Hexadecyl 2-ethylhexanoate

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 90% (CO2 evolution) in 29 days (OECD 301B)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Since no studies investigating the ready biodegradability of Hexadecyl 2-ethylhexanoate (CAS No. 59130-69-7) are available for this endpoint, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 a read-across to the structurally related source substance Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0) is conducted.

A read across from Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0) to Hexadecyl 2-ethylhexanoate (CAS No. 59130-69-7) to cover the biodegradation endpoint is acceptable as first, both substances have common functional groups being esters of 2-ethylhexanoic acid and fatty alcohols with carbon length of C16 - C18 and C14 - C18, respectively. Second, both substances have the common precursor 2-ethylhexanoic acid and fatty alcohol and common breakdown products as both are expected to be rapidly metabolised in the body via enzymatic hydrolysis to the starting materials (e.g., see Barron et al. 1999 for metabolism of esters in fish), which then fed into body’s natural catabolic processes, such as ß-oxidation and citric acid cycle (e.g., Rahn et al., 1973; Henderson, 1996). 

Based on their structural similarity the physico-chemical properties are also similar. Both substances are insoluble in water (< detection limit of used method), feature similar partition coefficients of 5.82 (CAS No. 90411-68-0) and 6.15 (CAS No. 59130-69-7) and the main components of the UVCB substances have similar molecular weights of 368.6 - 396.7 (CAS No. 90411-68-0) and 368.6 (CAS No. 59130-69-7). The volatility of both substances is low (< 0.01 Pa at 20 °C). Hence, the behaviour and fate of the substances in the environment is considered to be identical.

The non-GLP study with Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0) was conducted under aerobic conditions according to OECD guideline 301B using non-adapted, domestic activated sludge as inoculum (Bouillon, 2012). Based on CO2 evolution a mean degradation of 89.8% was observed after 29 days. According to “OECD Guidelines for the testing of chemicals – Revised introduction to the OECD guidelines for testing of chemicals, Section 3 – Part 1: Principles and strategies related to the testing of degradation of organic chemicals degradation” published by OECD (2006) the ready biodegradability data for mixtures should be evaluated carefully. For substances with different chain lengths the 10-day window should not be used for the interpretation of the results. It is possible that a sequential biodegradation occurred which might have led to a prolonged lag-Phase and therefore a slower biodegradation period. In this case the pass level can be applied at 28 days. Hence, the test substance is determined to be readily biodegradable according to OECD criteria.

Due to structural and property similarities to the analogue substance, Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0), as explained above, this results is also applicable to read across to Hexadecyl 2-ethylhexanoate (CAS No. 59130-69-7). This assumption is supported by a BIOWIN calculation for this substance (Hopp, 2011).  

A detailed reference list is provided in the technical dossier (see IUCLID, section 13) and within the CSR.