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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

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The Dimerised Fatty Acids and its Derivatives category covers C16 - C18 unsaturated fatty acids derived monomers, dimers and trimers, as well as their hydrogenated products in different proportions and in accordance with their corresponding production and purification processes. They are all prepared by the dimerisation of C16 - C18 unsaturated fatty acids. As UVCB substances derived from natural sources, members of this category are chemically similar as they are all essentially a complex mixture of C16 - C18 unsaturated and saturated, branched and linear fatty acids, their monomers, dimers and trimers with varying structural geometric isomers. In the category family, all substances have an overlap in regard to their composition. With reference to information of existing category, the category of Dimerised Fatty Acids and Its Derivatives is based on similarities in physicochemical and toxicological properties and 2 sub-categories were further defined on the basis of their environmental fate and environmental toxicity. The first sub-category covers three monomeric (by-) products of the dimerization process (readily biodegradable substances). The second sub-category covers the predominately oligomers (dimeric and trimeric products) of dimerization based on their lack of biodegradability and the environmental fate.

Sub-category 1: predominantly monomers

ID No.


Common Name

Chemical Name



Monomer acid

Fatty acids, C16-18 and C18-unsaturated, branched and linear,



Hydrogenated monomer acid

Octadecanoic acid, branched and linear”




Isooctadecanoic acid

Sub-category 2: predominantly oligomers (dimers, trimers)

ID No.


Common Name

Chemical Name



Crude dimer

Fatty acids, C16-C18 and C18-unsaturated, dimerized




Fatty acids, C18-unsaturated, dimers



Hydrogenated dimer

Fatty acids, C18-unsaturated, dimers, hydrogenated




Fatty acids, C18-unsaturated, trimers

Derived from the same starting substance, all substances in this category have a homologous composition of fatty acids with a C16 - C18 carbon chain in diverse forms, that is susceptible to oxidation of metabolic process. In view of the results of various QSAR analyses, the toxic hazard of the substances mainly depends on the number of the carbons, on the chain “structure”, such as branching, unsaturation, grade of cyclics and aggregation, as well as their position in the molecular structures. Whereas, the number of the function group “carboxylic acids” has no significant influence on the tox- and ecotoxicological profiles.

Sub category 1: predominantly monomers

As aforementioned, the similarity of category members is justified, in accordance with the specifications listed in Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances and read across, on basis of scope of variability and overlapping of composition, representative molecular structure, physico-chemical properties, tox-, ecotoxicological profiles and supported by various QSAR methods. There is no convincing evidence that any one of these chemicals might lie out of the overall profile of this sub-category, respectively

The key points that the members share are:

  • Common origin of C16-18 unsaturated fatty acids
  • Similar/overlapping structural features (no hydrolysable groups, all members have a homologous composition of fatty acids with a C16 - C18 carbon chain in diverse forms, that are susceptible to oxidation of metabolic process)
  • Similar metabolic pathways (same ADME pathways of fatty acids, absorbed fatty acids undergo rapid metabolism (via ß- or ω-oxidation) and excretion either in the expired CO2 or as a hydroxylated or conjugated metabolite in the urine in the case of cyclic fatty acids)
  • Similar physico-chemical properties (log Koc > 4 < 5, the log Kow is judged to be > 4, the poor solubility in water)
  • Common properties for environmental fate & eco-toxicologcial profile of the two sub-categories (readily biodegradable, no toxicological effects up to the water solubility limit for aquatic organisms)
  • Common levels and mode of human health related effects

The aquatic toxicity of the monomers, and in this case in particular Fatty Acids, C16-18 and C-18, unsaturated, branched and linear has been assessed with short-term tests with freshwater species of three trophic levels (fish, Daphnia, algae) and a long-term test with Daphnia magna, which are available for the substance itself. Organisms on all trophic levels did not show any effects within the water solubility of the tested substance. The same applies for microorganisms, where tests with Pseudomonas putida bacteria showed no effects up to the limit of the water solubility of Fatty Acids, C16-18 and C-18, unsaturated, branched and linear.

As there was no sign that fish are more sensitive than aquatic invertebrates in the short term tests, it cannot be expected that a long-term test with fish will generate different results than a long-term study on aquatic invertebrates, therefore as part of an integrated testing strategy a long term study on fish is not required unless otherwise triggered.

In conclusion, the available data, covering three trophic levels and taking into account both acute and chronic effects, enables a reliable risk assessment of the sub-category 1 predominantly monomers, and no further testing is needed. Based on the available data the members of the Dimerised Fatty Acids and its derivatives can be regarded as not harmful for aquatic organisms.