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Toxicity to microorganisms

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Description of key information

NOEC (3 h) of ≥ 100 mg/L for activated sludge microorganisms (OECD 209)

Key value for chemical safety assessment

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Since no studies investigating the toxicity of Fatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol, sorbitan and sorbitol (CAS 93334-10-2) to microorganisms are available, in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5 a read across was conducted to the structurally related analogue substances sorbitane isooctadecanoate (CAS 71902-01-7) and sorbitan monolaurate (CAS 1338-39-2).
This read-across is justified as all substances share a comparable structure. Based on the specification the target substance Fatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol, sorbitan and sorbitol is characterized by the alcohol components sorbitol, sorbitan and 1,4:3,6-dianhydro-d-glucitol esterified as mono (mainly), -di- or tri-ester with mainly fatty acids of C18 and C18 unsaturated. The source substance sorbitan laurate (CAS 1338-39-2) is characterized as a mono-, di- and tri-ester of sorbitol with mainly C12 fatty acids. Sorbitane isooctadecanoate (CAS 71902-01-7) is an ester (mono, di and tri) of sorbitan and 1,4:3,6-dianhydro-d-glucitol with C18 branched fatty acid. Further justification is given within the endpoint summary 6.1 and within the analogue justification in section 13.

The toxicity of the source substance sorbitan isooctadecanoate (CAS 71902-01-7) to microorganisms was tested in a toxicity control during a ready biodegradation study (OECD 301B). If a compound degrades well in a ready biodegradability test, or does not inhibit the degradation of a positive control at a certain concentration, this concentration can be used as a NOEC value. This approach is in accordance with the Guidance on information requirements and chemical safety assessment (Chapter R.7b: Endpoint specific guidance, ECHA 2012b). 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 (CO2/ThCO2) occurred within 14 days (OECD guideline 301). For sorbitan isooctadecanoate a biodegradation test according to OECD guideline 301 B is available (Clarke, 2012). The test includes a toxicity control, which contains 14.4 mg/L of sorbitan isooctadecanoate and 17.1 mg/L of the reference material sodium benzoate. The toxicity control attained 82% degradation after 14 days of incubation. Hence, the substance is not toxic to aquatic microorganisms in the toxicity control and the test item concentration of 14.4 mg/L can be used as a NOEC.

The toxicity of the second source substance sorbitan laurate (CAS 1338-39-2) to microorganisms was investigated as a limit test according to the OECD Guideline 209 and GLP (Desmares-Koopmans, 2010). Activated sludge of a predominantly domestic sewage was exposed to the test concentration of 100 mg/L during 3 hours. No effect on the respiration rate of the activated sludge was observed resulting in a NOEC (3 h) ≥ 100 mg/L.

Based on the result from two structurally related read across substances (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5) it can be concluded that Fatty acids, rape-oil, mixed esters with 1,4:3,6-dianhydro-d-glucitol, sorbitan and sorbitol will not exhibit effects to microorganisms and will not inhibit the degradation process in sewage treatment plants.