Azelaic acid, calcium salt (1:1)

Biodegradation in water: screening tests

Description of key information

In water, calcium azelate is expected to dissociate to calcium ions and azelaic acid. As it is inorganic, the calcium ion will not undergo biodegradation, however, the acid component may be biodegraded. Adipic acid (C6) is readily biodegradable based on publicly available data from five ready biodegradation tests and this result has been read across to the azelaic acid (C9), the organic component of calcium azelate. This conclusion is supported by Mizuki et al (2010), which provides data for longer-chain metal salts of carboxylic acids (approximately 60% sodium oleate (C18 unsaturated) and 40% potassium laurate (C12)).

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

In water, calcium azelate is expected to dissociate to calcium ions and azelaic acid. As it is inorganic, the calcium 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 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 calcium azelate will be readily biodegradable. Although no specific biodegradation studies are available for azelaic acid (C9), the substance would be expected to be readily biodegradable based on read across from 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 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 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 a soap-based fire-fighting agent containing long chain fatty acids (58.9% sodium oleate, 40.5% potassium laurate, 0.6% potassium palmitate) is readily biodegradable. 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 unsaturated) and ~40% potassium laurate (C12) is readily biodegradable, indicating that longer carbon chain length substances are expected to have the same properties as those of shorter chain substances. Although no data are available for azelaic acid, or the calcium salt, calcium azelate is expected to have similar environmental fate properties to other fatty acids and is considered readily biodegradable.

The overall conclusion is that calcium azelate is readily biodegradable.