Docosanoic acid

Endpoint summary

Additional information

Justification for grouping of substances and read-across

The Fatty acids category covers aliphatic (fatty) acids, which all contain the carboxylic acid group attached to an aliphatic acid chain. The category contains mono-constituent substances and UVCB substances being compositions of these substances.

 

Mono-constituent substances are predominantly saturated, even-numbered acids, in the carbon range C6 to C22. Other mono-constituent fatty acids include:

- odd-numbered acids: heptanoic acid C7 and nonanoic acid C9;

- unsaturated acids: elaidic acid C18:1, oleic acid C18:1, linoleic acid C18:2, conjugated linoleic acid C18:2, linolenic acid C18:3 and erucic acid C22:1;

- dicarboxylic acids: azelaic acid C9d and sebacic acid C10d.

 

In accordance with Article 13 (1) of Regulation (EC) No 1907/2006, "information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met.” In particular, information shall be generated whenever possible by means other than vertebrate animal tests, which includes the use of information from structurally related substances (grouping or read-across).

Having regard to the general rules for grouping of substances and read-across approach laid down in Annex XI, Item 1.5, of Regulation (EC) No 1907/2006, whereby substances may be considered as a category provided that their physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity, 40 substances are allocated to the category of Fatty acids.

 

Grouping of substances into this category is based on:

(1) common functional groups: all members of the Fatty acids category are carboxylic acids with a linear aliphatic tail (chain), which is either saturated or unsaturated. The carbon chain lengths varies between C6 and C22 (uneven/even-numbered); and

(2) common precursors and the likelihood of common breakdown products via biological processes, which result in structurally similar chemicals: the members of the Fatty Acids category result from the hydrolysis of the ester linkages in a fat or biological oil (both of which are triglycerides), with the removal of glycerol. Fatty acids are almost completely absorbed after oral intake by the intestinal mucosa and distributed throughout the body. Fatty acids are an energy source. They are either re-esterified into triacylglycerides and stored in adipose tissues, or oxidized to yield energy primarily via the β-oxidation pathway. The excretion products are carbon dioxide and water after metabolism; and

(3) constant pattern in the changing of the potency of the properties across the category: the available data show similarities and trends within the category in regard to physicochemical, environmental fate, ecotoxicological and toxicological properties. For those individual endpoints showing a trend, the pattern in the changing of potency is clearly and expectedly related to the length of the fatty acid chains.

A detailed justification for the grouping of chemicals and read-across is provided in the technical dossier (see IUCLID Section 13).

 

Environmental fate of the Fatty acids category

The data set for biodegradation includes experimental biodegradation studies as well as data obtained by QSAR. As summarized in the category justification, the members of the fatty acid category can be regarded as readily biodegradable since the vast majority of the experimental results revealed ready biodegradability which was supported by reliable QSAR predictions. The consistent positive test results over the whole category supersede single negative results. In conclusion, aliphatic fatty acids comprising C6-C22 carbon chain length are judged to be readily biodegradable. This judgment is consistent with the hazard assessment presented in the OECD SIDS (2009) for the category “Aliphatic Acids Category” where aliphatic fatty acids with a carbon chain length in the range of C6 – C22 were described to be readily biodegradable. Hydrolysis is not a relevant degradation pathway for these substances, due to their ready biodegradability and/or their poor water solubility.

The range of log Kow values in the category suggests that fatty acids with chain lengths greater than C12 may be expected to have tendency of a higher bioaccumulation. However, this takes into account physicochemical properties of chemicals and only indicates their intrinsic potential, but not its behaviour in the environment (not considering, e.g., biodegradation), and in living organisms (not considering, e.g. metabolism). Fatty acids are naturally stored in form of triacylglycerols primarily within fat tissue until they are used for energy production and therefore fatty acids are considered to present no risk to aquatic organisms with respect to the bioconcentration or biomagnification.

Within the fatty acids category the Koc values increase with increasing chain length and decreasing water solubility as well, in which fatty acids with a chain length greater than C12 shows values above log Koc < 3 indicating potential for adsorption to solid organic particles, whereas fatty acids with a chain length of C12 and smaller are unlikely to adsorb to sediment. Nevertheless, all substances are readily biodegradable, indicating that persistency in the environment (water phase, sediment or soil) is not expected.

The volatilization potential of the Fatty acids category members is negligible (Vapour pressure < 5.6 Pa at 25 °C). Nevertheless, if released into the atmosphere, the substances are expected to be rapidly photodegraded in view of their estimated half-lives in air, ranging from 0.892 to 23.24 hours (calculation with AOPWIN 1.92). Based on the above information, accumulation in air, subsequent transportation through the atmosphere and deposition into other environmental compartments is not anticipated.

 

Ecotoxicological properties of the Fatty acids category

Acute toxicity data for fatty acids with a carbon chain length of C12 - C22 showed no effects to fish, invertebrates and algae up to the limit of water solubility. Furthermore, chronic toxicity effects towards fish and algae were not observed up to the limit of water solubility. Data concerning chronic toxicity effects on invertebrates are available for limited substances, due to major methodological difficulties during testing some tests could not be taken into account for the hazard evaluation. Therefore, a read across approach was applied within the fatty acids with a carbon chain length from C10 up to C22 from longer to shorter carbon chain length fatty acids and vice versa. A test program in cooperation with the Fraunhofer Institute is ongoing, designed to overcome methodological deficiencies and evaluate the long-term environmental hazard of the substances to aquatic invertebrates. Studies with different fatty acids (mono-constituents as well as UVCBs) on chronic invertebrate toxicity are still ongoing within the frame of this program.

Toxicity on microorganisms was not observed for fatty acids independent from carbon chain length.

 

Aquatic toxicity of docosanoic acid (CAS 112-85-6)

Studies on the acute aquatic toxicity of docosanoic acid are available for all three trophic levels (fish, invertebrates and algae), resulting in no effects up to the limit of water solubility. Furthermore, a prolonged fish study conducted with O. latipes for 14 days (OECD 204) is available for docosanoic acid. Since this test is not sufficient for hazard assessment regarding current regulations, chronic fish toxicity data from a surrogate substance, sodium laurate (CAS 629-25-4, C12) is taken into account. In this study Danio rerio were exposed for 28 d to sodium laurate in a flow-through fish test. From this test it can be concluded, that long-term effects on fish up to the limit of water solubility of docosanoic acid are also not to be expected. Long-term toxicity data on invertebrates (OECD 211) is available for docosanoic acid showing no chronic effects on reproduction to D. magna up to the limit of water solubility. Furthermore, no chronic effects on aquatic algae of docosanoic acid are observed up to the limit of water solubility in one study with S. capricornutum according to OECD 201.

For microorganisms no toxic effects are expected based on read across data from stearic acid (CAS 57-11-4).