Barium bis(2-ethylhexanoate)

Ecotoxicological Summary

Additional information

Read-across approach

There are no ecotoxicological data available for barium bis(2-ethylhexanoate) and in the assessment of the ecotoxicity of barium bis(2-ethylhexanoate), 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, barium bis(2-ethylhexanoate) will dissociate and only be present in its dissociated form, i.e. as barium 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 barium bis(2-ethylhexanoate), but predictions of stability of other barium carboxylates (Ba propionate, Ba valerate and Ba isovalerate) 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 barium ions in solution (< 1% of total metal concentration complexed at 0.001 mM Ba; 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 Ba²⁺ 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 barium bis(2-ethylhexanoate), data for the ecotoxicological properties of barium bis(2-ethylhexanoate) tested as such are considered less relevant for effects and risk assessment and a read-across approach to separate data for both the barium 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 barium bis(2-ethylhexanoate) (see IUCLID section 4.8 or chapter 1.3 of the CSR) is above the range of effects concentrations for dissolved barium in the aquatic environment (PNECfreshwater for Ba = 227.8 µg Ba/L) and therefore ecotoxicity data for soluble barium salts can be directly used in a read-across approach for barium bis(2-ethylhexanoate). As a conservative approach also the ecotoxicological properties of the carboxylic acid are considered in the effects assessment.

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 barium bis(2-ethylhexanoate), both the Ba²⁺ ion and the 2-ethyl hexanoate anion are considered for the environmental exposure and risk assessment. Both moieties are not classified as hazardous to the aquatic environment, but have another official Annex VI classification (Acute Tox. 3 and 4 for barium chloride and Repr. 2 for 2-ethylhexanoic acid) and some key L(E)C50 values for effects of both constituents on aquatic organisms are < 100 mg/L (Table 1). Both moieties show comparable acute toxicity to aquatic organisms.

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.

Table 1: Acute toxicity data for the constituent ions of barium bis(2 -ethylhexanoate) to aquatic organisms (only most sensitive species per trophic level).

Trophic level	Endpoint	2 -ethyl hexanoic acid	Barium ion
Algae	72h ErC50	49.3 mg/L (Desmodesmus subspicatus)	> 34.3 mg Ba/L (Pseudokirchneriella subcapitata)
Fish	96h LC50	> 100 mg/L (Oryzias latipes)	> 97.5 mg Ba/L (Danio rerio)
Aquatic invertebrates	48h EC50	85.4 mg/L (Daphnia magna)	14.5 mg Ba/L (Daphnia magna)

Conclusion on classification

The substance barium bis(2 -ethylhexanoate) will dissociate into barium and 2-ethylhexanoate ions after dissolution in water and hence can be regarded as a mixture of both constituent ions. In the absence of toxicity data for barium bis(2-ethylhexanoate) itself,

its classification for environmental hazards is based on the classification of its moieties (barium and 2-ethylhexanoic acid). Both barium and 2-ethylhexanoic acid are not classified as hazardous to the aquatic environment, and according to the summation method, it is therefore concluded that barium bis(2-ethylhexanoate) is not hazardous to the aquatic environment.