Hexanoic acid, 2-ethyl-, zinc salt, basic

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

89.6 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

26.5 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

226 µg/L

Assessment factor:

100

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

8.17 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.817 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:

1.36 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 approach

In the assessment of the ecotoxicity of hexanoic acid, 2-ethyl-, zinc salt, basic, a read-across approach from data for the metal cation and the organic anion is followed. This read-across strategy is based upon the assumption that upon release to the environment and dissolution in aqueous media, hexanoic acid, 2-ethyl-, zinc salt, basic will dissociate and only be present in its dissociated form, i.e. as zinc cation and 2-ethyl hexanoate anion.

Upon dissolution in water, it is indeed predicted that metal carboxylates dissociate completely into the metal cation and the organic anion at environmentally relevant conditions. No information is available on the stability constants of hexanoic acid, 2-ethyl-, zinc salt, basic, but predictions of stability of other zinc carboxylates (Zn propionate, Zn valerate, Zn isovalerate and Zn benzoate) in a standard ISO 6341 medium (2 mMCaCl₂, 0.5 mM MgSO₄, 0.77 mM NaHCO₃ and 0.077 mM KCl, pH 6 and 8) clearly show that monodentate ligands such as carboxylic acids have no potential for complexing zinc ions in solution (Visual minteq. Version 3.0, update of 18 October 2012. http://www2.lwr.kth.se/English/OurSoftware/vminteq/index.html).

The fate and behaviour (e.g. partitioning) in the environment for Zn²⁺ and 2-ethyl hexanoate anion are predicted to be significantly different from each other, resulting in a different distribution over the environmental compartments (water, air, sediment and soil). Because the relative exposure to both constituent ions is hence predicted to be different from the original composition of hexanoic acid, 2-ethyl-, zinc salt, basic, data for the ecotoxicological properties of hexanoic acid, 2-ethyl-, zinc salt, basic tested as such are considered less relevant for effects and risk assessment and a read-across approach to separate data for both the zinc cation and 2-ethyl hexanoate anion is preferred.

For most metal-containing compounds, it is the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of ecotoxicological concern. The solubility of hexanoic acid, 2-ethyl-, zinc salt, basic (see IUCLID section 4.8 or chapter 1.3 of the CSR) is above the range of effects concentrations for dissolved zinc in the aquatic environment (lowest acute and chronic reference values: 136 and 19 µg Zn/L, respectively, PNECfreshwater for Zn = 20.6 µg Zn/L) and therefore ecotoxicity data for soluble zinc salts can be directly used in a read-across approach for hexanoic acid, 2-ethyl-, zinc salt, basic. As a conservative approach also the ecotoxicological properties of the carboxylic acid are considered.

According to the REACH Guidance on information requirements and chemical safety assessment, chapter B.8 Scope of exposure assessment, an environmental exposure and risk assessment is mandatory for a substance if it is classified as hazardous to the aquatic environment or if it has another classification and an aquatic PNEC can be derived. The threshold for PNEC derivation is not reported in the guidance, and was set at the limit test concentration for acute toxicity tests with fish, daphnids and algae, i.e. 100 mg/L. Therefore if a substance is not classified as dangerous for the aquatic environment, but meets the criteria for at least one of the other hazard classes or categories and has L(E)C50 values < 100 mg/L, it was still considered for the environmental exposure assessment.

For hexanoic acid, 2-ethyl-, zinc salt, basic, both the Zn²⁺ ion and the 2-ethyl hexanoate anion are considered for the environmental exposure and risk assessment. Zinc is classified as hazardous to the aquatic environment (as Aquatic Acute 1, Aquatic Chronic 1), while 2-ethylhexanoic acid has an official Annex VI classification (Repr. 2) and has some key L(E)C50 values for effects on aquatic organisms < 100 mg/L (Table 1).

In case both moieties require a risk assessment, the dose additivity approach is used to explain the ecotoxicological effects of the metal carboxylate based on the data for the individual moieties. As stated in a toxicity assessment of chemical mixtures opinion for the European Commission (Scientific Committee on Consumer Safety (SCCS), Scientific Committee on Health and Environmental Risks (SCHER), and Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR). 2011. Preliminary opinion on Toxicity and Assessment of Chemical Mixtures; http://ec.europa.eu/health/scientific_committees/environmental_risks/docs/scher_o_155.pdf), the dose/concentration addition method should be preferred over the independent action approach if no mode of action information is available.

Ecotoxicological data for hexanoic acid, 2-ethyl-, zinc salt, basic are available for acute toxicity to the three trophic levels of aquatic organisms. The most sensitive test was a standard OECD 201 algae test with Pseudokirchneriella subcapitata (ErC50=2.72 mg/L; Cheshire EcoSolutions, 2013).

Read-across to the corresponding toxicity data for effect of zinc and 2-ethyl hexanoic acid and the dose additivity approach (based on the assumption of complete dissolution and a worst-case zinc content of 24% in hexanoic acid, 2-ethyl-, zinc salt, basic) results in predicted L(E)C50 values for hexanoic acid, 2-ethyl-, zinc salt, basic that are lower than the experimentally derived toxicity data for this substance (Eqn. 1, Table 1).

EC50Zn2EtH = 1 / {(weight % Zn / EC50 Zn) + (weight % 2EtH / EC50 2EtH)} (Eqn. 1)

It is therefore concluded that the read-across approach to the individual moieties is conservative. Zinc is the main driver for toxic effects to aquatic organisms and the ecotoxicity data for 2-ethyl hexanoic acid do not add significantly to the predicted toxicity for hexanoic acid, 2-ethyl-, zinc salt, basic.

Table 1: Acute toxicity data for effects of hexanoic acid, 2-ethyl-, zinc salt, basic and its moieties to aquatic organisms (only most sensitive species per trophic level).

Trophic level	Endpoint	Hexanoic acid, 2 -ethyl-, zinc salt, basic (CAS: 85203 -81 -2)	2 -ethyl hexanoic acid (CAS: 149 -57 -5)	Zinc ion
Algae	72h ErC50	2.72 mg/L (experimental, Pseudokirchneriella subcapitata); 0.57 mg/L (based on read across to zinc only); 0.56 mg/L (based on read across to both zinc and 2 -ethyl hexanoic acid)	49.3 mg/L (Desmodesmus subspicatus)	0.136 mg Zn/L (Pseudokirchneriella subcapitata)
Fish	96h LC50	100 mg/L (experimental Cyprinus carpio); 0.70 mg/L (based on read across to zinc only); 0.70 mg/L (based on read across to both zinc and 2 -ethyl hexanoic acid)	> 100 mg/L (Oryzias latipes)	0.169 mg Zn/L (Oncorhynchus mykiss)
Aquatic invertebrates	48h EC50	5 mg/L (experimental, Daphnia magna); 0.61 mg/L (based on read across to zinc only); 0.61 mg/L (based on read across to both zinc and 2 -ethyl hexanoic acid)	85.4 mg/L (Daphnia magna)	0.147 mg Zn/L (Ceriodaphnia dubia)

Conclusion on classification

The classification as hazardous to the aquatic environment of hexanoic acid, 2-ethyl-, zinc salt, basic is based on a weight of evidence approach, taking into account the data for hexanoic acid, 2-ethyl-, zinc salt, basic itself and the classification of its moieties (zinc and 2-ethyl hexanoic acid):

• Reliable acute aquatic toxicity data are available for the effect of hexanoic acid, 2-ethyl-, zinc salt, basic on the three required trophic levels (algae, invertebrates, fish). The lowest acute L(E)C50 value for the effect of hexanoic acid, 2-ethyl-, zinc salt, basic on aquatic organisms was observed for algae growth rate (ErC50 of 2.72 mg/L; Cheshire EcoSolutions, 2013) and is taken forward as the acute Exotoxicity Reference Value (ERVacute) for this substance. This ERVacute is > 1 mg/L and therefore does not result in an acute 1 classification for hexanoic acid, 2-ethyl-, zinc salt, basic.

• Assessment of chronic effects based on the acute data for hexanoic acid, 2-ethyl-, zinc salt, basic results in a chronic 2 classification for a substance that is not rapidly degradable. There is however substantial information that hexanoic acid, 2-ethyl-, zinc salt, basic can be considered as rapidly degradable:

o A reliable (Klimisch 1) GLP-conform degradation study according to OECD 301D guideline (closed bottle test) for 2-ethyl-zinc salt, basic shows >60% degradation of the organic moiety of the test substance after 7 days. It is therefore concluded that hexanoic acid, 2-ethyl-, zinc salt, basic is readily biodegradable.

o The organic moiety itself (2-ethylhexanoic acid) is rapidly degradable according to a standard OECD 301E test.

o The concept of “degradability” was developed for organic substances and is not applicable to inorganic substances like zinc. As a surrogate approach for assessing “degradability”, the concept of “removal from the water column” was developed to assess whether or not a given 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”. Under IUCLID section 5.6, the rapid removal of zinc from the water column is documented. Consequently, zinc is considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects.

Following this line of reasoning, it can be concluded that the acute toxicity data would not justify a chronic classification for hexanoic acid, 2-ethyl-, zinc salt, basic.

• The substance hexanoic acid, 2-ethyl-, zinc salt, basic has no official Annex VI classification and will dissociate into zinc and 2-ethyl hexanoate ions after dissolution in water and hence can be regarded as a mixture of both constituent ions. Zinc has an official Aquatic Acute 1 and Aquatic Chronic 1 classification (M factor 1; Annex VI of CLP Regulation EC No 1272/2008)), while 2-ethyl hexanoic acid is not classified as hazardous to the aquatic environment. For the reasons mentioned above, the zinc constituent is however considered as equivalent to being ‘rapidly degradable” in the context of classification for chronic aquatic effects. Considering this, in combination with the chronic ecotoxicity reference value for zinc of 19 µg/L, the classification of the zinc constituent for chronic aquatic effect should be “Aquatic Chronic 2”, rather than the previously mentioned official Aquatic Chronic 1 classification Taking into the weight of Zn in hexanoic acid, 2-ethyl-, zinc salt, basic (22-24%), the summation method results in an Aquatic Chronic 3 classification for hexanoic acid, 2-ethyl-, zinc salt, basic.

It is concluded that an Aquatic Chronic 3 classification for hazards to the aquatic environment is appropriate for hexanoic acid, 2-ethyl-, zinc salt, basic.