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Toxicity to microorganisms

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Description of key information

EC50 (6 h) > 10 mg/L (cell multiplication inhibition test with Pseudomonas putida according to Bringman and Kuehn (1980))

Key value for chemical safety assessment

Additional information

In accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 a read across to three structurally related category members pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids (CAS-No. 68424-31-7), decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS 71010-76-9) and 2-ethyl-2-[[(1-oxoheptyl)oxy]methyl]propane-1,3-diyl bisheptanoate (CAS 78-16-0). This read-across is justified in detail in the overall summary (IUCLID chapter 6.1) and within the category justification in IUCLID Section 13. In this case of read-across, the best suited (highest degree of structural similarity, nearest physico-chemical properties) read-across substances were used for the assessment. The fatty acid chain length of C5 – C10 of the first two read-across substances are similar to those of the target substance and both substances contain the same alcohol (pentaerythritol) and are tetra-esters. The third read-across substance is a TMP tri-ester with a fatty acid chain length of C7.

The first study investigating the toxicity of read-across substance pentaerythritol tetraesters of n-decanoic, n-heptanoic, n-octanoic and n-valeric acids (CAS-No. 68424-31-7) to microorganisms was conducted as a cell multiplication inhibition test with Pseudomonas putida according to Bringman and Kuehn (1980) (Comber and Coleman, 1991). No inhibition on the growth was observed at the tested concentration (EC10 and EC50 (6 h) > 10 mg/L (nominal)). The second read across study investigating toxicity to aquatic microorganisms was conducted with decanoic acid, mixed esters with heptanoic acid, octanoic acid, pentaerythritol and valeric acid (CAS No. 71010-76-9) under static conditions according to OECD 209 (Dickinson, 2008). In this study non-adapted activated sludge obtained from a domestic sewage treatment plant was used as inoculum. Test concentrations of 10, 100 and 1000 mg/L were prepared. Test substance was added directly to the test vessels. The test substance did not inhibit the respiration rate of activated sludge microorganisms at any of the concentrations employed in the test. Hence, the 3 h-EC50 was determined to be > 1000 mg/L based on the nominal test concentration. Therefore, it can be concluded that the test substance will not exhibit effects on the respiration rate of microorganisms.

Regarding the third read-across substance, 2-ethyl-2-[[(1-oxoheptyl)oxy]methyl]propane-1,3-diyl bisheptanoate (CAS 78-16-0), the assessment of the toxicity to microorganisms is based on the NOEC determined in the toxicity control reported in the study on ready biodegradability. This approach is suitable for substances with high degrading rates or no degradation inhibition in the positive control in ready biodegradability tests. This is in accordance with the Guidance on information requirements and chemical safety assessment (Chapter R.7b: Endpoint specific guidance, ECHA 2012). A substance can be assumed to be not inhibitory to aquatic microorganisms, if in the toxicity control of a ready biodegradation test more than 25% degradation based on CO2 evolution occurred within 14 days (OECD guideline 301). For 2-ethyl-2-[[(1-oxoheptyl)oxy]methyl]propane-1,3-diyl bisheptanoate (CAS 78-16-0) a biodegradation test according to OECD guideline 301B is available (Muckle, 2009). The test includes a toxicity control, which contains 30.4 mg/L of the test substance and 26.8 mg/L of the reference material (Anilin). The toxicity control attained 41.8% degradation after 4 days of incubation (80.4% after 14 d). Hence, the substance is not toxic to aquatic microorganisms and the test item concentration of 30.4 mg/L in the toxicity control can be used as NOEC.

Based on these results from structurally related read-across substances which are characterized by a similar ecotoxicological profile, it can be concluded that 2,2-bis[[(1-oxopentyl)oxy]methyl]propane-1,3-diyl divalerate (CAS-No.15834-04-5) will not have adverse effects on the respiration rate of microorganisms, therefore, a disturbance in the biodegradation process of a sewage treatment plant is not anticipated. As it can be seen in the data matrix of the category justification in section 13 and the overall endpoint summary IUCLID 6.1, all reliable data in the polyol esters category support this hazard assessment by showing a consistent pattern of results, i.e. no microbial inhibition and no toxic effects were observed to aquatic organisms up to the limit of water solubility.