Fatty acids, C16-18 and C18-unsatd., Bu esters

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 76 - 81% (CO2 evolution) in 28 days

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Since no ready biodegradability studies are available for Fatty acids, C16-18 and C18 unsaturated, butyl esters (CAS No. 84988-74-9), the assessment was based on studies conducted with the structurally most similar category members, for which data is available, Fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters (CAS No. 85049-37-2) and Fatty acids, C16-18 and C18 unsaturated, isobutyl esters (CAS No. 84988-79-4) as part of a read-across approach. This 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. Both read-across substances have the same composition of fatty acids as Fatty acids, C16-18 and C18 unsaturated, butyl esters. Due to their larger and/or branched alcohol moieties, isobutyl and 2-ethylhexyl, they are expected to be less well biodegraded than Fatty acids, C16-18 and C18 unsaturated, butyl esters. Consequently, since both read-across substances are readily biodegradable, Fatty acids, C16-18 and C18 unsaturated 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 study with Fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters (CAS No. 85049-37-2) was performed according to OECD guideline 301 B (Van der Kerken, K., 1995), using domestic activated sludge as inoculum. During the 28-day test period, biodegradation reached 76 - 81%, based on CO2 evolution, and the 10-day window criterion was met.

The key ready biodegradability study, conducted with Fatty acids, C16-18 and C18 unsaturated, isobutyl esters (CAS No. 84988-79-4), was performed according to OECD guideline 301 D (Richterich, 2001). Effluent from a domestic sewage treatment plant was used as inoculum. During the 30-day test period, biodegradation reached 99%, based on O2 consumption, and the 10-day window criterion was met. After 28 days, degradation was ca. 95%, as can be seen in the degradation curve, although this value is not reported. Additional analytical determinations indicated a nitrification of the nitrogen containing (1.4 mg/L NH4Cl) mineral test medium. Taking into account a total nitrogen oxidation (worst case max. oxygen demand 2.03 mg O2/L) to nitrate, at least 65% of the test substance was degraded within 32 days of test period.Since the substance is a UVCB and thus consists of saturated and unsaturated 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 this UVCB substance and due to a degradation of > 60% within 28 days the substance can be regarded as readily biodegradable.

Thus, based on theabove mentioned results, and due to the structural and profile similarities of the substances, as are explained within the overall endpoint summary 6.1 it can be concluded that Fatty acids, C16-18 and C18 unsaturated, butyl esters (CAS No. 84988-74-9) can be considered readily biodegradable according to OECD criteria.