Zinc dimyristate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

158.5 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

46.9 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

769.2 µg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

906.2 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

434.6 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:

273.8 mg/kg soil dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Metal carboxylates are salts consisting of metal cation and carboxylic acid anion. Based on the solubility of zinc ditetradecanoate in water, a complete dissociation resulting in zinc and tetradecanoate ions may be assumed under environmental conditions. 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.

However, under environmental conditions, a reunion of the dissociated ions is highly unlikely and it may reasonable be assumed that the respective behaviour of the dissociated zinc cations and tetradecanoate anions in the environment determine the fate of zinc ditetradecanoate 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 the (eco)toxicological potential.

A metal-ligand complexation constant of zinc ditetradecanoate could not be identified. Data for zinc appear to be generally limited. However, zinc ions 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. (2007) of monodentate binding of zinc to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as tetradecanoate anions 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 Irving–Rossotti slope and intercept, respectively. Applying the equation and parameters derived by Carbonaro & Di Toro (2007) and the pKa of tetradecanoic acid of 4.90 results in:

log KML = 0.301 * 4.90 + 0.015

log KML = 1.49 (estimated zinc- tetradecanoate formation constant).

Thus, it may reasonably be assumed that based on the zinc ditetradecanoate formation constant the respective behaviour of the dissociated zinc cations andtetradecanoateanions in the environment determines the fate of zinc ditetradecanoate upon dissolution. In the assessment of environmental fate and toxicity of zinc ditetradecanoate, read-across to analogue substances and/or the assessment entities soluble zinc substances and tetradecanoic acid is applied since the ions of zinc ditetradecanoate determine the environmental fate and toxicity of zinc ditetradecanoate. Since zinc ions and tetradecanoate ions behave differently in the environment, a separate assessment of the environmental fate and toxicity 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 zinc ditetradecanoate.

Conclusion on classification

Zinc ditetradecanoate is slightly soluble in water (water solubility limit of 1.14 mg/L), and thus its bioavailability in environmental compartments is expected to be low. The ecotoxicity data available for analogue substances indicate that the acute aquatic toxicity of zinc salts of shorter- and longer chained (C12-C18) fatty acids to algae, daphnia and fish is above the water solubility limit:

Algae: Based on a reliable study with the analogue substance zinc dilaurate (zinc salt of a C12-fatty acid), the EL10 and EL50 amount to 3.73 mg/L and 12.87 mg/L WAF for the acute toxicity to freshwater algae (Pseudokirchneriella subcapitata), respectively. The toxicity of a longer-chained (C16-18) to Pseudokirchneriella subcapitata is also low (EL10= 3.31 mg/L WAF, EL50 > 100 mg/L WAF fatty acids, C16-18, zinc salts). Thus, zinc salts of shorter- and longer-chained fatty acids appear to have a low potential for toxicity to freshwater algae. A similar low potential is assumed for zinc ditetradecanoate.

Crustacea: The EC50 values for the acute toxicity of the analogue substances zinc dilaurate (zinc salt of a C12-fatty acid) and Fatty acids, C16-18, zinc salts to Daphnia magna are > 10 mg/L and > 100 mg/L, respectively, and thus above the water solubility limit of zinc ditetradecanoate of 1.14 mg/L. Thus, zinc salts of shorter- and longer-chained fatty acids appear to have a low potential for acute toxicity to freshwater invertebrates. A similar low potential is assumed for zinc ditetradecanoate.

Fish: The EC50 values for the acute toxicity of the analogue substances zinc dilaurate (zinc salt of a C12-fatty acid) and Fatty acids, C16-18, zinc salts to Danio rerio are > 10 mg/L and > 10,000 mg/L, respectively, and thus above the water solubility limit of zinc ditetradecanoate of 1.14 mg/L. Thus, zinc salts of shorter- and longer-chained fatty acids appear to have a low potential for acute toxicity to freshwater fish. A similar low potential is assumed for zinc ditetradecanoate.

Thus, zinc salts of shorter- and longer-chained (C12-C18) fatty acids appear to have a low potential for acute toxicity to freshwater algae, invertebrates and fish. A similar low potential is assumed for zinc ditetradecanoate.

Based on studies of zinc salts of shorter- and longer-chained (C12-C18) fatty acids, i.e. analogue substances, in which the acute toxicity to algae, Daphnia and fish is above 1 mg/L, zinc ditetradecanoate does not meet acute (short-term) aquatic hazard criteria of Regulation (EC) No 1272/2008.

The acute toxicity data further indicate that zinc salts of shorter- and longer-chained (C12-C18) fatty acids have a significantly lower aquatic toxicity than soluble zinc salts. It is therefore assumed that a high fraction of zinc from zinc salts of medium- and longer chained (C12-C18) fatty acids is not bioavailable.

Based on the hazard assessment of "Zinc" within the framework of Regulation (EC) No 1907/2006, ecotoxicity reference values for the zinc ion are:

Acute

-for low pH: 0.413 mg Zn/L (based on single lowest value for Ceriodaphnia dubia)

-for the neutral/high pH: 0.136 mg Zn/L (based on single lowest value for Pseudokirchneriella subcapitata)

Chronic

-for low pH: 0.082 mg Zn/L (Daphnia magna)

-for the neutral/high pH:8.0: 0.019 mg Zn/L (Pseudokirchneriella subcapitata)

Thus, algae appear to be the most sensitive trophic level with regard to toxicity of zinc.

Zinc ditetradecanoate 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 maximum zinc content of zinc ditetradecanoate of 13 %, and iii) the resulting acute ecotoxicity reference value of 1046.2 µg/L zinc ditetradecanoate at pH 8 as worst case, does also not meet classification criteria of acute (short-term) aquatic hazard Category 1 of Regulation (EC) No 1272/2008.

Zinc ditetradecanoate would however meet based on i) the lowest chronic aquatic ecotoxicity reference value observed for the algae Pseudokircherniella subcapitata (19 µg Zn/L) at neutral pH; ii) the maximum zinc content of zinc ditetradecanoate of 13 %, and iii) the resulting chronic ecotoxicity reference value of 146.2 µg/L zinc ditetradecanoate as worst case, classification criteria of long-term aquatic hazard of Regulation (EC) No 1272/2008. However, based on toxicity scores of the trophic level most sensitive to zinc, i.e. EL10 value (3.73 mg/L) for the alga P. subcapitata, the analogue substance zinc dilaurate (with a zinc content of 14%) and by read-across zinc ditetradecanoate (with a maximum zinc content of 13 %) does not require classification for long-term aquatic hazard.

In addition, the moieties of zinc ditetradecanoate are readily biodegradable (based on read-across of ready biodegradability observed for zinc salts of shorter-chained (C8) and longer-chained (C16-18) fatty acids in OECD 301 studies) or are removed from the water column. 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. 

The moieties of zinc ditetradecanoate are also not expected to bioaccumulate: bioaccumulation is not relevant for essential elements such as zinc due to homeostatic control mechanisms and fatty acids degrade by the ß-oxidation pathway.

It is therefore concluded that based on(i)studies of zinc salts of shorter- and longer-chained (C12-C18) fatty acids, i.e. analogue substances, in which the acute toxicity to algae, Daphnia and fish is above 1 mg/L, (ii) moieties of zinc tetradecanoate being readily biodegradable or removed from the water column, (iii) moieties of zinc tetradecanoate being not bioaccumulative, and (iv) the EL10 of 3.73 mg/L of an analogue substance for algae, does not require classificationaslong-term aquatic hazard in accordance with Figure 4.1.1 and Table 4.1.0 (b)(ii) and (iii) of Regulation (EC) No 1272/2008.

In sum, zinc ditetradecanoate does not meet classification criteria of acute (short-term) and long-term aquatic hazard of Regulation (EC) No 1272/2008.

This conclusion is consistent with the conclusions from the EU risk assessment for the analogue substance zinc distearate conducted within the framework of EU Existing Chemicals Regulation (EEC) No 793/93 (Final report R074_0805_env, May 2008): "Zinc distearate is not classified for the environment."