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Long-term toxicity to aquatic invertebrates

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Description of key information

Testing is proposed for the long-term toxicity to Daphnia using lithium 12-hydroxystearate, lithium myristate, lithium docosanoate, and fatty acids C16 -18 (even numbered) saturated and C16 -20 (even numbered) unsaturated lithium salts. The data from these studies will be read across to other substances in the lithium salts of monocarboxylic acids C14 -C22 category.

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Additional information

No data are available for the long-term toxicity to aquatic species of the lithium salts of monocarboxylic acids C14-C22. Testing is proposed for the long-term toxicity to Daphnia using lithium 12-hydroxystearate, lithium myristate, lithium docosanoate, and fatty acids C16 -18 (even numbered) saturated and C16 -20 (even numbered) unsaturated lithium salts. The data from these studies will be read across to other substances in the lithium salts of monocarboxylic acids C14 -C22 category. The substances in the category are considered to be similar on the basis that they have common structures of a lithium ion varying only by the length of the fatty acid chain and the presence of unsaturated and/or hydroxyl functional groups. As a result, it is predicted that the substances will have similar, predictable properties. Due to the close structural similarity and the narrow range of carbon chain numbers covered by the category, the aquatic ecotoxicity is expected to be similar across the category. 

  

No data are available for the long-term toxicity to aquatic species of the lithium salts of monocarboxylic acids C14-C22. The substances in the lithium salts of monocarboxylic acids C14-C22 category are readily biodegradable and have low potential for bioaccumulation. It was not possible to measure the water solubility of the substances as they are not truly soluble in water but form stable dispersions instead. In environmental media, the substances form a scum dispersed within the water and it is therefore expected that the substances have limited bioaccessibility. In realistic use scenarios, the thickeners will be contained in base oil, with the formulated greases specifically designed to minimise the leaching of the thickener. Therefore, during use, the concentrations of the substances which would be bioaccessible are further limited. The leaching investigations undertaken on these substances support that the substances would not be bioaccessible - for further information see section 5.6 of IUCLID. 

 

In addition to the long-term toxicity data on category members, assessments of metal salts should consider the inorganic moiety if the substances dissociate rapidly or both the inorganic moiety and the substances themselves if the dissociation rate is unknown. As there is currently no experimental data on the rate of dissociation of the substances in the lithium salts of monocarboxylic acids C14-C22 category, data are presented here on the lithium ion for completeness.

 

In aqueous environments, the substances in the lithium salts of monocarboxylic acids C14-C22 category would dissociate into fatty acids and lithium ions. The fatty acids used for the formation of the salts in this category are readily biodegradable and are considered to be non-hazardous. Fatty acids of natural origin have a long history of safe use in foods and, under the REACH regulation Annex V, natural C6 to C24 fatty acids are exempt from registration. Data on the lithium component of the salts are available in the dossiers for soluble lithium salts such as lithium carbonate and lithium hydroxide. In a long-term toxicity test with Daphnia magna, a LOEC of 2.53 mg Li/L and a NOEC of 1.70 mg Li/L were determined, which are equivalent to 85.4 and 57.4 mg/L for lithium myristate. This result of a NOEC of 57.4 mg/L for lithium myristate has been read across to all substances in the lithium salts of monocarboxylic acids C14 - C22 category, following a worst-case approach as lithium myristate is the shortest chain length substance in the category and contains the highest proportion of lithium, calculated as 2.96% lithium.

 

Most of the substances in the category are surface active and form stable dispersions rather than being truly soluble. As such, definitive water solubility values could not be determined in the physico-chemical testing but the substances are expected to have very low solubility in water. A water solubility value of ≤0.000046 g/L (equivalent to ≤0.046 mg/L) was determined for lithium behenate (C22), and the other category members with shorter chain lengths would be expected to have similarly low water solubilities. As the water solubility of substances in the category is likely to be low (e.g. <1 mg/L), the long-term toxicity of the substances to invertebrates, based on the NOEC of 57.4 mg/L for lithium myristate, recalculated from the result for lithium hydroxide and read across to all substances in the lithium salts of monocarboxylic acids C14 - C22 category, would be above the water solubility and therefore, no effects are expected at the limit of solubility.