Fatty acids, C16-18, lithium salts

Endpoint summary

Description of key information

In vitro and in vivo studies on ocular irritation were conducted on C14, C16 and C18 fatty acid lithium salts. No classifiable irritant responses were observed for C16 and C18 fatty acid lithium salts, but irritation was seen for C14 (lithium myristate). This result was not read across to the longer chain length substances in the category since the C16 and C18 results were negative.

Key value for chemical safety assessment

Eye irritation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Additional information

The irritant/corrosivity properties of free fatty acids are chain length dependent, where the lower carbon chain length < C9 are potentially corrosive, C10 – C12 are potentially irritant and C14 above are expected to be non-irritant (HERA 2002, referencing Briggs et al, 1976 and CIR, 1987). It was expected that similar trends in properties may apply to the lithium salts of fatty acids, so testing was undertaken in a stepwise manner.

Eye irritation studies were undertaken on lithium myristate (C14) which showed that the substance is considered to be classified as an ocular irritant. As such, lithium palmitate (C16) was tested for ocular irritation and this substance was found to give negative results. This reduction in ocular irritation with increasing chain length was supported by results on longer chain length lithium carboxylate salts, with negative test results for fatty acids C18-(unsaturated) lithium salt. Therefore, lithium myristate was concluded to be an ocular irritant but the results were not read across to the other category members. Instead, the negative result for lithium palmitate was applied to the other substances in the category. Further testing on lithium 12-hydroxystearate (C18-OH) and lithium docosanoate (C22) is currently ongoing to confirm this approach.

 

Lithium myristate (C14) was tested in an OECD 405 rabbit eye irritation study but there were concerns regarding potential impurities present in the test item leading to elevated pH (a 10% preparation giving an aqueous pH before and after the rabbit eye irritation study of 10.1 drifting to 11.1 after 20 minutes). Therefore, a new sample of lithium myristate was prepared and tested in new in vitro and in vivo eye irritation studies. The new sample had a pH of ca 9.5 for a 10% preparation and pH ca 8 from a sample moistened with water. The results of all three studies confirmed lithium myristate is considered to be classified as an ocular irritant.

Lithium palmitate (C16), and Fatty acids C18 (unsaturated) lithium salts were subjected to in vitro eye irritation studies using the isolated rabbit eye or reconstituted human corneal epithelium models, and in vivo eye irritation studies in rabbits according to OECD 405 (key studies). For both substances, no classifiable irritation was observed.

Several supporting studies where grease containing approximately 5 to 13% lithium 12-hydroxystearate was tested in rabbit eyes are reported and the test materials were found to be ‘not irritating’. One reliable study (Klimisch 1) is referenced in the API Robust Summary document (2008) where lithium complex grease (containing 13.1% lithium 12-hydroxystearate and 2.6% dilithium azelate) was applied to the right eye of six rabbits. This was reported as non-irritant in the API hazard summary. The Cosmetic Ingredient Review Panel (CIR 1982) concludes that certain metal stearates (Mg, Na, Zn) were non-irritant to rabbit eye. No quality review of the data was reported and the data were either unpublished proprietary studies or from literature publications before 1960.

References

API (American Petroleum Institute) (2008) Robust Summary of Information on Grease Thickeners (Creation date: October 11, 2003. Printing date: February 20, 2009. Last update: October 20, 2008. Document date: January 11, 2005)

Briggs GB, Doyle RL, Young JA (1976) Safety studies on a series of fatty acids. American Industrial Hygiene Association Journal, vol. 37, pp. 251-252

CIR (Cosmetics Ingredients Review) (1982). Final report of the safety assessment of lithium stearate, aluminum distearate, aluminum stearate, aluminum tristearate, ammonium stearate, calcium stearate, magnesium stearate, potassium stearate, sodium stearate and zinc stearate. Journal of the American college of toxicologists, vol. 1, issue 12, pp. 143-177.

CIR (Cosmetics Ingredients Review) (1987) Final report on the safety assessment of oleic acid, lauric acid, palmitic acid, myristic acid and stearic acid. Journal of American Toxicologists, vol. 6, issue 3, pp. 321-401

HERA (Human Health and Environmental Risk Assessment on ingredients of European household cleaning products) (2002) Fatty Acid Salts (Soap) Environmental and Human Health Risk Assessment

Justification for classification or non-classification

Eye irritation: C16 -C22 fatty acid lithium salts not classified (studies were negative). C14 fatty acid lithium salts classified as eye irritant category 2.