Fatty acids, C16-18 (even numbered) saturated and C16-20 (even numbered) unsaturated, lithium salts

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

in vitro: - gene mutation (bacterial reversion assay/Ames test): Negative - gene mutation (mammalian cell TK+/- assay in L5178Y mouse lymphoma cells): Negative - cytogenicity (chromosomal aberration assay in human lymphocytes): Negative

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vitro:

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 fatty acid chain and the presence of unsaturated and/or hydroxyl functional groups. As a result, it is expected that the substances will have similar, predictable properties. REACH Annex V, Entry 9, groups fatty acids and their potassium, sodium, calcium and magnesium salts, including C6 to C24, predominantly even-numbered, unbranched, saturated or unsaturated aliphatic monocarboxylic acids. Provided that they are obtained from natural sources and are not chemically modified, the substances included in REACH Annex V, Entry 9 are exempt from registration, unless they are classified as dangerous (except for flammability, skin irritation or eye irritation) or they meet the criteria for PBT/vPvB substances. The fatty acid components of the category members are therefore not expected to be hazardous. As all category members are lithium salts, any toxicity is expected to be driven by the lithium ion. Due to the close structural similarity and the narrow range of carbon chain numbers covered in this category, the genotoxicity properties are expected to be similar across the category.

Although fatty acids C18 (unsaturated) lithium salts is not in the list of substances being registered, this substance falls within the definition of the lithium salts of fatty acids C14-C22 category (see Category Justification Document) by virtue of its chemical structure and therefore read across from data on fatty acids C18 (unsaturated) lithium salts to other members of the category is considered to be justified (see below).

In order to provide evidence across the C14 to C22 category, key bacterial reversion assays (Ames test) have been conducted on lithium myristate (C14), lithium 12-hydroxystearate (C18) and lithium behenate (C22), together with fatty acids C18 (unsaturated) lithium salts. In addition, a chromosomal aberration assay and a mouse lymphoma assay have been performed on the latter lithium salt. Finally, a mouse lymphoma assay was conducted on lithium myristate. In all cases, the results were negative.

A further chromosomal aberration assay has been conducted on lithium 12 hydroxystearate. Significant cytotoxicity was observed at the highest concentrations used. In all treatments in this study, there was a slight increase in the frequency of aberrant cells, which included gaps and chromosomal breaks, which were also present in negative controls. The frequency without chromosomal gaps did not exceed 5% (the lower limit used for the positive control response). There was no clear dose-dependency and the aberrant cell increase was not always reproducible in duplicate cultures. There was also induced formation of polyploid cells as a numerical aberration. In addition, rare aberration types consisting of one exchange and some dicentric chromosomes were observed in treated cultures, both with and without S9, and were not observed in either the negative controls or in historical control values in the laboratory.

Since the minor aberrations were only slightly above the concurrent and historic negative controls, were not reproducible between duplicate cultures, nor observed in a concentration-dependent manner, it can be concluded that there is little or no biological significance attached to these findings and therefore the substance did not demonstrate clastogenicity. The low level of rare findings (exchange and dicentric chromosomes) could indicate potential clastogenicity of the substance or any impurities present. However, the chromosomal aberration assay on fatty acids C18 (unsaturated) lithium salts showed no evidence of adverse chromosomal effects, and this substance also falls within the lithium salts of fatty acids C14-C22 category as indicated above. A mouse lymphoma assay on this substance also did not show the presence of small colonies which are indicative of potential clastogenicity.

In relation to the carboxylic acid anion, the SIDS Initial Assessment report for C22 docosanoic acid (2001) indicates that a chromosomal aberration assay in Chinese Hamster Lung cells to OECD TG 473 gave negative results. This was considered in the report to be a key study (Klimisch 1). The US NTP report on castor oil (C18 fatty acid triglyceride) (1992) indicates that this substance is not a clastogen in Chinese Hamster Ovary cells (nor did it induce sister chromatid exchange in this cell line). It also mentions that micronuclei were not observed in vivo in the peripheral blood erythrocytes evaluated at the end of a 13-week preliminary oral toxicity study in mice.

Studies have also been conducted on the lithium cation using inorganic lithium salts.A chromosomal aberration assay on lithium hydroxide has been performed in human lymphocytes and reported in the ECHA Dissemination Portal file for this substance. This was given a Klimisch 1 score and the substance did not show clastogenicity under the conditions of the test. Lithium carbonate has extensive therapeutic use and the paper by Leonard et al (1995) reviews the publicly available data on the mutagenic effects of lithium. It was concluded that lithium compounds have no significant clastogenic properties.

On a weight of evidence basis, the published and publicly available data indicate that the results from the chromosomal aberration study on lithium 12 hydroxystearate are considered to be anomalous and isolated and not therefore relevant for the classification of the C14 – C22 category of lithium fatty acid salts.

On the basis of the category justification, it is appropriate therefore to read across the negative genotoxicity data on lithium fatty acid salts to all C14 – C22 category members.

From the results of the experimental studies on the lithium salts of fatty acids within the C14-C22 category and reference to fatty acids in REACH Annex V, it can be concluded that there is no evidence of genotoxicity associated with the lithium cation or the fatty acid anion, and there is a significant volume of published data to indicate that the C14-C22 fatty acids within the category are not genotoxic.

Justification for selection of genetic toxicity endpoint
Study is representative of the suite of genotoxicity studies conducted.

Justification for classification or non-classification

Not classified for genetic toxicity. Negative results in all studies conducted.