Fatty acids, C8-10, zinc salts

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

23.8 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

178.6 µg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

2.38 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

PNEC marine water (intermittent releases):

17.9 µg/L

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

526.3 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.251 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.025 mg/kg sediment dw

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:

0.04 mg/kg soil dw

Extrapolation method:

equilibrium partitioning method

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read across statement:

 

Metal carboxylates are substances consisting of a metal cation and a carboxylic acid anion. Based on the water solubility of fatty acids, C8-10, zinc salts (338 mg/L at 20°C), a complete dissociation of fatty acids, C8-10, zinc salts resulting in zinc and fatty acids of an alkyl chain length from C8 to C10 may be assumed under environmental conditions upon contact with water. The respective dissociation is in principle 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, C8-10, zinc salts could not be identified. Data for zinc appear to be generally limited. However, zinc cations tend to form complexes with ionic character as a result of their low electronegativity. Further, the ionic bonding of zinc 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 zinc to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as fatty acids are not expected to bind strongly with zinc. Accordingly, protons will always out-compete zinc ions for complexation of monodentate ligands given equal activities of free zinc and hydrogen ions. The metal-ligand formation constants (log KML) of zinc with other carboxylic acids, i.e. acetic and benzoic acid, ranging from 0.56 to 1.59 (Bunting & Thong, 1969), further point to a low strength of the monodentate bond between carboxyl groups and zinc.

 

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 fatty acids (C8-10)* of 5.07 results in:

log KML= 0.301 * 5.07 + 0.015

log KML= 1.54 (estimated zinc-C8-10 fatty acid formation constant).

*Calculated as the mean pKa of octanoic acid (C8) and decanoic acid (C10)

 

Thus, it may reasonably be assumed that based on the estimated zinc-C8-10 fatty acid formation constant, the respective behaviour of the dissociated zinc cations and fatty acid anions in the environment determine the fate of Fatty acids, C8-10, zinc salts 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.

In order to evaluate the environmental fate of the Fatty acids, C8-10, zinc salts, information on the assessment entities zinc cations and representative fatty acid anions were considered. For a documentation and justification of that approach, please refer to the information given in the respective assessment entities and to the separate document attached to section 13, namely Read Across Assessment Report for Fatty acids, C8-10, zinc 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.

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

Conclusion on classification

FATTY ACIDS, C8-10, ZINC SALTS

Fatty acids, C8-10, zinc salts consists of fatty acid anions and zinc cations and is moderately soluble in water. For the conclusion on classification, aquatic toxicity data of Fatty acids, C8-10, zinc salts, and data for octanoic acid and decanoic acid and soluble zinc compounds are taken into account.

 

Based on available aquatic toxicity data of Fatty acids, C8-10, zinc salts, i.e. acute EL50 and chronic EL10 of 0.20 mg/L and 0.03 mg/L, respectively, for 72-h inhibition of growth rate of the algae P. subcapitata in standard test medium and considering its rapid degradability, the substance classifies Aquatic hazard, category Acute 1 (M-factor 1) and Chronic 2 according to Table 4.1.0 (a) and (b) (ii) of Regulation (EC) No 1272/2008.

 

In the assessment of the aquatic hazard potential of Fatty acids, C8-10, zinc salts, read-across to the assessment entities soluble zinc substances and C8-10 fatty acids is further applied since zinc cations and fatty acid anions determine its fate and toxicity in the environment. Please refer to the respective assessment entity for further details.

 

Acute (short-term) toxicity:

Acute toxicity data for the assessment entity “C8-10” are available for three trophic levels. The lowest L(E)C50 for fish, crustacean or algae is a 48-h EC50 of 15 mg /L observed for the algal species P. subcapitata. Thus, all EC50/LC50 values are well above the classification cut-off value for acute (short-term) aquatic hazard Category 1 of 1 mg/L according to Table 4.1.0 (a) of Regulation (EC) No 1272/2008.

 

Thus, the acute aquatic hazard classification is based on the more toxic moiety, i.e. the zinc cation, and acute ecotoxicity reference values of zinc are recalculated for Fatty acids, C8-10, zinc salts based on a maximum zinc content of 19 %. Fatty acids, C8-10, zinc salts would meet based on i) the acute aquatic ecotoxicity values of 136 µg Zn/L and 413 µg Zn/L for the zinc ion at pH 8 and pH 6 respectively; ii) the zinc content of Fatty acids, C8-10, zinc salts of 19 %, and iii) the resulting acute ecotoxicity reference value of 716 µg/L Fatty acids, C8-10, zinc salts at pH 8 as worst case, classification criteria of acute (short-term) aquatic hazard Category 1 with an acute M-factor 1 according to Table 4.1.0 (a) of Regulation (EC) No 1272/2008.

 

Chronic (long-term) toxicity:

Chronic toxicity data for the assessment entity “C8-10” are available for the three trophic levels. The lowest chronic NOEC/EC10 for fish, crustacean or algae is the 21-d NOEC of 200 µg/L decanoic acid observed for the crustacean Daphnia magna, resulting in a self-classification of C8-10 fatty acids as Aquatic Chronic 3 according to Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008. The self-classification of C8-10 fatty acids is in line with the respective harmonised classification of octanoic acid (CAS 124-07-2) and decanoic acid (C10, CAS 334-48-5) as Aquatic chronic 3 (Annex VI of Regulation (EC) 1272/2008). The 21-d NOEC of 200 µg/L decanoic acid used as ecotoxicity reference value would result in a chronic ecotoxicity reference value of 238.1 µg/L for Fatty acids, C8-10, zinc salts based on a maximum fatty acid content of 84 % meeting also classification criteria as Aquatic Chronic 3 according to Table 4.1.0 (b) (ii).

 

The lowest chronic aquatic ecotoxicity reference value for the assessment entity “Zinc” was observed for the algal species P. subcapitata (19 µg Zn/L) at neutral pH, which corresponds to a chronic ecotoxicity reference value of 100 µg/L for Fatty acids, C8-10, zinc salts based on a maximum zinc content of 19 %. The long-term (chronic) aquatic hazard classification is thus based on the most toxic moiety, i.e. the zinc cation. Fatty acids, C8-10, zinc salts would meet based on i) the lowest chronic aquatic ecotoxicity reference value observed for the algae Pseudokirchneriella subcapitata (19 µg Zn/L) at neutral pH; ii) the zinc content of Fatty acids, C8-10, zinc salts of 19 %, and iii) the resulting chronic ecotoxicity reference value of 100 µg/L for Fatty acids, C8-10, zinc salts, classification criteria of long-term aquatic hazard of Regulation (EC) No 1272/2008.

 

The chronic ecotoxicity reference value of 100 µg/L is compared with the criteria for long-term aquatic hazard classification, taking into account if zinc, the toxic moiety of concern, is considered rapidly degradable. The concept of “Degradability” was developed for organic substances and is not applicable to inorganic zinc substances. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” was developed to assess if a metal ion would remain present in the water column upon addition (and thus be able to exert a chronic effect) or would be rapidly removed from the water column. In this concept, “rapid removal” (defined as >70% removal within 28 days) is considered as equivalent to “rapidly degradable”. The rapid removal of zinc from the water column is documented in the section „Environmental fate“. Consequently, zinc is considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects. Based on the chronic ecotoxicity reference value of 100 µg/l, Fatty acids, C8-10, zinc salts would meet classification criteria of long-term aquatic hazard Category 2 in accordance with Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008.  

 

Altogether, based on reliable, adequate and relevant studies, including the substance-specific algae toxicity data according to OECD 201 and read-across to aquatic toxicity data of octanoic acid, decanoic acid, and soluble zinc substances, Fatty acids, C8-10, zinc salts meets classification criteria of Regulation (EC) No 1272/2008 as Acute (short-term) aquatic hazard Category 1 with an acute M-Factor of 1 and Chronic (long-term) aquatic hazard Category 2.