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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 Glycerides, C16-18 and C18-unsatd. mono- (CAS 91744-09-1) to soil microorganisms are available. However, information gathered from several independent sources is combined in a Weight of Evidence approach, which is 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. This approach provides enough evidence to state that this substance is unlikely to exert toxicity to soil microorganisms.  

The test substance is characterized by a log Kow > 5, indicating high potential for adsorption to soil particles. Tests with soil-dwelling organisms that feed on soil particles are therefore most relevant for the evaluation of soil toxicity of Glycerides, C16-18 and C18-unsatd. Mono- (Guidance on information requirements and chemical safety assessment, Chapter R7.c (ECHA, 2012)). Soil invertebrates toxicity data from a suitable read-across substance (Glycerides, C14-18 and C16-18 unsatd. mono-, di- and tri- (CAS No. 91052-28-7) in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5) are available. In this test performed according to OECD 207, no effects on survival or biomass of Eisenia fetida were reported, leading to a NOEC (14 d) ≥ 1000 mg/kg dw (Moser (2012)).

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. The test performed on Pseudomonas putida (on a suitable read-across substance, 1,2,3-propanetriyl trioleate (CAS No. 122-32-7)) showed no effects on cell multiplication up to a nominal concentration of 0.8 mg/L (EC50 (18 h) > 0.8 mg/L). The above-mentioned Guidance also states that for substances with a good biodegradation rate in a ready biodegradability test, inhibitory effects to aquatic microorganisms are not expected. This is the case for Glycerides, C16-18 and C18-unsatd. mono- (CAS No. 91744-09-1) (79% biodegradation after 28 days, read-across data).

Additionally, literature data evaluating the effects of fatty acid esters, including one of the Glyceride category members (Glycerol tristearate, CAS No. 555-43-1) to soil microorganisms are available. 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 Cecutti et al. (2002) and Banchio and Gramajo (1997) for other fatty acid esters. In the first 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. 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 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.