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Toxicity to microorganisms

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Description of key information

NOEC (3 h) ≥ 1000 mg/L (nominal)(OECD 209, activated sludge)

Key value for chemical safety assessment

Additional information

No data investigating the toxicity to aquatic microorganisms are available for methyl palmitate (CAS No. 112-39-0).

Therefore, data from a structurally related category member, methyl laurate (CAS No. 111-82-0) are used as read-across (in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5). Both substances are fatty esters esterified with methanol, differing only in the C-chain length of the fatty acid component: C16 (CAS No. 112-39-0) and C12 (CAS No. 111-82-0) respectively. Methyl laurate (C12 FA content > 80%) exhibits the highest toxicity to aquatic organisms (Daphnia and algae) throughout the whole SCAE Me category, with EC50 and NOEC values < 1 mg/L. Therefore, methyl laurate is a worst-case read across substance in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5.

The study evaluating the toxicity of methyl laurate to aquatic microorganisms (Fiebig, 2013) was conducted according to OECD Guideline 209, under GLP conditions. Activated sludge microorganisms from a municipal sewage treatment plant were exposed to the test substance for 3 hours at a concentration of 1000 mg/L (limit test). After the exposure period, no inhibiting effects of the substance on microorganisms activity were reported, leading to a NOEC (3 h) 1000 mg/L (nominal concentration).

 

In addition, methyl palmitate is poorly soluble in water (0.004 mg/L), which limits the exposure of activated sludge microorganisms in sewage treatment plants significantly. The Guidance on information requirements and chemical safety assessment, Chapter R7.b (ECHA, 2008) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Furthermore, methyl palmitate (CAS No. 112-39-0) is readily biodegradable (75% biodegradation in 28 days). According to Chapter R7.b of the Guidance on information requirements and chemical safety assessment (ECHA, 2008), for substances with a good biodegradation rate in a ready biodegradation test, inhibitory effects to aquatic microorganisms are not expected and the concentration tested (100 mg/L based on COD) can be used as a NOEC.

The lack of toxicity observed for methyl laurate (showing the highest aquatic toxicity within the category) confirms that the members of the SCAE Me category are not expected to show toxicity to aquatic microorganisms. This statement is supported by the readily biodegradable nature of these substances.

 

Based on the ready biodegradability of the substance and the results of the respiration inhibition test conducted with a structurally related category member (in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5), no toxicity to aquatic microorganisms is expected for methyl palmitate (CAS No. 112-39-0).