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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

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Ecotoxicological information

Endpoint summary

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Description of key information

Additional information

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. All substances in the category have an overlap in regard to their composition. With reference to information of existing categories, the category of Dimerised Fatty Acids and Its Derivatives is based on similar physicochemical and toxicological properties and 2 sub-categories are further defined on the basis of their environmental fate and 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 ready biodegradability and other environmental fate properties.

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 through metabolic processes. In view of the results of various QSAR analyses, the toxic hazard of these substances mainly depends on the number of carbons, on the chain “structure”, such as branching, unsaturation, grade of cyclics and aggregation, as well as on their position in the whole molecular structure. In contrast, the number of the functional group “carboxylic acids” has no significant influence on the tox- and ecotoxicological profiles.

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

As aforementioned the similarity of the sub-category 2 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 the basis of overlap in composition, representative molecular structures, physico-chemical properties, tox-, ecotoxicological profiles and is 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. The key characters 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 by metabolic processes)
  • 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 >5, log Kow is judged to be > 4, insolubility in water)
  • Common properties for environmental fate & eco-toxicologcial profile of the two sub-categories (not readily biodegradable, no toxicological effects up to the water solubility limit for aquatic organisms)
  • Common levels and mode of human health related effects

Aquatic toxicity Sub-Category 2: Dimerised Fatty Acids and its derivatives, predominantly oligomers (dimer, trimers)

Aquatic toxicity: All available aquatic toxicity studies within this category showed that Dimerised Fatty Acids, predominantly oligomers are not harmful to aquatic organisms.

In accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. grouping of substance and read across approach, for Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5) is assumed to be not harmful to aquatic organisms based on the results from short-term studies of different trophic levels (fish, daphnia, algae) for the most structurally suitable read across substances within the subcategory 2 of the dimerised fatty acids category: C18-unsaturated, dimers (CAS No. 61788-89-4). The only difference between the two dimerised fatty acids, namely fatty acids, C-18 unsaturated, dimers (CAS No. 61788-89-4) and fatty acids, C-18 unsaturated, dimers, hydrogenated (CAS No. 68783-41-5) is the degree of saturation or hydrogenation, respectively. Derived from the same starting substance both have a homologous composition of fatty acids with a mainly C18 carbon chain in diverse forms. Both sub-category 2 members have a low water solubility (<0.52 mg/L), and are not readily biodegradable.

In particular, short term tests with freshwater and marine species of three trophic levels (fish: Danio rerio and Cyprinus carpio), Daphnia magna, algae (Pseudokirchnerella subcapitata)) are available for Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4), which can be used as read-across for the hydrogenated dimer. All organisms did not show any effects up to the limit of water solubility (< 0.12 mg/L, detection limit) of the tested substance. These results are supported by data within the category, and in particular by a fish long-term test with Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68743-41-5), which shows no effetcs to Danio rerio within the water solubility of the substance.

Furthermore, from the toxicity control of the 301 B Biodegradation screening test, which attained 55.7 % degradation after 28 days of incubation, it can be assumed that the substance is non-inhibitory to microbial organisms.

Finally it can be seen from the toxicity test with a water accommodated fraction of Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4) with Pseudomonas putida bacteria that no effects up to 10000 mg/L (nominal) were observed.

Since all members of the sub-category 2 (predominantly oligomers) are poorly soluble (<0.52 mg/L) and taking into account that neither Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4) did show any effects within the water solubility of the tested substances nor did the test substance itself in a long-term test with fish (Danio rerio), Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5) can therefore be regarded as not harmful for aquatic organisms.