Lithium docosanoate

Endpoint summary

Additional information

No data are available for the toxicity to terrestrial organisms. Category members exhibit no short-term or long-term aquatic toxicity at their limit of solubility, have low potential for bioavailability (8 L/kg based on lithium) and direct and indirect emissions to soil are unlikely. Therefore, no testing has been proposed for toxicity to terrestrial organisms and the endpoints have been waived on the basis that there is expected to be no exposure of the terrestrial environment. 

 

Equilibrium partitioning 

 

The ECHA guidance document Chapter R.10 – Dose [Concentration]-Response Regarding Environment guidance document (ECHA 2008) states that “when no toxicity data are available for soil organisms, the equilibrium partitioning method is applied to identify a potential risk to soil organisms”. Equilibrium partitioning is based on estimation of the toxicity to terrestrial organisms from the aquatic toxicity and the physico-chemical and environmental fate properties of the substances. 

 

Most of the substances in this category, those with a carbon chain length of below C22, have surface active properties. Due to the surfactant nature, these substances are not truly soluble in water but form stable dispersions instead. As these stable dispersions could not be removed, it was not possible to determine water solubility values for lithium salts of monocarboxylic acids C14 to <C22 (Harlan 2012). Lithium behenate (C22) was determined to be not surface active, however only an unbounded water solubility value could be determined; the water solubility of lithium behenate was determined to be <0.000046 g/L (Harlan 2013). 

 

Due to the surface active nature of the substances, the partition coefficient also could not be determined for lithium salts of monocarboxylic acids C14 to <C22. For lithium behenate (C22), which does not have surface active properties, the partition coefficient could not be determined because the solubility in n-octanol was insufficient (Harlan 2013). The adsorption coefficient for lithium salts of monocarboxylic acids C14 to C22 could not be determined because the HPLC screening method is not valid for organic acids and could not be calculated as a partition coefficient was unavailable. 

 

The vapour pressure of the lithium salts of monocarboxylic acids C14 to C22 could not be determined because the test is technically not feasible. Standard test methods, according to OECD guideline 104, are able to measure vapour pressure from 10 E-10 Pa to 10 E+05 Pa, but the predicted vapour pressures for the substances in the lithium salts of monocarboxylic acids C14 to C22 category are below 10 E-10 Pa (US EPA 2009). 

 

Due to their surface active properties, partition coefficients could not be determined for these substances. As the water solubility, partition coefficient, adsorption/desorption coefficient and the vapour pressure could not be determined, it is not possible to use the equilibrium partitioning method to estimate the toxicity to terrestrial organisms. 

 

Soil hazard category

 

The need for terrestrial toxicity testing of a substance is dependent on the soil hazard category to which the substances are assigned and the potential for exposure of the substance to the terrestrial environment. The substances in the lithium salts of monocarboxylic acids C14-C22 category are considered to meet the criteria for soil hazard category 1 as the substances have low potential for persistence, low potential for adsorption, and are not toxic to aquatic organisms. As the substances meet the criteria for soil hazard category 1, no testing has been conducted on terrestrial organisms.

 

The substances in the category are concluded to be readily biodegradable (further testing is currently ongoing to confirm this) and the available data from short-term toxicity studies on fish, Daphnia and algae showed no effects at up to 100 mg/L loading rate. Testing is currently ongoing for algal growth inhibition of fatty acids C16-18 (even numbered) saturated and C16-20 (even numbered) unsaturated lithium salts and testing proposals are submitted for long-term toxicity toDaphniaand fish for lithium 12 -hydroxystearate, lithium myristate, lithium docosanoate and fatty acids C16 -18 (even numbered) saturated and C16 -20 (even numbered) unsaturated lithium salts.

 

No adsorption/desorption data are available as the lithium salts of monocarboxylic acids C14-C22 decompose rapidly to carbon dioxide, water and lithium ions. Metals such as sodium, potassium, calcium and lithium are expected to behave similarly, with ions in the aqueous environment remaining in solution and lithium is considered to have a low potential for adsorption based on soil Kd values(see ECHA Dissemination Portal for lithium hydroxide). Lithium is a naturally occurring element and its adsorption/desorption is not expected to be scientifically relevant.

 

Exposure 

 

The terrestrial toxicity endpoints can be waived if it can be demonstrated that direct and indirect exposure of soil is unlikely to occur. ECHA (2012) states that “In the case of readily biodegradable substances which are not directly applied to soil, it is generally assumed that the substances will not enter the terrestrial environment and as such there is no need for testing of soil organisms”. Therefore, as the substances in this category are readily biodegradable and are not applied directly to soil, testing of terrestrial ecotoxicity endpoints is not required. 

 

Furthermore, ECHA guidance document REACH Chapter R.10 – Dose [Concentration]-Response Regarding Environment (2008) states that chemicals can reach the soil via several routes: 

 

- Application of sewage sludge in agriculture - The substances in this category are used as thickeners in greases and are not expected to enter the sewage system in significant quantities (see sections 9 and 10 of the CSR). Of the amount which occurs in sewage sludge, the fatty acid component of lithium salts are readily biodegradable and the lithium ion is not expected to partition to sludge or soil but to remain in solution. Therefore, these compounds are not expected to be present in any sewage sludge applied in agriculture. 

 

- Direct application of chemicals - The substances in this category are used as thickeners in greases and none of the identified uses involves direct application to soil (see sections 9 and 10 of the CSR). 

 

- Deposition from the atmosphere - The vapour pressure of the lithium fatty acid salts in the category are estimated to be below 10 E-10 Pa and as the substances have very low volatility, they are not expected to enter the atmosphere. Thus, aerial deposition of the substances will be negligible and is not expected to be a relevant route of exposure. 

 

As the substances are readily biodegradable, have low volatility and are not applied directly to soil, it is generally assumed that they will not enter the terrestrial environment. 

 

Bioaccessibility 

 

In most cases the reactions to form the grease thickener occur in situ during the grease manufacturing process and consequently these grease thickeners normally only exist in the base oil matrix. The matrix effect, as recognised by the OECD Lubricant Emission Scenario document (OECD 2004), needs to be taken into account, as the process of manufacturing the thickener in an inert base oil is likely to influence factors such as accessibility of the thickeners. In the grease manufacturing process, unique interactions, more appropriately defined as physical bonding effects, occur between the base oils and the thickeners. The chemistry is complex and interactions between the thickener and base oil do not strictly fall under the definitions of a reaction product nor do they act as a simple mixture of components. In realistic use scenarios, the thickeners will be contained in base oil, with the formulated greases specifically designed to minimise the leaching of the thickener. Therefore, during use, the concentrations of the substances which would be bioavailable are limited. 

 

Given this, and the very low solubility of the substances in water, the concentrations of the substances which would be available for adsorption to soil or sediment are limited. This is supported by the leaching studies undertaken (see leaching summary in dossier and CSR) on grease consisting of lithium 12-hydroxystearate (10%) in distillates (petroleum), hydrotreated heavy paraffinic (CAS 64742-54-7) and/or distillates (petroleum), solvent-dewaxed heavy paraffinic (64742-65-0). The leaching study showed lithium concentrations of <0.1 mg/L in the WAF and SPME readings equivalent to background concentrations. Lithium soap-based grease thickeners have been concluded as not bioaccessible based on an interpretation of the available data. The measured concentration of lithium in the WAF of the leaching studies (<0.1 mg Li/L) was well below the NOELR for isolated lithium 12-hydroxystearate determined in the ecotoxicity studies (>100 mg/L WAF) and the NOEC for long-term toxicity to fish and Daphnia (2.87 mg/L for fish and 1.70 mg/L for Daphnia) based on lithium. The comparison of the WAF and the ecotoxicity results and the lack of effects at the limit of solubility support that the substance would not leach out of base grease at ecotoxicologically relevant concentrations. This is further supported by the results of the Microtox study conducted on the WAF from the leaching test (15-minute EL50: >100% WAF). 

 

Exposure to the isolated substance 

 

The identified uses of the substances in the lithium salts of monocarboxylic acids C14-C22 category relate to their use as thickeners in formulated greases. For these uses, the substances are typically manufactured in situ in base oil so exposure to the isolated thickeners would not occur. Additionally, although greases are considered to have wide, dispersive uses, with professional and consumer downstream users, most grease-lubricated parts are sealed. Therefore, the potential for human or environmental exposure to the formulated grease is limited and the potential for exposure to the thickener itself would be even further reduced. 

 

The majority of greased parts are designed to keep the grease within the contact zone. A large proportion of light to medium duty grease-lubricated parts are sealed for life and the user will not interact with the grease during any time of the part’s use from purchase to disposal. Due to the nature of the grease as a semi-solid, it will remain within the part and not be released, even in the event of catastrophic failure. Some applications require a grease to be used as a total loss lubricant, such as on rail tracks, heavy duty trucks, spindles on agricultural crop pickers and marine applications. In these applications, there are voluntary/compulsory schemes in place that limit the type of product used based on its toxicity, ecotoxicity and biodegradability (e.g. Nordic Swan, Ecolabel, Blaue Engel, VGP). 

 

The isolated thickener is unlikely to come in contact with the terrestrial environment. Thus, the derivation of terrestrial toxicity data on the isolated thickeners is not considered to be relevant to the potential exposure of these substances in the environment. 

 

Conclusion for terrestrial toxicity 

 

The fatty acid components of these thickeners are readily biodegradable and the lithium ion is not expected to partition to sewage sludge or soil. The thickeners have low volatility (so aerial deposition is unlikely) and are not applied directly to soil. Thus, terrestrial exposure of lithium salts of monocarboxylic acids C14-C22 is considered to be unlikely and, as the terrestrial toxicity would not be environmentally relevant, these tests have not been conducted.