2-ethylhexyl stearate

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 80.8% (O2 consumption) in 28 days

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

There are no ready biodegradation studies available for 2-ethylhexyl stearate (CAS No. 22047-49-0). The assessment of ready biodegradability was therefore based on studies conducted with the structurally most similar category members, for which data is available, isopropyl isostearate (CAS No. 68171-33-5) and Fatty acids, C16-18, 2-ethylhexyl esters (CAS No. 91031-48-0), as part of a read across approach, which is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. Grouping of substance and read across approach. Further justification is given within the endpoint summary 6.1 and within the category justification section 13. In this case of read-across, the best suited (highest degree of structural similarity, nearest physico-chemical properties) read-across substance was entered into IUCLID. Hexadecanoic acid 2-ethylhexyl ester contains the same alcohol as 2-ethylhexyl stearate, but a two carbons shorter fatty acid. Isopropyl isostearate contains a C18 fatty acid chain as 2-ethylhexyl stearate, but branched. The first step of fatty acid alcohol ester biodegradation is the cleavage of the ester bond by lipases or esterases, (Boczar et al., 2001). The biodegradation data of hexadecanoic acid 2-ethylhexyl ester shows that the resulting 2-ethylhexol is readily degraded. Based on data on isopropyl isostearate, the isostearate moiety is also readily degraded. Since biodegradation of branched substances is usually slower compared to linear chains, biodegradation is expected to be faster for stearate than for isostearate. Therefore, since both read-across substances are readily biodegradable, 2-ethylhexyl stearate is 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 hazard assessment for this endpoint, by showing a consistent pattern of results.

The key ready biodegradability study was carried out with isopropyl isostearate (CAS No. 68171-33-5), following a procedure similar to OECD Guideline 310 and according to GLP (King, 1994). Secondary effluent from an activated sludge plant was used as inoculum. During the 28-day test period, biodegradation reached 85.6%, based on inorganic carbon analysis, and the 10-day window criterion was met.

The key study with Fatty acids, C16-18, 2-ethylhexyl esters (CAS No. 91031-48-0) was conducted according to OECD guideline 301 F and GLP (Wierich, 1999), using sewage, predominantly domestic (adaptation not specified) as inoculum. During the 28-day test period, biodegradation reach 87%, based on O2 consumption, and the 10-day window criterion was met.

Thus, based on theabove mentioned results, and due to the structural and profile similarities of the substances, as are explained with in the overall endpoint summary 6.1 it can be concluded that 2-ethylhexyl stearate (CAS No. 22047-49-0) can be considered readily biodegradable according to OECD criteria.