Fatty acids, C18-unsatd., dimers

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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.	CAS No.	Common Name	Chemical Name
#5	68955-98-6	Monomer acid	Fatty acids, C16-18 and C18-unsaturated, branched and linear
#6	68201-37-6	Hydrogenated monomer acid	Octadecanoic acid, branched and linear
#7	30399-84-9		Isooctadecanoic acid

 

Sub category 2: predominantly oligomers (dimers, trimers)

ID No.	CAS No.	Common Name	Chemical Name
#4	71808-39-4	Crude dimer	Fatty acids, C16-C18 and C18-unsaturated, dimerized
#1	61788-89-4	Dimer	Fatty acids, C18-unsaturated, dimers
#3	68783-41-5	Hydrogenated dimer	Fatty acids, C18-unsaturated, dimers, hydrogenated
#2	68937-90-6	Trimer	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 judged to be > 4, insolubility in water)
• Common environmental fate & eco-toxicologcial profile of the two sub-categories (not readily biodegradable, no toxicological effects up to the water solubility limit)
• 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.

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). All organisms did not show any effects up to the limit of water solubility (<0.12 mg/L, detection limit) of the tested substance. 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.

These short-term toxicity results are supported by long-term toxicity data within the category, and in particular for Fatty acids, C18 -unsaturated, dimers, hydrogenated (CAS No. 68743-41-5). In a long term test with fish (Danio rerio) no effects were observed within the water solubility of the substance. Both Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4) and Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5) are derived from Fatty acids, C16-18 and C18-unsaturated, dimerised (CAS No 71808-39-4), the crude dimer. The only difference between the two “dimer acids” is the degree of saturation or hydrogenation. Data from the MITI-database (MOE, 2003; MOE, 2008) indicate for C16/C18 fatty acids a slightly higher toxicity of unsaturated forms than the saturated forms, however this MITI data also shows that the length of the chain is correlated to the level of toxicity. For dimerised C18 chains resulting in 36 carbon molecules, i.e. a duplication of C atoms, this is directly reflected by the very low water solubilities (both < 0.52 mg/L). As the C16-and C18 fatty acids are in general more water soluble than dimerised fatty acids it is not expected that effects will occur up to the limit of water solubility regardless of the level of saturation and thus read across for to the C36 saturated form to the unsaturated form is fully valid.

Since all members of the sub-category 2 (predominantly oligomers) are insoluble (< 0.52 mg/L, limit of detection) and taking into account that all tests carried out with freshwater and marine species of three trophic levels (fish, Daphnia, algae) for substances within the category did not show any effects within the water solubility of the tested substances, neither in short- nor in long-term tests, the category members of Dimerised Fatty Acids and Its Derivatives and therefore also Fatty acids, C18-unsaturated, dimers (CAS No. 61788-89-4) can be regarded as not harmful for aquatic organisms.

References:

Ministry of the Environment, Government of Japan (2003). Daphnia magna, reproduction test by oleic acid. Food Research Laboratories. Report No. 14053. 2003-03-31.

Ministry of the Environment, Government of Japan (2008). Daphnia, reproduction toxicity test for palmitic acid. Mitsubishi Chemical Safety Institute Ltd.,Laboratory. Report No. A050381. 2008-02-14.