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Biodegradation in water: screening tests

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Description of key information

All of the substances in the calcium salts of monocarboxylic acids C14-C22 category are considered to be readily biodegradable in water.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

All of the substances in the calcium salts of monocarboxylic acids C14-C22 category are considered to be readily biodegradable.

Fatty acids are an essential part of animal diets and are readily biodegradable. As calcium is an essential nutrient to many life forms and is found naturally in aqueous environment, it is not expected to be toxic to aquatic micro-organisms. Published and proprietary data, as well as summaries in review documents, are available for substances inside the category and structural analogues indicating that metal salts of fatty acids are readily biodegradable in the aquatic environment.

Experimental data on category members and data on other metal salts of fatty acids in the same carbon number range have been read across to substances in the calcium salts of monocarboxylic acids C14-C22 category. Read across from structural analogues are considered to be appropriate as the fatty acid anions are readily biodegradable and the metal cations are all expected to behave in a similar manner in the environment, with sodium, potassium and lithium as structural analogues, all found naturally in aqueous environments. Calcium and the structural analogues remain in solution and are expected not to be toxic to aquatic micro-organisms.

Behenate

The biodegradation of the calcium salts of monocarboxylic acids C14-C22 have been read across from lithium behenate. The ready biodegradability of lithium behenate was determined in a GLP-compliant CO2evolution study following OECD guideline 301B (Harlan 2013). Non-adapted, activated sludge from the aeration stage of sewage treatment plant which treats predominantly domestic sewage were exposed to lithium behenate at 13 mg/L for 28 days and the carbon dioxide evolution was assessed. The study was run alongside a reference substance, a blank control and a toxicity control, which indicated that lithium behenate is not inhibitory to aquatic micro-organisms at 13 mg/L. Lithium behenate reached 97% degradation after 28 days, meeting the 10 day window, and therefore is considered to be readily biodegradable.

As lithium behenate (C22), a lithium salt of the longest carbon chain length in the category, is readily biodegradable and not inhibitory to micro-organisms, this result has been read across to the calcium salts of monocarboxylic acids C14-C22 category. Lithium behenate has the same fatty acid as the longest carbon chain length substances in the category, varying only by the metal cation.

This is supported by data from HERA (Human and Environmental Risk Assessment 2003), a review document, which reported that calcium behenate showed 90% biodegradation in 10 days and is therefore considered to be readily biodegradable under anaerobic conditions. No information on the test methods used is available in the publication, though as this information is taken from a peer reviewed article, it is considered reliable and relevant for use for this endpoint. The HERA risk assessment (2003) is based on data from a range of sources, including scientific literature, IUCLID, published databases and company in-house data, which are evaluated with regard to reliability, adequacy, relevance and completeness. HERA critically evaluate data to determine if the effects observed reflect the substance’s inherent properties rather than resulting from the specific test conditions, especially with respect to sparingly soluble substances. Building on Klimisch et al. (1997), HERA has developed a series of quality criteria such that where no data meet the quality criteria but it is evident that available data are likely to be conservative, these values may be used.

Substances with shorter carbon chain lengths are expected to be more water soluble and therefore more bioavailable to aquatic microorganisms for degradation. Reading across from longer chain length substances to shorter chain length substances is therefore considered valid. As data showing the ready biodegradability of lithium behenate have been read across, all of the substances in the calcium salts of monocarboxylic acids C14-C22 category are considered to be readily biodegradable.

Stearate

Calcium stearate is considered to be readily biodegradable, as determined in a study on the biodegradation of poorly-soluble substances (ECETOC 1986) following adapted OECD 301B and OECD 301C methods. Although there are limitations in reporting, the data are taken from a published study by an industry association. Calcium stearate reached 95% biodegradation in 28 days, as determined in an unpublished proprietary study (TUV Bayern 1992) following OECD guideline 301D. Only a summary of the study is available and there is limited information on the test methods and conditions used. This is supported by the study summary in HERA (2003), which states that calcium stearate showed 85% biodegradation in 10 days and is therefore considered to be readily biodegradable under anaerobic conditions.

12-hydroxystearate

Calcium 12-hydroxystearate is considered to be readily biodegradable based on results taken from a proprietary summary of a 28 day CO2evolution biodegradation test following OECD 301B (Laboratoire d'Analyses de Fluides 2007). Aerobic sewage from a household water treatment plant was exposed to calcium 12-hydroxystearate at a concentration of 20 mg carbon/L for 28 days and the carbon dioxide evolved was measured. A toxicity control was run in parallel using sodium benzoate. Calcium 12-hydroxystearate reached 74 % biodegradation in 28 days and met the 10 day window.

Based on a study summary taken from a regulatory review document (API 2008), citing a proprietary ready biodegradability CO2 evolution test (Stonybrook 1994) following US EPA 560/6 -82 -003, calcium 12-hydroxystearate was degraded 61.5-67.6% in 28 days but did not meet the 10 day window. There is limited information available on the study but the results have been taken from a regulatory review document. As a study is available demonstrating ready biodegradation for this substance, calcium 12 -hydroxystearate is considered to be readily biodegradable.

There is very limited information available on the study but the results have been taken from a regulatory review document. The review document prepared by the American Petroleum Institute (2008) was submitted to the US EPA as part of the High Production Volume program. The EPA website states that the EPA’s OPPT uses methods established in EPA guidance, which are similar to those described in Klimisch et al. (1997), to evaluate data submitted under the HPV Challenge Program for its quality and completeness. A two tier assessment is used to assess overall scientific integrity of the information, with initial screening followed by a more rigorous evaluation. Therefore, although the method used is not known, the values presented here are acceptable as they are from a reliable secondary source.

Tallowate

Data from HERA (2003), a review document, reported that fatty acids, tallow, calcium salt is considered to be biodegradable. No information on the test methods used is available in the publication, though as this information is taken from a peer reviewed article, it is considered reliable and relevant for use for this endpoint.

Laurate

Although no data are available for the biodegradation potential of calcium myristate, results have been read across from Mizuki (2010), which has shown that a mixture of ~60% sodium oleate (C18) and ~40% potassium laurate (C12) is readily biodegradable as determined in a non-GLP, non-guideline, batch respirometric study. This indicates that shorter carbon chain length fatty acid salts are expected to have the same properties as those of longer chain fatty acid salts. As a mixture containing metal salts of C12 and C18 fatty acids are readily biodegradable, it is expected that salts of myristic acid (C14), which falls between these two chain lengths would also have the same properties.

Summary

All of the substances in the calcium salts of monocarboxylic acids C14-C22 category are considered to be readily biodegradable.

This ready biodegradability is shown by the available data, which indicate that metal salts of fatty acids with carbon chain lengths of C16, C18 and C18 (hydroxylated), C22 and a mixture of salts of fatty acids with chain lengths predominantly C12 and C18 are readily biodegradable.

References

Klimisch HJ, Andreae M, Tillmann U (1997) A systematic approach for evaluating the quality of experimental toxicological and ecotoxicological data. Regulatory toxicology and pharmacology, vol. 25, pp. 1-5

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