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Toxicity to microorganisms

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Description of key information

Fatty acids, C16-18, methyl esters is not expected to be toxic to activated sludge microorganisms and therefore, testing is not deeemed necessary

Key value for chemical safety assessment

Additional information

No data investigating the toxicity to microorganisms are available for Fatty acids, C16-18, methyl esters (CAS No. 85586-21-6).

The test substance is poorly soluble (< 1 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, Fatty acids, C16-18, methyl esters (CAS No. 85586-21-6) is considered to be readily biodegradable, with an applied test concentration of 100 mg/L (based on COD and ThOD), which is clearly above the water solubility of the substance. Biodegradation data are available from a structurally similar analogue substance, Fatty acids, C16-18 and C18-unsatd., Me esters (CAS No. 67762-38-3). Both substances contain the same fatty acid chain lengths (C16-C18) esterified with methanol and therefore their biodegradation potential is expected to be comparable. Thus, Fatty acids, C16-18 and C18-unsatd., Me esters

can be used as read-across for Fatty acids, C16-18, methyl esters in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. Based on the biodegradation result obtained for the analogue substance (87% in 28 days), Fatty acids, C16-18, methyl esters (CAS 85586-21-6) can be considered readily biodegradable according to the OECD criteria. 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 ThOD) can be used as a NOEC. Based on the above information, there is enough evidence to conclude that Fatty acids, C16-18, methyl esters (CAS No. 85586-21-6) is not inhibitory to activated sludge microorganisms and further testing is not deemed necessary.