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Environmental fate & pathways

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

The substances in the lithium salts of monocarboxylic acids C14 -C22 category consist of a lithium cation and an organic fatty acid anion. The substances in the category meet the criteria for readily biodegradability though the biodegradation of the substances is relevant only to the organic section. Fatty acids biodegrade readily and completely according to the β-oxidation pathway including three major steps (activation in the cytosol, transport into mitochondria, β-Oxidation until the entire C-chain is cleaved into acetyl CoA units). The final breakdown products of the substances are carbon dioxide and water from the fatty acid anion and lithium from the cation. Thus, stable degradation products are not being formed in the environment. According to column 2 of REACH Annex VII, the ready biodegradability study of the lithium cation does not need to be conducted as the substance is inorganic. Readily biodegradability has also been demonstrated for fatty acid salts with other cations, such as sodium and potassium.

Proprietary data are available for lithium behenate showing ready biodegradability (Harlan 2013). Published data are available on lithium 12-hydroxystearate from regulatory reviews (MITI 1994, API 2008) showing ready biodegradability. The results from these studies also indicate that the lithium ion is not inhibitory to microorganisms, and does not prevent the ready biodegradation of the fatty acid component. Mizuki et al (2010) has been read across to the category, showing that a mixture of ~60% sodium oleate (C18) and ~40% potassium laurate (C12) is readily biodegradable. This indicates that shorter carbon chain length substances are expected to have the same properties as those of longer chain substances.

Experimental data on category members and data on other metal salts of fatty acids in the carbon number range of the category have been read across within the category. 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. Therefore, all of the substances in the lithium salts of monocarboxylic acids C14-C22 category are considered to be readily biodegradable.

To support this conclusion, ready biodegradation studies are currently being conducted on lithium myristate, in order to bracket the category, and fatty acids C16 -18 (even numbered) saturated and C16 -20 (even numbered) unsaturated lithium salts, to provide data on unsaturated structures (Charles River 2020).