Lithium isooctadecanoate

Endpoint summary

Additional information

Data have been read across from lithium 12 -hydroxystearate to lithium isooctadecanoate to complete some of the ecotoxicity endpoints. Lithium isooctadecanoate and lithium 12 -hydroxystearate are both lithium salts of C18 monocarboxylic acids, with lithium isooctadecanoate having a methyl branch on the carbon chain and lithium 12 -hydroxystearate having a hydroxyl group on the carbon chain. See IUCLID section 13 for read across justification.

  

Acute aquatic toxicity 

 

Lithium isooctadecanoate is not considered to be acutely toxic to aquatic organisms as the appropriate read across substance has acute LL or EL50s of >100 mg/L. There are no data available for lithium isooctadecanoate but an algal growth inhibition study is currently ongoing and a long-term toxicity to aquatic invertebrates study has been proposed. The dossier will be updated when the results of the algal growth inhibition study, and subsequently the long-term toxicity to aquatic invertebrates study, are available.

 

Data have been read across from lithium 12-hydroxystearate. The toxicity of lithium 12-hydroxystearate was tested experimentally (Harlan 2013). Due to the low aqueous solubility, the substance was tested as a Water Accommodated Fraction. Amounts of test item were added to the surface of the diluent at the appropriate loading rates. After the addition of the test item, the media was stirred by a magnetic stirrer using a stirring rate such that a vortex was formed to give a dimple at the water surface. The stirring was stopped after 23 hours and the mixtures allowed to stand for 1 hour. A wide bore glass tube, covered at one end with Nescofilm was submerged into the vessel, sealed end down, to a depth of approximately 5 cm from the bottom of the vessel. A length of Tygon tubing was inserted into the glass tube and pushed through the Nescofilm seal and the WAFs removed by mid-depth siphoning (the first approximate 75-100 mL discarded), using a glass wool plug if dispersed test item was seen in the aqueous phase, to give the WAFs. 

 

While ensuring that media were compatible with the water chemistry requirements of the test species, the tests on the three taxa were conducted using water from the same source with similar characteristics. As the water solubility of the substance is likely to be influenced by the hardness of the water, the ecotoxicity tests were all conducted in media with the same hardness, approximately 150 mg/L CaCO3. The changes from the standard test media were employed to reduce effects observed from variations in the formation of soap scum between the tests for different species. As far as possible, tests were also conducted concurrently in order to reduce the variation in the solubility and stability of the substance between the different tests. As the substance could not be analysed directly, both the lithium and the total organic carbon were measured in the exposure media.

 

The acute toxicity of lithium 12-hydroxystearate to fish and Daphnia and toxicity to algal growth showed no effects at a water accommodated fraction loading rate of 100 mg/L. Therefore, for fish the 96-hour LL50 is > 100 mg/L WAF, for Daphnia the 48-hour EL50 is >100 mg/L and for algal growth inhibition the 72-hour EL50 is >100 mg/L. The acute toxicities to fish, Daphnia and toxicity to algal growth were determined in GLP-compliant, limit tests following OECD guidelines 203, 202 and 201 respectively (Harlan 2013). These data were read across to lithium isooctadecanoate.

 

These data are supported by the available literature. The literature search identified two pieces of ecotoxicological data for lithium 12-hydroxystearate; a study on acute toxicity to fish and a study on toxicity to aquatic microorganisms. The API (2008) and HPV Characterisation (2003, 2009) data indicate that lithium 12-hydroxystearate has an LC50 of greater than 2000 mg/L for fish. The original reference (Stonybrook 1992) is proprietary, and a copy of the original fish study could not be obtained, the reliability assessment has been based on data reported in the review documents, with the API document giving a Klimisch score of 2, “test not conducted under full GLP regulations”. As only a summary of the study from a secondary source is available, this is not considered reliable enough for use as a key study.

 

Summary

The acute ecotoxicity data for lithium 12 -hydroxystearate have been read across to lithium isooctadecanoate. As there is no suggestion that the addition of a methyl group will affect the toxicity of the fatty acid moiety, read across from the substance is considered to be justified.

 

Lithium 12-hydroxysterate has a 96-hour LL50 of >100 mg/L WAF to fish, 72-hour EL50 of >100 mg/L WAF to algae growth and 48-hour EL50 of >100 mg/L WAF to Daphnia when conducted in ecotoxicity media at ~150 mg/L CaCO3 (Harlan 2013). As the substance is not acutely toxic to fish, Daphnia or algae, it can be justifiably expected that lithium isooctadecanoate will not be acutely toxic to aquatic organisms either.

 

This is supported by the data reviewed in the API (2008) and HPV Characterisation (2003, 2009) documents, reporting a 96-hour LC50 to fish of >2000 mg/L for lithium 12-hydroxystearate. The HPV used experimental data as well as a combination of calculated data, read across data from similar substances and technical discussion (HPV 2009) to conclude that alkali metal salts of fatty acids are unlikely to be acutely toxic at the limits of water solubility.

 

The previous algal toxicity testing lithium 12-hydroxystearate was conducted at an adjusted water hardness of 150 mg/L CaCO3. However, as there are concerns that water chemistry (such as hardness) influences the (bio)availability of the substances, it has been recommended that the new testing being conducted on lithium isooctadecanoate follows harmonised test guidelines and non-standard testing approaches, such as changes to water hardness, are avoided. Therefore, it is proposed that the new study is conducted following standard guidelines at the recommended water hardness levels for algae.

 

Chronic aquatic toxicity 

 

As the substance is poorly soluble, long-term aquatic toxicity should be addressed; therefore, a testing proposal is submitted for long-term toxicity testing on Daphnia.

 

In addition to the long-term toxicity data on the substance or relevant structural analogues, assessments of metal salts should consider the inorganic moiety if the substances dissociate rapidly or both the inorganic moiety and the substances themselves if the dissociation rate is unknown. As there is currently no experimental data on the rate of dissociation of the substance, data are presented here on the lithium ion for completeness.

 

In aqueous environments, the substance would dissociate into fatty acids and lithium ions. The fatty acids used for the formation of the salt is readily biodegradable and considered to be non-hazardous. Fatty acids of natural origin have a long history of safe use in foods. Data on the lithium component of the salts are available in the dossiers for soluble lithium salts such as lithium carbonate and lithium hydroxide.

 

In a long-term toxicity test with Daphnia magna, a LOEC of 2.53 mg Li/L and a NOEC of 1.70 mg Li/L were determined, which are equivalent to 106 and 71 mg/L for lithium isooctadecanoate. In a toxicity test with lithium hydroxide on algae, an EC50 of 87.57 mg/L and a NOEC of 5.71 mg/L for lithium hydroxide anhydrous (equivalent to 153.44 mg/L and 10.0 mg/L for lithium hydroxide monohydrate) were determined, which are equivalent to 1062 mg/L and 69 mg/L for lithium isooctadecanoate. In a toxicity test with lithium carbonate on algae, an EC50 of 400 mg/L, an EC10 of 90 mg/L and a NOEC of 50 mg/L for lithium carbonate were determined, which are equivalent to an EC50 of 3144 mg/L, an EC10 of 707 mg/L and a NOEC of 393 mg/L for lithium isooctadecanoate.

 

Lithium isooctadecanoate is surface active and forms stable dispersions rather than being truly soluble. As such, a definitive water solubility value could not be determined in the physico-chemical testing but the substance is expected to have very low solubility in water. As the water solubility of substance is likely to be low (e.g. <1 mg/L), the long-term toxicity of the substance, based on the NOEC of approximately 70 mg/L for lithium isooctadecanoate, recalculated from the result for lithium hydroxide, would be above the water solubility and therefore, no effects are expected at the limit of solubility.