Zinc neodecanoate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

124.1 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

36.7 µg/L

Assessment factor:

1

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

313.3 µg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

709.6 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

340.4 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:

214.5 mg/kg soil dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.02 g/kg food

Assessment factor:

90

Additional information

Read-across approach

In the assessment of the ecotoxicity of zinc neodecanoate, 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, zinc neodecanoate will dissociate and only be present in its dissociated form, i.e. as zinc cation and neodecanoate 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 zinc neodecanoate, 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 neodecanoate 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 zinc neodecanoate, data for the ecotoxicological properties of zinc neodecanoate 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 neodecanoate 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 zinc neodecanoate (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 zinc neodecanoate. 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 zinc neodecanoate, only the Zn²⁺ ion is considered for the environmental exposure and risk assessment because zinc is classified as hazardous to the aquatic environment (as Aquatic Acute 1, Aquatic Chronic 1), while neodecanoic acid is not classified as hazardous to the aquatic environment and the key L(E)C50 values for the 3 trophic levels of aquatic organisms are all > 100 mg/L (Table 1).

Ecotoxicological data for zinc neodecanoate are only available for a standard OECD 201 algae test with Pseudokirchneriella subcapitata (Cheshire EcoSolutions, 2013). The algae test was selected because the zinc moiety is predicted to be the driver for toxic effects of zinc neodecanoate in the environment and algae are the most sensitive aquatic organisms to zinc. Read-across to the corresponding toxicity data for effect of zinc and neodecanoic acid on algae growth rate and the dose additivity approach (based on the assumption of complete dissolution and a worst-case zinc content of 18% in zinc neodecanoate) results in a predicted ErC50 for zinc neodecanoate that is lower than the experimentally derived ErC50 for this substance (Eqn. 1; Table 1).

EC50ZnNeo = 1 / {(weight % Zn / EC50 Zn) + (weight % Neo / EC50 Neo)} (Eqn. 1)

It is therefore concluded that the read-across approach to the individual moieties is conservative. The zinc moiety is the main driver for toxic effects of zinc neodecanoate to aquatic organisms and the ecotoxicity data for neodecanoic acid do not add significantly to the predicted toxicity for zinc neodecanoate.

The branching pattern of the neo-acids is not expected to have a substantial influence on the intrinsic ecotoxicological effects. A comparison of environmental fate and ecotoxicological properties for a wide range of neo-acids did not reveal consistent differences between neodecanoic acid and fatty acids, C9-13-neo (US EPA, April 2009; http://www.epa.gov/hpvis/rbp/Category_Neoacids%20C5-28_Web_April%202009.pdf).

Table 1. Acute toxicity data for effects of zinc neodecanoate and its moieties to aquatic organisms (only most senstitive species per trophic level).

Trophic level	Endpoint	Zinc neodecanoate (CAS 27253 -29 -8)	Neodecanoic acid (CAS 26896 -20 -8)	Zinc ion
Algae	72h EC50	1.69 mg/L (experimental, Pseudokirchneriella subcapitata); 0.76 mg/L (based on read-across to zinc only); 0.75 mg/L (based on read-across to both zinc and neodecanoic acid)	> 100 mg/L (Pseudokirchneriella subcapitata)	0.136 mg Zn/L (Pseudokirchneriella subcapitata)
Fish	96h LC50	No experimental data	> 100 mg/L (Oncorhynchus mykiss)	0.169 mg Zn/L (Oncorhynchus mykiss)
Aquatic invertebrates	48h EC50	No experimental data	> 1000 mg/L (Daphnia magna)	0.147 mg Zn/L (Ceriodaphnia dubia)

Conclusion on classification

The classification as hazardous to the aquatic environment of zinc neodecanoate is based on a weight of evidence approach, taking into account the data for zinc neodecanoate itself and the classification of its moieties (zinc and neodecanoic acid):

• Only an acute ErC50 value for the effect of zinc neodecanoate on algae growth rate is available (ErC50 of 1.69 mg/L; Cheshire EcoSolutions, 2013). Algae are considered as the most sensitive aquatic organisms for toxicity of zinc neodecanoate because i) algae are the most sensitive aquatic organisms for zinc and ii) neodecanoic acid is far less toxic to aquatic organisms compared to zinc. Therefore it is concluded that data on toxicity of zinc neodecanoate to fish and aquatic invertebrates are not critical for classification and the value of 1.69 mg/L 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 zinc neodecanoate.

• Assessment of chronic effects based on the acute data for zinc neodecanoate results in a chronic 2 classification for a substance that is not rapidly degradable. The zinc moiety is identified as the main driver for toxic effects of zinc neodecanoate to aquatic organisms and the ecotoxicity of neodecanoic acid is predicted not to add significantly to the predicted toxicity for zinc neodecanoate. 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 zinc neodecanoate.

• The substance zinc neodecanoate has no official Annex VI classification and will dissociate into zinc and neodecanoate 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 neodecanoic 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 account the weight of zinc in zinc neodecanoate (15-18%), the summation method results in an Aquatic Chronic 3 classification for zinc neodecanoate.

It is concluded that an Aquatic Chronic 3 classification for hazards to the aquatic environment is appropriate for zinc neodecanoate.