Sorbitan, (Z)-9-octadecenoate (2:3)

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 84.5% (CO2 evolution) in 28 days; read-across

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Two studies investigating the biodegradation of Sorbitan, (Z)-9-octadecenoate (2:3) (CAS No. 8007-43-0) are available. Since in one of the studies a marine test system was used and for the other study only a short summary is available, a read-across to the structurally related category member Anhydro-D-glucitol trioleate (CAS No. 26266-58-0) was conducted. This is in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5. Both substances are UVCBs with partly overlapping compositions. Anhydro-D-glucitol trioleate, which mainly consists of Sorbitan triester of unsaturated C18:1 fatty acids, is readily biodegradable. Generally, larger and branched molecules are considered as a worst case approach, since the chain length and substitutions are determining factors for biodegradation of fatty acid alcohol esters (Bozcar et al., 2001; Dias and Alexander, 1971). Sorbitan, (Z)-9-octadecenoate (2:3), which contains di- and triesters of the same fatty acid, is thus 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 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 marine study carried out with Sorbitan, (Z)-9-octadecenoate (2:3) (CAS No. 8007-43-0) was performed according to OECD 306 and GLP, with natural seawater as inoculum. A biodegradation of 43% was observed after 28 d. As stated in the “Guidance on information requirements and chemical safety assessment / Chapter R.7b: Endpoint specific guidance” (ECHA, 2012), biodegradation in seawater has generally been found to be slower than that in tests freshwater tests inoculated with activated sludge. This study thus supports the biodegradability of the test substance, showing that it is also degraded in the marine environment.

The additional studycarried out with Sorbitan, (Z)-9-octadecenoate (2:3) (CAS No. 8007-43-0) was performed according to OECD 301 C, with activated sludge as inoculum. After the 28-day test period, 66% biodegradation was reached. Although the documentation is not sufficient to evaluate the quality of the study, the result supports the ready biodegradability assessment of the test substance.

Thus, based on theabove mentioned results, and due to the structural and profile similarities of the substances, it can be concluded that Sorbitan, (Z)-9-octadecenoate (2:3) (CAS No. 8007-43-0) can be considered as readily biodegradable according to OECD criteria.