity reference value of 12.1 µg Cu/L for copper ions at pH 6 and a maximum copper content of 2-ethylhexanoic acid, copper salt of 19 %, the acute ecotoxicity reference value recalculated for 2-ethylhexanoic acid, copper salt amounts to 63.68 µg/L 2-ethylhexanoic acid, copper salt. Therefore, 2-ethylhexanoic acid, copper salt meets classification criteria of acute (short-term) aquatic hazard Category 1 of Regulation (EC) No 1272/2008 with an acute M-Factor of 10.

Long-term (chronic) aquatic hazard:

Based on the lowest identified chronic ecotoxicity reference value of 12 µg Cu/L for copper ions at pH 7 and a maximum copper content of 2-ethylhexanoic acid, copper salt of 19 %, the chronic ERV recalculated for 2-ethylhexanoic acid, copper salt amounts to 63.16 µg/L 2-ethylhexanoic acid, copper salt. The chronic ecotoxicity reference value of 63.16 µg/L is compared to criteria for long-term aquatic hazard classification according to Regulation (EC) 1272/2008, taking into account that copper ions are removed from the water column. Based on available evidence (please refer to the attached detailed reports on environmental hazard classification of copper), more than 70% of dissolved copper is removed within 28 days and transformed into stable sulfide complexes (Cu-S) under most “environmentally relevant” conditions. Remobilisation of Cu into the water-column is not likely. Copper is therefore considered rapidly removeable (i.e. equivalent to “rapid degradation” for organic substances). 2 -ethylhexanoate anions are also readily biodegradable.

Based on the chronic ecotoxicity reference value of 63.16 µg/l, 2-ethylhexanoic acid, copper salt meets classification criteria of long-term aquatic hazard Category 2 in accordance with Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008.

Thus, 2-ethylhexanoic acid, copper salt meets classification criteria of acute aquatic hazard Category 1 (M-factor 10) and long-term aquatic hazard Category 2 according to Regulation (EC) No 1272/2008 and subsequent adaptations.