Fatty acids, C16-18, 2-ethylhexyl esters

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Methyl ester - Skin sensitisation

 

A Buehler test was performed with the read across substance methyl linoleate (CAS# 112 -63 -0) according to OECD Guideline 406 (Pittermann, 1992). Groups of 10 Dunkin-Hartley guinea pigs were treated with test substance concentrations of 40% for topical induction and 20% for topical challenge diluted in olive oil.

All test animals and negative control animals were without any distinct dermal effects after challenge. No deaths occurred and no significant differences in the gain of the body weight occurred. All tested animals, negative control animals and additional animals receiving only treatment with olive oil (vehicle control group) showed weak to moderate dermal reactions. Thus, it was concluded that the test substance itself was a non-sensitizer on the skin of guinea pigs under the given test conditions.

 

Methyl linoleate (CAS# 112-63-0) was used as a structural analogue read across substance for skin sensitisation hazard identification of ethyl linoleate (CAS# 544-35-4) and fatty acids, essential, ethyl esters (CAS# 91051-05-7). It can be expected, that methyl linoleate would exert similar characteristics in pathophysiological mechanism of skin sensitisation. Upon activity of dermal esterases, methyl linoleate would be cleaved into linoleic acid and methanol, representing sufficient similarity to the metabolites linoleic acid and ethanol, resulting from cleavage of ethyl linoleate (CAS# 544 -35 -4) and fatty acids, essential, ethyl esters (CAS# 91051 -05 -7).

 

Ethyl ester - Skin sensitisation

 

A Local Lymph Node Assay was performed with ethyl linoleate (CAS# 544-35-4) in CBA/J mice according to OECD Guideline 429 (van Otterdijk, 2010). The test substance contained besides 75% ethyl linoleate also 10% ethyl oleate (FA 18:1) as impurity.

Three experimental groups of five female/J mice were treated with test substance concentrations of 25, 50 or 100% w/w on three consecutive days, by open application on the ears. Five vehicle control animals were similarly treated, but with vehicle alone (Acetone/Olive oil (4:1 v/v)).Slight irritation of the ear skin and increased sizes of the auricular lymph nodes were observed by most animals treated at 50 and 100%. However, the ear thickness was not measured.The SI values calculated for the substance concentrations 25, 50 and 100% were 2.3, 6.6 and 8.2, respectively.

However, these test results cannot be interpreted as skin sensitising effects, as previous experiments indicated, that testing of linoleic acid and oleic acid obviously produced false positive results in the LLNA (Kreiling, 2008): The skin sensitization potential of eight unsaturated and one saturated lipid (bio) chemicals was tested in both, the LLNA and the GPMT to address the hypothesis that chemicals with unsaturated carbon–carbon double bonds may result in a higher number of unspecific (false positive) results in the LLNA compared to the GPMT. Seven substances (oleic acid, linoleic acid, linolenic acid, undecylenic acid, maleic acid, squalene and octinol) gave clear positive results in the LLNA (stimulation index (SI) P 3) and thus would require labelling as skin sensitizer. Fumaric acid and succinic acid gave clearly negative results. In the GPMT, besides some sporadic skin reactions, reproducible skin reactions indicating an allergic response were found in a few animals for four test substances. Based on the GPMT results, only undecylenic acid would have to be classified and labelled as a skin sensitizer according to the European Dangerous Substance Directive (67/548/EEC) (results for linoleic acid were inconclusive), while the other seven test substances would not require labelling. Possible mechanisms for unspecific skin cell stimulation and lymph node responses were discussed. In conclusion, the suitability of the LLNA for unsaturated compounds bearing structural similarity to the tested substances should be carefully considered and the GPMT was recommended as an accepted test method for skin sensitization hazard identification.

 

Isopropyl ester - Skin sensitisation

 

A Local Lymph Node Assay was performed with isopropyl laurate (CAS# 10233-13-3) according to OECD Guideline 429 (Stitzinger, 2010). Ear skins of 5 female CBA mice were treated with 25μL of the liquid test substance at concentrations of 25, 50 and 100% diluted with acetone/olive oil (4:1 v/v). Alpha-hexylcinnamicaldehyde was used for the six-month reliability check, indicating the sensitivity of the test method in the laboratory. Measurement of radioactivity showed significantly and dose-dependent increases of the disintegrations per minute/animal values: for the experimental groups treated with test substance concentrations 25, 50 and 100% the values were found to be 620, 1324 and 1929 DPM, respectively. The mean DPM/animal value for the vehicle control group was 375. However, concomitant erythema of the treated skin sites at test substance concentrations of 50 and 100% were observed. Thus, the results cannot be clearly verified as sensitising effects, as skin irritation could also induce an dose-dependent increase of the stimulation index. Therefore based on the study results, the test substance cannot clearly be classified as skin sensitizer.

 

A Guinea pig maximisation test was performed with isopropyl myristate (CAS# 110-27-0) similar to OECD Guideline 406 (Potokar, 1984). 15 female Pirbright-Hartley guinea pigs were treated with the test substance at 5% for intra- and epidermal induction on days 1 and 7, respectively. 19 animals served as controls. 14 days after the epidermal induction, epidermal challenging was performed with a 25% test substance dilution in 2% Carboxymethylcellulose and 0.5% Cremophor. 48 and 72 hours after challenging skin examination revealed no irritation. Thus, isopropyl myristate was found to be not sensitising to the skin of guinea pigs, when used as 5% solution for induction and 25% solution for challenge.

 

Based on the information of the interdisciplinary task force on allergy diagnostics in the metal branch, in 2001, the German Contact Dermatitis Research Group (DKG) compiled two metalworking fluid (MWF) test series with currently and previously used components, respectively (see IUCLID section 7.10.4, Geier, 2004). 251 metalworkers who were patch tested because of suspected MWF dermatitis in 2002 and 2003 were included into a retrospective data analysis. After 2 years of patch testing, the results obtained with these series were presented, based on data of the Information Network of Departments of Dermatology (IVDK). 196 patients were tested for sensitivity to a 10% dilution of isopropyl myristate (CAS# 110-27-0) in petrolatum in a human patch test according to test guidelines of the International Contact Dermatitis Research Group (ICDRG) and the DKG. None of the 196 patients showed a reaction. Therefore, isopropyl myristate was found not be a sensitizer to human skin.

 

Further human sensitisation data were available for another structural analogue read across substance: diisopropyl sebacate (CAS# 7491-02-3). Similar to the isopropyl ester members of the SCAE (C2-C8) category, this substance will be cleaved upon esterase activity into isopropanol and sebacic acid (decanedioic acid, CAS# 111-20-6).The sensitizing potential of diisopropyl sebacate (CAS# 7491-02-3) was assessed in a human volunteer study with 13 male and 42 female subjects according to the method of Marzulli and Maibach. For induction, occlusive exposure to the undiluted test substance for 48 hours, three times a week for three weeks on the back was performed. After a two week recovery period, a challenge exposure was performed under an occlusive dressing for 48 h either on the same site as the induction or another site that had never had contact with the test substance. After each induction exposure, cutaneous reactions were evaluated directly as well as 24 and 48 h after patch removal. No significant reaction attributable to sensitisation was observed in the 51 volunteers finishing the study. Only one subject showed slight irritation at day 9 of induction. Therefore, the test material at 100% when applied to the human skin was found to be not irritating and not sensitising under the test conditions.

 

Diisopropyl sebacate is a dicarboxylic acid ester containing to two isopropanol moieties and sebacid acid as dicarboxylic acid. Upon hydrolytic esterase cleavage sebacic acid and isopropanol will be formed as metabolites. These metabolites are similar to those formed by hydrolytic esterase cleavage of the SCAE C2-C8 category members. Therefore, Read Across to diisopropyl sebacate for this endpoint was judged to be justified. 

 

Butyl ester - Skin sensitisation

 

Fatty acids, C16-18 and C18-unsatd., branched and linear, Bu esters (CAS# 163961-32-8) was tested in Guinea pig maximisation test according to OECD Guideline 406 (Sanders, 2002). Reliability checks had been performed 2 times a year with 10 test and 5 control animals using alpha-hexylcinnamaldehyde and 2-Mercaptobenzothiazole as positive control substances confirming the sensitivity of the used animal strain. 20 test and 10 control animals (Dunkin-Hartley guinea pigs) were induced intradermally with the 1% test substance in arachis oil BP. The epidermal induction was performed with the undiluted test substance. The animals were challenged with 50% (10 test and 5 control animals) and 75% (10 test and 5 control animals) test substance solutions in arachis oil. 24 and 48 hours after termination of challenge exposure skin readings revealed no indications for a skin sensitising potential of Fatty acids, C16-18 and C18-unsatd., branched and linear, Bu esters.

 

Ethylhexyl ester - Skin sensitisation

 

A Guinea pig maximisation test was performed with Fatty acids, C8-16, 2-ethylhexyl esters (CAS# 135800-37-2) according to OECD Guideline 406 (Steiling, 1991). 19 test and 10 control animals (Dunkin-Hartley guinea pigs) were induced intradermally with the 5% test substance diluted in peanut oil on both sides of the spine with and without Freud's complete adjuvant. 7 days later a 40% test substance dilution was used for the epidermal induction for 48 hours. Another 14 days later the animals were challenged by epidermal induction of the sheared flank skin with test substance diluted to 20% with paraffin oil. 24 and 48 hours after termination of challenge exposure skin readings revealed no indications for a skin sensitising potential of the test substance.

 

Fatty acids, C16-18, 2-ethylhexyl esters (CAS# 91031-48-0) was tested for its skin sensitisation potential in a Guinea pig maximization test according to OECD Guideline 406 (Clouzeau, 1991). 20 test and 10 control animals (Dunkin-Hartley guinea pigs) were induced intradermally with the test substance diluted to 25% in paraffin oil. 7 days later the epidermal induction was performed with the undiluted test substance, as this concentration (100%) was found to be slightly irritating in the range finding test. 12 days after the last induction treatment the animals were challenged with a 50 % test substance solution in paraffin oil. 24 and 48 hours after termination of challenge exposure skin readings revealed no indications for a skin sensitising potential of Fatty acids, C16-18, 2-ethylhexyl esters.

 

Additional information

 

The OASIS Database provided from the Danish Environmental Protection Agency and Danish QSAR group, National Food Institute, Technical University of Denmark (DTU) was used to assess the sensitization potential of fatty acid methyl esters by QSAR prediction. The following members were all predicted to have no skin sensitization potential:

 

- Isopropyl laurate (CAS# 10233-13-3)

- Isopropyl myristate (CAS# 110-27-0)

- Isopropyl palmitate (CAS# 142-91-6)

- Isopropyl oleate (CAS# 112-11-8)

- Ethyl linoleate (CAS# 544-35-4)

- Ethyl oleate (CAS# 111-62-6)

- 2-Ethylhexyl oleate (CAS# 26399-02-0)

- Butyl stearate (CAS# 123-95-5)

 

Isopropyl laurate, isopropyl myristate, isopropyl palmitate, ethyl linoleate and butyl stearate are broadly used as leave-on cosmetics. Isopropyl laurate is used in deodorants, sunless tanning, facial moisturizer, whereas isopropyl myristate is used in foundation, moisturizer, eye shadow, concealer, lipstick, facial powder, facial moisturizer, hand cream, hand sanitizer, lip balm. Ethyl linoleate is used in the following cosmetic product types: facial moisturizer/treatment, anti-aging, moisturizer, styling gel/lotion, conditioner, facial cleanser, after shave, hair spray, sunscreen-moisturizer and shaving cream (source: www.cosmeticsdatabase.com).

 

According to the ECETOC Monograph# 32 (ISSN-0773-6347-32, Brussels, 2002) on the Use of Human Data in Hazard Classification for Irritation and Sensitisation, "no classification with R43 is necessary, where a significant number of individuals (e.g. 100,000) have frequent (daily) skin exposure for at least one year and there is a system in place to pick up complaints and adverse reaction reports, and where no or only a few isolated cases of allergic contact dermatitis are observed".

 

Based on the fact, that an eminent number of persons have daily contact with the leave-on cosmetic substances isopropyl laurate, isopropyl myristate and ethyl linoleate and at the same time there were no clinical case reports on the sensitisation potential of these three substances available, a sensitisation potential appears very unlikely.

 

Migrated from Short description of key information:
Studies on skin sensitisation were available for the following category members (CAS#): 10233-13-3 (in progress), 110-27-0, 544-35-5 (in progress), 135800-37-2, 91031-48-0 and 163961-32-8.

Justification for classification or non-classification

According to DSD (67/548/EEC) and CLP (1272/2008/EC) classification criteria for sensitisation, no classification is required.