Dilithium azelate

Long-term toxicity to aquatic invertebrates

Description of key information

Testing is proposed for the long-term toxicity to aqauatic invertebrates using dilithium sebacate. Although not required for the registered tonnage bands of dilithium adipate and dilithium azelate, the data from this study will be read across to other substances in the lithium salts of dicarboxylic acids C6 -C10 category for completeness.

Additional information

Although the substances in the lithium salts of dicarboxylic acids C6-C10 category have high water solubility, the substances are readily biodegradable and have low potential for bioaccumulation so there is low likelihood of long-term toxicity to aquatic species. No data are available for the long-term toxicity to aquatic species of the lithium salts of dicarboxylic acids C6-C10 to confirm this so testing is proposed for the long-term toxicity to aquatic invertebrates using dilithium sebacate.

 

Although not required for the registered tonnage bands of dilithium adipate and dilithium azelate, the data from this study will be read across to other substances in the lithium salts of dicarboxylic acids C6 -C10 category for completeness. 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 carboxylic acid chain. 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.  

 

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 dicarboxylic acids C6-C10 category, data are presented here on the lithium ion for completeness.

 

In aqueous environments, the substances in the lithium salts of dicarboxylic acids C6-C10 category would dissociate into acids and lithium ions. The acids used for the formation of the salts in this category are readily biodegradable. 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 withDaphnia magna, a LOEC of 2.53 mg Li/L and a NOEC of 1.70 mg Li/L were determined, which are equivalent to 28.8 and 19.4 mg/L for dilithium adipate. This result of a NOEC of 19.4 mg/L for dilithium adipate has been read across to all substances in the lithium salts of dicarboxylic acids C6 – C10 category, following a worst-case approach as dilithium adipate is the shortest chain length substance in the category and contains the highest proportion of lithium, calculated as 8.79% lithium.

 

Based on analysis of the lithium and acid components respectively, the water solubilities of dilithium adipate were 343 g/L and 406 g/L, for dilithium azelate were 192 g/L but the results based on azelate analysis were not conclusive and for dilithium sebacate were 76.6 g/L and 68.5 g/L. The calculated results for long-term aquatic toxicity based on lithium would be below the solubility limit of the substances. The NOEC of 19.4 mg/L calculated for dilithium adipate based on lithium toxicity will be compared to the experimental data on dilithium sebacate once this is available.