Sorbitan tristearate

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 88% (O2 consumption) in 28 days; read-across

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Since no studies investigating the ready biodegradability of Sorbitan tristearate (CAS No. 26658-19-5) are available, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5, a read across to the structurally related category members Sorbitan stearate (CAS No. 1338-41-6) and Anhydro-D-glucitol trioleate (CAS No. 26266-58-0) was conducted. Sorbitan tristearate and Sorbitan stearate are both Sorbitan esters of C18 unsaturated fatty acids. Sorbitan stearate, which mainly consists of monoester, was shown to be readily biodegradable. Since Sorbitan tristearate has higher degree of esterification, the read-across to Anhydro-D-glucitol trioleate was used to demonstrate the ready biodegradability of C18 triesters. Since both Sorbitan stearate and Anhydro-D-glucitol trioleate are readily biodegradable, Sorbitan tristearate can be expected to be readily biodegradable as well. Furthermore, as can be seen in the data matrix of the category justification in Section 13, all reliable data in the category support the biodegradability assessment of each category member, by showing a consistent pattern of results.

The key study was carried out with Sorbitan stearate (CAS No. 1338-41-6), following the OECD Guideline 301 C and according to GLP (MoE, 1996). A mixed inoculum containing microorganisms from sewage plants and from natural waters was used. During the 28-day test period, biodegradation reached 88%, based on O2 consumption. Since Sorbitan stearate is a UVCB substance and consists of structurally similar constituents with different chain-lengths, sequential (instead of concurrent) biodegradation of the individual structures can take place, but all 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 this UVCB substance and due to a degradation of >60 % within 28 days the substance can be regarded as readily biodegradable.

The key study carried out with Anhydro-D-glucitol trioleate (CAS No. 26266-58-0) was performed following the OECD Guideline 301 B (van Dievoet, 2006). The inoculum was obtained from a domestic sewage treatment plant. During the 28-day test period, biodegradation reached 88.9%, based on CO2 evolution. The 10-day window criterion was fulfilled.

Thus, based on theabove mentioned results, and due to the structural and profile similarities of the substances, it can be concluded that Sorbitan tristearate (CAS No. 26658-19-5) can be considered as readily biodegradable according to OECD criteria.