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Biodegradation in water: screening tests

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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) Degradation of fatty acids: 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 and octanoic acid salts are readily biodegradable (80.2-86.2% in 28 days, Simon et al., 2012), 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, an accumulation in the environment is not expected (Health Canada, 2017).

(II) Available data indicate that all (fatty acid salt) chain lengths up to and including C18 can be metabolised under aerobic conditions and can be considered to be readily biodegradable (referenced in HERA, 2003; cf. table below). Regarding the group of C8 -10 fatty acids, available studies, although very limited, show that this group is readily biodegradable with degradation percentages from 100% (only one reference, which used C8-18). “Because the rate of metabolism decreases with chain length and degree of saturation, degradation results for e.g. C18 fatty acids can be considered worst-case” (HERA, 2003) and thus, serve as conservative estimate for fatty acids of a alkyl chain length from C8 -10.

(III) Anaerobic degradation of fatty acids: The aliphatic acids also undergo biodegradation under anaerobic conditions (HERA, 2003), which is supported by the fact that the above-described beta-oxidation may also proceed in the absence of oxygen (Madsen et al. 2001).

 

Identification of degradation products

Regarding the identification of degradation products, fatty acids are readily and completely broken down to carbon dioxide and water in soil and water. Hence, based on the chemical structure, transformation products of environmental concern are not expected.

 

Table: Percentages of degradation of fatty acids of various chain lengths obtained via aerobic sludge digestion tests

Fatty acid

Test

% Degradation

Reference

C8-18

BOD test, 28 d

100

Steber and Berger 1995 referenced in Madsen et al. 2001

C10

Closed bottle test, 30 d

71 - 100

*

C10

BOD test, after 1 d

23.4

*

C10

Not stated, after 5 d

60.9

*

C12

BOD test, 30 d

87

*

C12-14

CO2 Evolution, 28 d

84

*

C12-14

Closed bottle test, 28 d

90 – 94

Steber and Berger 1995 referenced in Madsen et al. 2001

C12-14

Modified OECD screening test, 28 d

91

Steber and Berger 1995 referenced in Madsen et al. 2001

C14

Closed bottle test, 28 d

85

*

C14

EMPA test, after 15 d

99

*

C16

BOD test, 28 d

100

Steber and Berger 1995 referenced in Madsen et al. 2001

C16-18

Closed bottle test, 28 d

62

*

C16-18

Closed bottle test, 28 d

77

Steber and Berger 1995 referenced in Madsen et al. 2001

C16-18

Closed bottle test, 28 d

91

Painter 1992 referenced in Madsen et al. 2001

C16-18

Modified OECD screening test, 28 d

85 – 88

Steber and Berger 1995, Painter 1992 referenced in Madsen et al. 2001

C18

CO2 Evolution, 28 d

82

*

C18

Closed bottle test, 28 d

89

*

C18

Closed bottle test, 28 d

62

*

C18

BOD test, 28 d

79

Steber and Berger 1995 referenced in Madsen et al. 2001

C20-22

Closed bottle test, 28 d

89

*

C22

BOD test, 28 d

69

Steber and Berger 1995 referenced in Madsen et al. 2001

 *OECD SIDS 2014 and references therein

In summary, fatty acids are not persistent in water, and transformation products of environmental concern are also not expected. Available data point to a ready biodegradability of fatty acids with a chain length of C8 and C10. Thus, performing additional biodegradation tests 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

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

Madsen et al. (2001). Environmental Project No. 615 Miljøprojekt, Centre for Integrated Environment and Toxicology; CETOX. Environmental and Health Assessment of Substances in Household Detergents and Cosmetic Detergent Products, p. 240.

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

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)


 

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

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