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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 the members of the PFAE aromatic category. 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 Annex VII - X.

The terrestrial toxicity of the PFAE aromatic category members has been tested on the earth worm Eisenia fetida with the category member 1,2,4-Benzenetricarboxylic acid, mixed decyl and octyl triesters (CAS No. 90218-76-1). No mortality was observed during the 14-day exposure period at the test concentration of 1,000 mg/kg soil dw. Additionally, data is also available from a test with terrestrial plants for the same substance. The 17-day EC50 value was > 100 mg/kg for all plants tested.

According to Chapter R7.b of the Guidance on information requirements and chemical safety assessment (ECHA, 2012), 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. Since the members of the PFAE aromatic category are considered to be enhanced ultimately biodegradable by activated sludge microorganisms and show no inhibitory effects on the growth of Pseudomonas putida up to a concentration of 1000 mg/L, toxic effects on terrestrial microorganisms are unlikely.

Additionally, this assumption 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.

 

Based on the information above, terrestrial toxicity is not of concern for PFAE aromatic category members.