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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Readily biodegradable: 62.5% to 88% after 28 d (OECD 301 C and F); read-across

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Since no studies investigating the ready biodegradability of sorbitan C16-18 (even numbered) fatty acid esters, ethoxylated (1-6.5 moles ethoxylated) are available, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5, a read across to the structurally related substances sorbitan stearate (CAS 1338-41-6) and sorbitan monolaurate, ethoxylated (CAS 9005-64-5) was conducted.

The first available study tests the ready biodegradability of the read across substance sorbitan stearate (CAS 1338-41-6) according to the OECD guideline 301 C and GLP (MoE, 1996). A mixed inoculum containing microorganisms from sewage plants and from natural waters was used. During the 28 d test period, biodegradation reached 88%, based on O2 consumption. In conclusion, sorbitan stearate (CAS 1338-41-6) is considered readily biodegradable according to OECD criteria.

The second available study for the read across substance sorbitan monolaurate, ethoxylated (CAS 9005-64-5) was conducted according to the OECD guideline 301 F and GLP (Simon, 2012). Activated sludge from a municipal sewage treatment plant was used as inoculum. The biodegradation was tested at two substance concentrations (25 mg/L and 100 mg/L). During the 28 d test period the test assay containing 25 mg test substance/L reached a biodegradation rate of 62.5%, based on O2 consumption. The substance was degraded by 54% at the end of the 10 - day window. Thus, the 10 - day window was not met. 

Since the substance is an UVCB and thus consists of constituents with different chain lengths, sequential (instead of concurrent) biodegradation can take place, but all constituents can be considered as readily biodegradable. Thus, referring to Annex I to the OECD Guideline for Testing of Chemicals ‘Revised introduction to the OECD guidelines for testing of chemicals, section 3’ (OECD, March 2006), the 10 - day window should not be considered for UVCB substances and due to a degradation of > 60% within 28 d the substance can be regarded as readily biodegradable.

A toxicity control was set up containing 100 mg/L test item and 100 mg/L sodium benzoate. No inhibitory effects of the test item were observed (more than 25% degradation occurred within 14 d) in the toxicity control.

On the basis of the two above described key studies with appropriate read across substances, it can be assumed that the UVCB substance sorbitan C16-18 (even numbered) fatty acid esters, ethoxylated (1-6.5 moles ethoxylated) will be readily biodegradable within 28 d.