Lithium stearate

Bioaccumulation: aquatic / sediment

Description of key information

Lithium is expected to have a low potential for bioaccumulation, with a BCF of around 8 L/kg in freshwater fish. Taken together with the lithium salts of fatty acids being readily biodegradable and the fatty acid components themselves being either natural or chemically indistinguishable from natural substances with a long history of safe use in foods, the substances in the lithium salts of monocarboxylic acids C14-C22 category are not considered to bioaccumulate in the aquatic environment.

Additional information

No data are available for the bioconcentration in aquatic species of the lithium salts of monocarboxylic acids C14-C22.

 

The bioaccumulation endpoint can be waived if the substance has a low potential for bioaccumulation, as indicated by a log Kow of less than 3. Due to the surface active nature of the substances and the low solubility in octanol, the octanol-water partition coefficient could not be measured but lithium myristate and lithium 12-hydroxystearate have QSAR predicted log Kow values of <3 (2.2 and 2.6, respectively) (US EPA 2011). 

 

It was not possible to measure the water solubility of the substances as they are not truly soluble in water but form stable dispersions instead. In environmental media, the substances form a scum dispersed within the water and it is therefore expected that the substances have limited bioavailability. 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 bioaccessible (and thus bioavailable) are further limited. To support this, investigations were undertaken by the ERGTC (Shell 2013), in which Water Accommodated Fractions (WAFs) of grease (thickeners in base oil) samples were prepared at loading rates of 1000 mg/L. After 72 hours, chemical analysis of the WAFs showed a lithium concentration of <0.1 mg/L in the WAF and SPME readings equivalent to background concentrations. On the basis of the available experimental data for lithium 12-hydroxystearate, lithium salts of monocarboxylic acids C14-C22 are concluded to be not bioaccessible and therefore the substances have low potential to cross biological membranes. 

 

Although the endpoint has been waived, data on the fatty acid and lithium components of the category members are also provided for reference. The fatty acids used for the formation of the salts in this category are either natural substances or chemically indistinguishable from natural substances. The fatty acid components of the substances are considered to be non-hazardous. Fatty acids of natural origin have a long history of safe use in foods and, under the REACH regulation Annex V, natural C6 to C24 fatty acids are exempt from registration. In addition, fatty acids in the range C14-22 are considered to be readily biodegradable based on the data presented in this dossier, and therefore, bioaccumulation data are presented here for the lithium component only. 

 

Barber et al. (2006) provide a BCF for lithium in Gambusi (whole body) of 5 L/kg and in Tilapia of 2 L/kg (fillet) and 8 L/kg (liver). The bioconcentration factor of lithium in two species of fish, Gambusi and Tilapia, was determined in a non-GLP, non-guideline study published in a peer-reviewed journal. The study measured the lithium concentration in constructed secondary effluent wastewater wetlands and the lithium concentration in whole Gambusia and the fillets and livers of Tilapia fish living in the wetlands and used the data to calculate a bioconcentration factor for lithium in freshwater fish. There are limitations in design and/or reporting, but the study follows sound scientific principles and is considered reliable and relevant for use for this endpoint. 

 

Karlsson et al. (2002) provide a bioaccumulation factor for lithium of 1 in the edible parts of marine and freshwater fish, citing data from the National Council on Radiation Protection and Measurements, USA (NCRP, 1996). No further information on the source of the data, the review or evaluation of the data or the choice of value is provided. However, they note that a 10-fold error is likely according to a review of other available data. Even so, the BAF reported are very low. 

 

Although, Pokorska et al. (2012) do not directly provide any information on bioconcentration factors, they do indicate that the mean lithium concentrations in muscles, kidney and liver of flounder obtained from the South Baltic sea are 0.017 ± 0.007 mg/kg wwt, 0.044 ± <0.001 mg/kg wwt and 0.010 ± 0.009 mg/kg wwt, respectively. The concentrations in Baltic herring were determined to be 0.010 ± 0.010 mg/kg wwt for muscles and 0.015 ± <0.001 mg/kg wwt for liver, though the concentration in the kidneys was not determined. The concentration of lithium in flounder and herring was determined in a non-GLP-compliant, non-guideline study, published in a peer-reviewed journal. Flounder and herring (twenty of each species) were collected from the southern Baltic Sea, the muscles, liver and kidneys digested separately and the lithium content determined by ICP-AES. There are limitations in design and/or reporting, but the study is otherwise considered adequate for assessment. Using a lithium concentration in seawater of 170 to 190 µg/L (Aral and Vecchio-Sadus 2008), the bioconcentration factors were all calculated to be below 1. 

 

The bioaccumulation of lithium in largemouth yellowfish and their parasitic worms was determined in a non-GLP-compliant, non-guideline study, published in a peer-reviewed journal (Retief 2009). Twenty largemouth yellowfish (Labeobarbus kimberleyensis), along with water and sediment samples, were collected from Vaal Dam, South Africa. The muscle, spinal cord, liver and intestinal parasites were digested separately and the lithium concentration in each of the samples was determined by ICP-MS. No significant difference was observed when the lithium concentrations in water and sediment were compared to the liver, muscle, spinal cord of largemouth yellowfish (Labeobarbus kimberleyensis) and tapeworms (Bothriocephalus acheilognathi), indicating that lithium is not bioaccumulated. There are limitations in design and/or reporting, but the study is otherwise considered adequate for assessment. 

 

In a study by Retief et al. (2006), lithium was not accumulated in the liver, muscle or spine of fish (Labeobarbus kimberleyensis) collected from a South African reservoir, indicating that BCF value would be very low. However, it was observed to accumulate in parasitic worms found in the guts of these fish. No BCF values were calculated, and the lithium concentration in the water was not reported. The parasites would have been exposed to lithium in the gut of the fish, rather than the water to which the fish were exposed, further complicating any calculation of BCF values. The lithium concentration in the parasites was approximately 0.036 μg/g (wwt). A typical range of lithium concentrations in freshwaters has been reported by Aral and Vecchio-Sadus (2008) as 0.07 to 40 μg/L. Using these values, a range of BCF values can be estimated (based on the exposure of the fish within which the parasites were present). Following this approach, a range of BCF values can be calculated from 0.9 to 514. Using the geometric mean of the minimum and maximum lithium concentrations in surface waters (1.7 μg/L) a generic BCF value of 21.5 is calculated. 

 

Although none of these studies follow standard guidelines, the available data indicate that the lithium component of the fatty acid salts is expected to have a low bioaccumulation factor. Taken together with the lithium salts of fatty acids being readily biodegradable and the fatty acid components themselves being either natural or chemically indistinguishable from natural substances with a long history of safe use in foods, the substances in the lithium salts of monocarboxylic acids C14-C22 category are not considered to bioaccumulate in the aquatic environment and subsequently are not expected to pose a risk of secondary poisoning.