Dilithium sebacate

Biodegradation in water: screening tests

Description of key information

In water the lithium salts of fatty acids are highly soluble and are expected to dissociate to lithium ions and fatty acids. As an inorganic metal, the lithium ion will not undergo biodegradation, however, the fatty acid component may be biodegraded. Adipic acid is readily biodegradable based on publicly available data from five ready biodegradation tests. It is also inherently biodegradable. This supports the conclusions of a report that includes the lithium salts of dicarboxylic acids (C6 - C10) as part of a wider aliphatics acid category (CoCAM 2014). The data for adipic acid is read across to the other substances in the category with the overall conclusion that the lithium salts of dicarboxylic acids (C6 - C10) are readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

In water the lithium salts of fatty acids are highly soluble and are expected to dissociate to lithium ions and fatty acids. As an inorganic metal, the lithium ion will not undergo biodegradation, however, the fatty acid component may be biodegraded. The OECD has published a risk assessment under the high production volume program which considers the lithium salts of dicarboxylic acids (C6 - C10) as part of a larger aliphatic acid category (CoCAM 2014). This risk assessment covers 78 member substances consisting of C4 -C22 aliphatic acids (also called fatty acids) and their salts. The CoCAM report (2014) concludes that 'the weight of evidence indicates that the aliphatics acid category members are readily biodegradable'. They share a common degradation pathway in which they are degraded to acetyl-Co A or other key metabolites in all living systems. Differences in metabolism or biodegradation of even or odd numbered carbon chain compounds are not expected (CoCAM 2014). Furthermore, the fatty acids of the lithium salts of dicarboxylic acids (C6 - C10) are all natural or chemically indistinguishable from naturally derived substances found in food.

There is publically available biodegradation data for adipic acid (C6) that supports the conclusions of the CoCAM report (2014) that the lithium salts of dicarboxylic acids (C6 - C10) will be readily biodegradable. Although no specific biodegradation studies are available for azelaic acid (C9) or sebacic acid (C10) these substances would be expected to be readily biodegradable based on read across to the other category member adipic acid based on structural similarity and also on the conclusions of the CoCAM (2014) report.

Adipic acid was found to be ready biodegradable in five ready biodegradation studies (Gerike and Fischer, 1978; Kim et al. 2001) and inherently biodegradable in a Zahn-Wellens test (Gerike and Fischer 1978). All the biodegradation studies conducted by Gerike and Fischer (1978) are based on standard methods but pre-date current OECD guideline methods. There is therefore no reporting of the criteria based on the 10 day window. There is also only limited reporting of the specific methods for these tests. The results for adipic acid in the ready biodegradation tests (based on OECD 301B, C, D and E) and in the Zahn-Wellens test (based on OECD 302B) all showed similar results to the OECD recommended reference substance Aniline with at least 83% biodegradation within 30 days (Gerike and Fischer 1978). In a Modified Sturm test following ASTM D5209 -91 adipic acid showed > 70% biodegradation in 10 days and >80% biodegradation in 30 days based on CO2 evolution. In this study adipic acid would fulfil the criteria for ready biodegradation within the 10 day window. Overall the consistent results for biodegradation in a number of different tests confirms that adipic acid is readily biodegradable.

The overall conclusion is that members of the lithium salts of dicarboxylic acids (C6 - C10) category are all readily biodegradable.

CoCAM. 2014. SIDS initial assessment profile. CoCAM 6 September 30- October 3, 2014