Lithium isooctadecanoate

Toxicity to microorganisms

Description of key information

The activated sludge respiration inhibition test does not need to be conducted as the substance is readily biodegradable at the range of concentrations that can be expected in the influent of a sewage treatment plant.

Additional information

Lithium isooctadecanoate is considered to be readily biodegradable based on data read across from lithium 12 -hydroxystearate and isooctadecanoic acid, and therefore no testing on the toxicity to microorganisms has been conducted. A ready biodegradation study on lithium isooctadecanoate is currently ongoing to confirm this conclusion and, when available, the results of the toxicity control will be used as supporting evidence for waiving the toxicity to micro-organisms endpoint.

The lack of toxicity to micro-organisms is supported by data on other lithium salts of monocarboxylic acids. The toxicity of lithium behenate (EC 224 -801 -1, lithium salt of C22 straight chain) to aquatic micro-organisms was taken from the inhibition control of a GLP-compliant ready biodegradability test following OECD guideline 301B (Harlan 2013). 39.6 mg of lithium behenate was dispersed in 400 mL mineral medium by high shear mixing (approximately 7500 rpm) for 15 minutes and 51.4 mL sodium benzoate stock solution were added to mineral medium inoculated with 30 mg/L suspended solids mixed population of activated sewage sludge and adjusted to 3 L, giving a final concentration of 13.2 mg/L lithium behenate and 17.1 mg/L sodium benzoate. The test vessels were sealed, the evolved carbon dioxide collected and samples from the carbon dioxide absorber vessels analysed on days 0, 2, 6, 8, 10, 14, 21, 28 and 29 for calculation of the percentage degradation. This toxicity control vessel attained 74 % degradation after 14 days and 83 % degradation over 28 days, which are above the 25 % required for substances to be considered as non-inhibitory, thereby confirming that lithium behenate was not toxic to sewage treatment micro-organisms used in the test.

Although data relate to lithium behenate (lithium salt of C22 fatty acid), lithium isooctadecanoate is expected not to be inhibitory to micro-organisms either as it is considered to be readily biodegradable with no toxicity to Daphnia or algae at up to 100 mg/L. Data on lithium salts of monocarboxylic acids C14 -C22 indicate similarities in environmental fate and ecotoxicity properties across the substances with different chain lengths, with and without unsaturated double bonds and/or hydroxyl groups, and these similarities would be expected for lithium isooctadecanoate as well, varying as it does from the substances in the category by the presence of a single methyl branch on the carbon chain.