Zinc dioctanoate

Biodegradation in water: screening tests

Description of key information

The assessment entity “C8 -Octanoate” is the anion of a common saturated C8- fatty acid (octanoic/caprylic acid), present in e.g. the milk of various mammals as well as palm kernel and coconut oil. The endpoint is addressed with publicly available data on fatty acids with the same or a similar structure, including conservatively fatty acids with a shorter chain(i.e. C6) 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 octanoic acid, the standard testing regime set out in Annexes VII 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) The ecotoxic potential of the fatty acid (octanoic acid) is assumed to be negligible. Fatty acids are generally not considered to represent a risk to the environment, which is reflected in their exemption from the obligation to register (Annex V, Section 9 and Regulation (EC) No 987/2008).

(II) Degradation of fatty acids:

The degradation of fatty acids proceeds by ẞ-oxidation under stepwise shortening of the alkyl chain and the formation of acetyl coenzyme A fragments, used in living cells for energy production (referenced in Madsen et al. 2001). According to HERA (2003) and references therein, the fate of fatty acid salts in aqueous systems proceeds as follows: (1) The biodegradation rate mainly depends on e.g. solubility, adsorption and physico-chemical properties. (2) The fate of fatty acid salts is strongly influenced by the poor water solubility of the calcium and magnesium salts. (3) The rate of metabolism decreases as chain length increases. (4) Unsaturation increases the rate of metabolism although the degree of unsaturation and positioning of double bonds is not highly significant and (5). The 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). “Biodegradability did not appear to be influenced by even or odd chain length, degree of saturation or unsaturation or branching” (OECD SIDS, 2014). “Biodegradation studies or model estimations for single and multi-component aliphatic acids generally confirm that the extent of biodegradation observed in 28 days meets the ready biodegradability criterion (> 60 %). In some cases, insufficient sampling points were included in the tests to determine whether or not the 10-day window was met and thus are insufficient to demonstrate ready biodegradability. When the 10-day window was not met or less than 60 % biodegradation was observed in 28 days, it is likely that the aliphatic acids tested were not fully in solution (OECD SIDS, 2014). Degradation results obtained for fatty acids of various chain lengths are summarized in the Table “Percentages of degradation of fatty acids of various chain lengths obtained via aerobic sludge digestion tests” below. Regarding the group of C8 fatty acids, the results, although very limited, show that this group is ready 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 caprylic acid (i.e. C8- fatty acid).

(III) Degradation of fatty acid salts:

The ready biodegradability of fatty acids as such can nevertheless be inhibited by the formation of insoluble salts (e.g. calcium, magnesium) that are not readily biodegradable (EU RAR zinc distearate, 2008). Former studies using the Warburg method (O2 uptake) indicate that oxidation of fatty acid salts exceeded 50%ThOD in many cases within 6-24 hours and the following conclusions were drawn for the degradation of fatty acid salts: “(1) Fatty acids sodium salts of C10-C18 can be metabolised in aerobic systems. The equivalent length calcium salts can also be metabolised, particularly if the insoluble particles are dispersed. (2) Metabolism was influenced by solubility. (3) The rate of metabolism decreased as chain length increased and (4) Unsaturation increases the rate of metabolism although the degree of unsaturation and positioning of double bonds was not highly significant” (referencedin HERA, 2003).

(IV) 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 ẞ-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 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.

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 caprylic acid under aerobic conditions. Thus,performing further biodegradation tests of octanoic/caprylic acid(C8- fatty acid) is from a scientific point of view not expected to provide more insight into the environmental fate and is not considered necessary for the environmental hazard assessment.

 

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

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

 

 

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable