Fatty acids, C8-10, zinc salts

Biodegradation in soil

Description of key information

The assessment entity “C8-10” refers to the anions of common saturated fatty acids with an alkyl chain length of C8 (octanoic/caprylic acid) and C10 (decanoic/capric acid). In addition to data available on octanoic acid and decanoic acid, the endpoint is addressed with publicly available data on fatty acids with the same or similar structure, including fatty acids with longer alkyl chain lengths if relevant and appropriate in accordance with previously applied read-across approaches (U.S. EPA Fact Sheet, 2008).

A registration dossier shall contain information on the environmental hazard assessment (Regulation 1907/2006, Article 10). For the environmental hazard assessment of fatty acids (C8-10), the standard testing regime set out in Annexes VII to IX is adapted in accordance with Section 1.2 and 1.3 of Annex XI so that “testing does not appear to be scientifically necessary” as follows:

(I) Fatty acids will be rapidly degraded in soil and water via the β-oxidation pathway and are thus not expected to accumulate in the environment (EU RAR zinc distearate, 2008). Octanoic acid (C8) and fatty acids up to a chain length of C10 are readily biodegradable (i.e. octanoic acid, zinc salt, basic: 80.2-86.2% in 28 days, Simon et al., 2012; OECD SIDS 2014), do not bioaccumulate (Kow < 4, BCF < 56.2 (modelled); OECD SIDS 2014) and are not expected to persist in the environment due to a quick microbial degradation. In addition, half-lives of fatty acids salts with a chain length of C8-10 in surface waters were reported with < 25 h for starting concentrations of 7.3-24.7 mg/L (Yoshimura et al., 1984 as cited in HERA RA 2003). Hence, bioaccumulation in the environment is not expected (Health Canada, 2017).

(II) In addition, half-life times of salts of C8- C18 fatty acids in soil were determined with < 3 days (U.S. EPA Fact Sheet, 2008, Health Canada, 2017) and the salts are thus broken down readily by soil microorganisms (Health Canada, 2017). Hypothetically, the aerobic degradation pathway of fatty acids constitutes a sequential elimination of C2 fragments, meaning that major soil metabolites of a given fatty acid would be other fatty acids with shorter chains (U.S. EPA Fact Sheet, 2008). Fatty acids are therefore not expected to be persistent in the environment (Health Canada, 2017). In summary, QSAR-based estimates and a ready biodegradability indicate a low bioaccumulation potential for fatty acids.

Thus, performing further studies on biodegradation of octanoic and decanoic acid in soil is not expected to provide more insight into the environmental fate and is not considered necessary for the environmental hazard assessment.

References:

OECD SIDS initial assessment profile- aliphatic acids (2014), CoCAM 6 September 30-October 3, Italy/ICCA, p. 41

HERA (2003). Human & Environmental Risk Assessment on ingredients of European household cleaning products. Fatty Acid Salts (Soap) Environmental Risk Assessment

Health Canada’s PMRA, Pest Management Regulatory Agency (2017). Ammonium Salt of Fatty Acid Proposed Registration Decision PRD2017-04, p. 36

Simon, M. (2012). Manometric respirometry test: Ready biodegradability of octanoic acid, zinc salt, basic (CAS 90480-58-3 by activated sludge. Study report: Fraunhofer Institute for Molecular Biology and Applied Ecology (IME)

EU Risk Assessment Report, RAR - Zinc distearate (2008), CAS No. 557-05-1 & 91051-01-3. PART 1 Environment, p. 63

U.S. Environmental Protection Agency, U.S. EPA (2008). Ammonium nonanoate (031802) Fact Sheet, OPP Chemical Code: 031802, p. 2