Hexanoic acid, 2-ethyl-, C16-18-alkyl esters

Toxicity to soil microorganisms

Additional information

One study investigating the short-term toxicity to earthworm of Hexanoic acid, 2 -ethyl, C16 -C18 alkyl ester (CAS 90411 -68 -0) is available. The study was performed as a limit test according to OECD guideline 207 and GLP (Harris, 2013). The test organism Eisenia fetida was exposed to the test substance in artificial soil for 14 days, at the nominal test concentration 1000 mg/kg. No mortality occurred during the test period. Hence, the test substance is not expected to have effects on soil macroorganisms. No further studies on terrestrial organisms are available for this substance. However, due to the ready biodegradability of the substance only negligible amounts, if at all, are expected to be present in the terrestrial compartment. Therefore chronic exposure of terrestrial organisms is unlikely. Furthermore, the substance is not toxic to aquatic organisms up to the limit of water solubility. In addition, available data indicate, that Hexanoic acid, 2-ethyl-, C16-18 alkyl esters is not bioaccumulative. Based on the available information, toxicity to terrestrial macroorganisms is not expected to be of concern.

Intrinsic properties and fate/ exposure

Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0) is readily biodegradable (90% CO2 evolution in 28 days; Bouillon, 2012). According to the Guidance on information requirements and chemical safety assessment, Chapter R.7b, readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs) (ECHA, 2012b). Therefore, after passing through conventional STPs, only low concentrations of these substances are likely to be (if at all) released into the environment.

Furthermore, the substance exhibits a log Koc value of > 5 and is poorly water soluble (< 0.15 mg/L measured in aqua dest). The Guidance on information requirements and chemical safety assessment, Chapter R.7b (ECHA, 2012b) states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will get in contact with activated sludge organisms. Nevertheless, once this contact takes place, these substances are expected to be removed from the water column to a significant degree by adsorption to sewage sludge (Guidance on information requirements and chemical safety assessment, Chapter R.7a, ECHA, 2012a) and the rest will be extensively biodegraded (due to ready biodegradability). If direct/indirect application of the substances occurs (indirect via sludge application) will occur, the substance will again be rapidly degraded until ultimate biodegradation.

Aquatic and terrestrial ecotoxicity data

Acute and chronic aquatic toxicity tests of the substance Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0) and the analogue substances C8-16-Fatty acid-2-ethylhexyl ester (CAS No. 135800-37-2) and 2-Ethylhexyloleat (CAS No. 26399-02-0) to fish, invertebrates, algae and microorganisms showed no adverse effects occurred. The obtained results indicate that Hexanoic acid, 2-ethyl-, C16-18 alkyl esters is likely to show no toxicity to soil organisms as well.

Metabolisms/Bioaccumulation

After absorption, Hexanoic acid, 2-ethyl-, C16-18 alkyl esters is expected to be enzymatically hydrolysed in vivo by the ubiquitary enzyme carboxylesterase, yielding the corresponding alcohols and 2-ethylhexanoic acid. QSAR estimations using BCFBAF v3.0 support the expected rapid biotransformation of this substance with BCF/BAF values of < 130 L/kg, respectively (Arnot-Gobas estimation including biotransformation, upper trophic level).

The metabolism of the hydrolysis products: alcohol (i.e. C16/C18 fatty alcohols) and 2-ethylhexanoic acid is well established and not of concern in terms of bioaccumulation (for further information see chapter 5.3 of the technical dossier).

Summarizing, Hexanoic acid, 2-ethyl-, C16-18 alkyl esters (CAS No. 90411-68-0) is expected to be rapidly hydrolyzed to 2-ethylhexanoic acid and C16/C18 fatty alcohols. Both hydrolysis products are supposed to be satisfactory metabolized in organisms and are not bioaccumulative. Therefore, no potential for bioaccumulation is to be expected.

Conclusion

Hexanoic acid, 2-ethyl-, C16-18 alkyl esters is unlikely to pose a risk for terrestrial organisms based on a) the lack of chronic exposure due the ready biodegradation and b) the low toxicity as expected for this substance for terrestrial organisms based on metabolism considerations and the lack of adverse effects in aquatic and terrestrial ecotoxicity tests. Therefore, no further tests on terrestrial organisms are provided.

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