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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 evaluating the toxicity of methyl hexanoate (CAS No. 106-70-7) to soil microorganisms are available.However, information gathered from several independent sources of information (Weight of Evidence approach, in accordance to the REACh Regulation (EC) No. 1907/2006, Annex XI General rules for adaptation of the standard testing regime set out in Annexes VII to X, 1.2, to cover the data requirements of Regulation (EC) No. 1907/2006, Annex IX) provide enough evidence to state that this substance is unlikely to exert toxicity to soil microorganisms.

 

Soil invertebrates toxicity data from a suitable read-across substance (methyl laurate (CAS No. 111-82-0) in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5) are available. In this test performed according to OECD 222, no effects on survival, reproduction or growth of Eisenia fetida were reported, leading to a NOEC = 1000 mg/kg dw (Winkelmann (2013)).

 

According to Chapter R7.b of the Guidance on information requirements and chemical safety assessment (ECHA, 2008), a test on soil microbial activity will be additionally necessary for a valid PNEC derivation only if inhibition of sewage sludge microbial activity has occurred. The test performed with methyl laurate (a suitable read-across substance) on aquatic microorganisms showed no inhibitory effectson activated sludge microorganisms activity (NOEC (3 h) 1000 mg/L (nominal)(Fiebig,2013).

 

Additionally, literature data evaluating the effects of fatty acid esters, including a methyl ester compound, methyl oleate (CAS No. 112-62-9)(Cecutti et al., 2002). In this test, one soil sample was chosen and incubated with methyl oleate (plant oil) for 120 days. Methyl oleate and its metabolites were completely degraded after 60 days. Hita et al. (1996) investigated the degradation of the model molecule tristearin (Glycerol tristearate) 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. Furthermore, the investigation of ester fractions 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 Banchio and Gramajo (1997) for other fatty acid esters. 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. 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.

 

Based on all the available information for the 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.

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within CSR.