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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.

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Additional information

No experimental data investigating the effects on soil microorganisms are available for ethylene distearate (CAS 627-83-8). 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 guidance section R.7.11.5.3, page 121).

The test substance is characterized by a high log Koc indicating a potential for adsorption to the soil particles. Tests with soil-dwelling organisms that feed on soil particles are therefore most relevant for the evaluation of soil toxicity of ethylene distearate. In the absence of a clear indication of selective toxicity, an invertebrate (earthworm or collembolan) test is preferred, as outlined in ECHA guidance section R.7.11.5.3, page 122. Read-across data in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5 from the structurally related category members butylene glycol dicaprylate/dicaprate (CAS 853947-59-8) and decanoic acid, mixed diesters with octanoic acid and propylene glycol (CAS 68583-51-7) did not show any mortality to earthworms (Eisenia fetida) in acute terrestrial toxicity tests according to OECD 207 and EU Method C.8, respectively (LC50 > 1000 mg/kg soil dw). A plant study with butylene glycol dicaprylate/dicaprate according to OECD 208 with three species from different taxonomic groups resulted in an EC50 of > 100 mg/kg soil for all tested species (three plant species). Moreover, the read-across substance butylene glycol dicaprylate / dicaprate 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 211 (Hertl, 2001) and no effects were observed on the respiration rate of activated sludge microorganisms (Diefenbach, 1997). Available reliable read-across data for toxicity to aquatic microorganisms for the Glycol Esters category members supports the determination of a lack of toxicity to soil microorganisms. No inhibition of respiration rate of aquatic microorganisms was observed in any of the available studies for the Glycol category members. The Guidance Document (ECHA, 2008, page 122) 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 terrestrial organisms from different taxonomic groups in combination with chronic aquatic data and toxicity data on microorganisms indicating no effects up to the limit of water solubility are sufficient to assess that the Glycol Ester category members have a very lowtoxicity 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. 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.