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Toxicity to soil microorganisms

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Description of key information

The chemical safety assessment carried out 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 evaluating the toxicity of 1,2-Benzenedicarboxylic acid, di-C16-18-alkyl esters (CAS 90193-76-3) to soil microorganisms are available.

However, there is convincing evidence that toxicity to soil microorganisms is unlikely to occur. In an experimental study according to OECD 209, no effects on the respiration rate of a microbial sewage treatment community were recorded resulting in an EC50 (3 h) > 100 mg/L (nominal) (Desmares-Koopmans, 2010). Moreover, significant biodegradation was observed (51.5% after 28 d) in the key biodegradation study indicating that the initial concentration of 15.15 mg/L was not toxic to sewage treatment plant microorganisms (Desmares-Koopmans, 2010).

The Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance (ECHA, 2012; page 125) 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.

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.

Taking all information into account in a Weight of Evidence (WoE) approach which is in accordance to the REACh Regulation (EC) No 1907/2006, Annex XI General rules for adaptation of the standard testing regime no further testing with soil microorganisms is deemed necessary. This was also confirmed by ECHA in its “Decision on a testing proposal set out in a registration pursuant to article 40(3) of Regulation (EC) No 1907/2006” (Decision number: TPE-D-0000002630-83-03/F). The previous request by ECHA to perform a test on toxicity to soil microorganisms was removed based on the information presented above.