Fatty acids, dehydrated castor-oil

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).

Fatty acids are ubiquitous and dynamic in the environment and are completely metabolised in water and soil by microorganisms. Fatty acids occur in the environment both naturally and from the use by man. Microbial metabolism is the primary route of degradation in the environment and fatty acids are an integral part of the cell membranes of every living organism from bacteria and algae to higher plants and animals. Each of these organisms contains fatty acids also as part of their food reserves and they also consume fatty acids to produce energy required for anabolic and catabolic metabolism. 

In water fatty acids are abiotically stable (OECD SIDS, 2009). Based on the ready biodegradability or high insolubility and molecular structure (aliphatic, mostly saturated carbon chains) hydrolysis is not a relevant degradation pathway and thus was not tested. Modelled data on the photodegradation in air are available for aliphatic fatty acids of C6-C22 carbon chain length. The data show a decreasing photodegradation half-life with increasing chain length. Unsaturated fatty acids undergo photolysis faster than saturated. The half-life declines with the number of double bounds. The calculated half-lives are in the range of 0.892 - 0.998 hours for 9,12-Octadecadienoic acid, (Z,Z) (C18, 2 double bonds) to 23.236 hours for hexanoic acid (C6) (OECD SIDS, 2009). Direct photolysis is not expected to contribute appreciably to the overall breakdown rate in water and soil, since the environmental degradation of these substances is predominantly of biotic nature.
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.
Adsorption potential to sediment and soil is shown for fatty acids starting at a chain length of 12 and higher indicated by a Koc value of approximately 500 for lauric acid (C12). Accordingly, fatty acids with a shorter chain length partition mainly to the water phase. The members of the fatty acids category with chain length greater than 14 have a low potential of mobility in soil based on high Koc values and low water solubility. Volatilisation is not expected to be a significant transport process or dissipation route for fatty acids in the environment.The log Pow of fatty acids are in the range of 1.57 to 9.91. This suggests that some fatty acids may tend to bioconcentrate in the environment. 

A fish bioaccumulation study is available for a C12 fatty acid-sodium laurate which showed negligible evidence of bioaccumulation potential in fish tissues with an BCF of 255 L/kg after 28 days exposure.
As fatty acids are naturally stored in the form of triacylglycerols primarily within fat tissue until they are used for energy production (fat storage tactic), it is therefore considered that there will be no risk to aquatic organisms from bioconcentration/biomagnification of fatty acids within the food chain.
Similarly the range of log Koc values given suggests that some fatty acids may be expected to adsorb to sediment. It is considered that rapid biodegradation and the ubiquity of fatty acids will not have any environmental relevance. Therefore it is considered that there will be no risk to sediment dwelling organisms.