Dilithium azelate

Biodegradation in water: screening tests

Description of key information

In water, the lithium salts of acids are highly soluble and are expected to dissociate to lithium ions and acids. As an inorganic metal, the lithium ion will not undergo biodegradation, however, the acid component may be biodegraded. The data for adipic acid have been read across to dilithium adipate and the other substances in the category with the overall conclusion that the lithium salts of dicarboxylic acids (C6 - C10) are readily biodegradable. 

 

Adipic acid is readily biodegradable based on publicly available data from five ready biodegradation tests and, on the basis of the ready biodegradation of the organic component, dilithium adipate is considered to be readily biodegradable. This conclusion is supported by data on a short-chain dicarboxylate lithium salt which shows that the presence of the lithium ion does not impact the degradation potential. Dilithium glutarate (C5) shows that the substance is readily biodegradable, reaching 50% degradation on day 3 and 94% degradation by day 28 of an OECD 301F manometric respirometry test (see dissemination portal).

 

Data are also presented for Mizuki et al (2010) and MITI (1999) for longer-chain metal salts of carboxylic acids. The results show that the soap-based fire-fighting agent (58.9% sodium oleate (C18’), 40.5% potassium laurate (C12), 0.6% potassium palmitate (C16)) and lithium 12-hydroxystearate (C18-OH) are readily biodegradable, indicating that the longer chain-length substances in the lithium salts of dicarboxylic acids C6-C10 category would also be readily biodegradable. A ready biodegradation test is currently ongoing with dilithium sebacate (C10) to provide data on longer chain length category members as well.  

 

This conclusion that both the shorter and longer chain length substances in the category are readily biodegradable is supported by 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).

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

In water, the lithium salts of acids are highly soluble and are expected to dissociate to lithium ions and acids. As an inorganic metal, the lithium ion will not undergo biodegradation, however, the 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).

 

There is publicly available biodegradation data for adipic acid (C6) which supports the conclusions of the CoCAM report (2014) that the organic components of 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 and their respective lithium salts would be expected to be readily biodegradable based on read across to adipic acid based on structural similarity and also on the conclusions of the CoCAM (2014) report. 

 

Adipic acid was found to be readily 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 CO₂evolution. 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 biodegradability of longer-chain fatty acids is supported by data read across from a non-GLP, non-guideline, batch respirometric study (Mizuki et al 2010). The results suggest that the soap-based fire-fighting agent (58.9% sodium oleate, 40.5% potassium laurate, 0.6% potassium palmitate) is readily biodegradable. As only a summary is available, there are limitations in design and/or reporting, but the data are taken from published, peer-reviewed literature and are considered reliable and relevant for use. Mizuki et al have shown that a mixture of ~60% sodium oleate (C18) and ~40% potassium laurate (C12) is readily biodegradable. This ready biodegradability of longer-chain length carboxylic acids is supported by other published data which list lauric acid (C12, CAS 143-07-7) as readily biodegradable (Geating 1981, Guillet et al. 1992). 

 

Data have also been read across from lithium 12-hydroxystearate, supporting that the presence of the lithium ion attached to the carboxylic acid does not impact the biodegradability. The ready biodegradability of lithium 12 -hydroxystearate was determined in a GLP-compliant modified MITI test, following OECD guideline 301C (Ministry of International Trade and Industry, Japan -MITI 1999). The biodegradation of lithium 12 -hydroxystearate was 78% on day 28, and the substance is considered to be readily biodegradable. The study was published as part of a regulatory database and is considered to be reliable and relevant for use for this endpoint. 

 

This conclusion is supported by data on a short-chain dicarboxylate lithium salt which shows that the presence of the lithium ion does not impact the degradation potential. Dilithium glutarate (C5) shows that the substance is readily biodegradable, reaching 50% degradation on day 3 and 94% degradation by day 28 of an OECD 301F manometric respirometry test (see dissemination portal).

 

The presence of the lithium ion is not expected to impact the degradation of the carboxylic acid and the available data indicate that both the shorter and longer chain length substances are expected to have the same properties and be readily biodegradable. The substances in the lithium salts of dicarboxylic acids C6-C10 category are expected to have similar environmental fate properties and the overall conclusion is that members of the lithium salts of dicarboxylic acids (C6 - C10) category are all readily biodegradable.