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Toxicity to soil microorganisms

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Description of key information

The chemical safety assessment according to Annex I of Regulation (EC) No. 1907/2006 does not indicate the need to investigate further the toxicity to soil microorganisms.

Key value for chemical safety assessment

Additional information

No experimental data investigating the effects on soil microorganisms are available for Sorbitan tristearate (CAS No. 26658-19-5). Therefore, all available related data is combined in a Weight of Evidence (WoE) approach, which is in accordance to the REACh Regulation (EC) No 1907/2006, Annex XI, 1.2, to adapt the data requirements of Regulation (EC) No 1907/2006 Annex VII - X (ECHA, 2012).

In the absence of a clear indication of selective toxicity, an invertebrate (earthworm or collembolan) test is preferred, as outlined in Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance (ECHA, 2012). Read-across data in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5 from the structurally related category member Anhydro-D-glucitol trioleate (CAS No. 26266-58-0) did not show any mortality to earthworms (Eisenia fetida) in an acute terrestrial toxicity test according to OECD 207 (LC50 > 1000 mg/kg soil dw). A study with the additional read-across substance Sorbitan, octanoate (2:3) (CAS No. 91844-53-0 is ongoing, but no effects were observed in the range-finding test up to 1000 mg/L. Moreover, the read-across substance Sorbitan stearate did not show any chronic effects up to the limit of water solubility on the water flea Daphnia magna in a study according to OECD Guideline 211 (Ministry of the Environment, Government of Japan, 2006) and no effects were observed on activated sludge microorganisms with the read-across substances Sorbitan, isooctadecanoate (CAS No. 71902-01-7) (Clarke, 2012), Sorbitan laurate (CAS No. 1338-39-2) (Desmares-Koopmans, 2010) and Sorbitan, octanoate (2:3) (CAS No. 91844-53-0) (Ley, 2005). Available reliable read-across data for toxicity to aquatic microorganisms for the Sorbitan esters category members supports the determination of a lack of toxicity to soil microorganisms. No inhibition of respiration rate of activated sludge microorganisms was observed in any of the available studies for the Sorbitan category members. The Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance (ECHA, 2012) states that a test on soil microbial activity will only be additionally necessary for a valid PNEC derivation if inhibition of sewage sludge microbial activity has occurred, and this is clearly not the case. Since the substance is readily biodegradable, it will be degraded quickly. Thus, acute tests with earthworm in combination with chronic aquatic data and toxicity data on aquatic microorganisms indicating no effects up to the limit of water solubility are sufficient to assess that the Sorbitan esters category members have a very low toxicity to terrestrial organisms.

This is supported by further evidence from literature data. This data showed that soil microorganism communities are well capable of degrading fatty acid esters (Hita et al., 1996 and Cecutti et al., 2002) and use them as energy source (Banchio & Gramajo, 1997). Hita et al. investigated the degradation of the model molecule tristearin which is a triglyceride containing of glycerin tri-esterified with stearic acid in three different soils for 4 weeks. The amount of stearic acid increased in considerable amounts during the experiment showing the hydrolytic activity of lipases breaking the ester bonds. The investigation of ester fractions moreover showed the generation of new alkanoic acids (methyl stearate, ethyl stearate and propyl stearate) which were not determined in the controls. Nevertheless the amounts were no longer present after 4 weeks, which leads to the assumption that degradation by soil microorganisms had occurred. The same was shown by Cecutti et al. (2003). One soil sample was chosen and incubated with methyl oleate (plant oil) for 120 d. Methyl oleate and its metabolites were completely degraded after 60 d. Streptomyces coelicolor, a common gram-positive soil bacterium uses fatty acids (C4-C18) as sole carbon end energy source indicating that fatty acids are not-toxic and can be used for catabolism (Banchio and Gramajo, 1997). The available literature data shows that soil microorganisms are capable to break-up ester bonds and degrade fatty acids in significant amounts. Moreover, the data indicated the non-toxic properties of fatty acids since they can be used as energy source.

Taking all the available information into account in a Weight of Evidence approach in accordance with Annex XI, 1.2, effects on soil microorganisms are thus not expected to be of concern, and consequently, no further testing is required.  

 

References

Banchio, C. and Gramajo, H.C. (1997): Medium- and long-chain fatty acid uptake and utilization by Streptomyces coelicolor A3(2): first characterization of a Gram-positive bacterial system. Microbiology 143, 2439-2447.

Cecutti, C., Agius, D., Caussade, B., Gaset, A. (2002): Fate in the soil of an oil additive of plant origin. Pest Manag Sci 58, 1236-1242.

ECHA (2012) Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance. European Chemicals Agency, Helsinki

Hita, C., Parlanti, E., Jambu, P., Joffre, H., Ambles, A. (1996): Triglyceride degradation in soil. Org Geochem 25(1/2), 19-28.