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EC number: 204-677-5 | CAS number: 124-07-2
Skin irritation (OECD 404): corrosive Eye irritation (OECD 405), 70%: irritating
b: exposed skin brownish
n: skin necrotic
e: eschar formation
Table 2: Clinical signs of toxicity
Time after application
1 – 72 h
no specific findings
4 – 6 days
7 – 9 days
48 h – 6 days
1 h – 24 h
4 – 5 days
6 and 8 days
9 – 11 days
Table 3: Absolute body weight (kg)
start of study
72 h post application
end of observation period
Skin irritation after application of octanoic acid was investigated in a GLP-study performed according to OECD guideline 404. 0.5 mL of 100% octanoic acid was applied to the clipped skin of three New Zealand White rabbits under semi-occlusive conditions for 4 hours (1984). The resulting mean scores over 24, 48 and 72 hours after application were 3.0 and 1.8 for erythema and edema, respectively. The also observed light-brown staining of the skin proved to indicate skin necrosis, since a crust had formed 48 h after exposure. In each of the animals the hairs failed to grow on day 7 after treatment, showing that the dermis was affected in the deep. After the formation and loosening of the crust, the skin had almost returned to normal 14 days after exposure in the two animals, while the third animal showed a rather scurfy skin and only partial restoration of hair growth. Based on the findings, octanoic acid has to be considered as corrosive.
To determine the level of primary skin irritation of octanoic acid under occluded conditions, 0.8 mL of octanoic acid at concentrations of 30%, 50%, 60%, 70% in PEG200/H2O and 100% was applied to the clipped skin of 6 New Zealand White rabbits under occlusive conditions for 3 hours (1981a). While the mean scores for 24 and 48 hour readings were both 0 for erythema and edema after application of 30%, 50%, 60%, 70% octanoic acid, respectively, the scores were 3.3 for erythema and 3.2 for edema for 100% octanoic acid, respectively.
In another closed patch test by the same author, octanoic acid at concentrations of 4%, 7.5%, 10%, 15% and 100% was tested by applying 0.4 mL to the clipped skin of 6 white rabbits under occlusion for 3 hours (1981b). The resulting mean scores for erythema and edema were all 0 for the dilutions of octanoic acid. At 100%, the resulting mean scores were 3.3 and 2.5 for erythema and edema, respectively.
The irritation after repeated administration was investigated in a study, where five New Zealand White rabbits received applications of 0.8 mL octanoic at concentration of 55%, 60% 65% and 80% to the clipped skin under occlusion for 3 hours/day on 7 consecutive days (1981c). Based on the scores for erythema and edema the primary irritation index was calculated with the combined scores for 30 min and 21-hour post-treatment readings. The scores were 0.03, 0.03, 0.7, and >0.3 for 55%, 60%, 65% and 80% octanoic acid, respectively.
Possible corrosive properties were evaluated in a GLP - in vitro test, where discs of freshly prepared rat skin were exposed to 150 µL of octanoic acid for 24 hours followed by a measurement of the transcutaneous electrical resistance (TER) (1994). Based on the significant reduction in the measured mean resistance of the skin, the authors concluded that octanoic acid displays properties characteristic of those substances which may be corrosive to animal skin in vivo.
Whittle et al. published results of two in vitro tests on rat and human skin (1996). The experiments with rat skin were performed similar to OECD guideline 430. 150 µL of octanoic acid was added to the epidermis of each freshly prepared rat skin disc for 24 hours. After washing, the resistance measurements were conducted and resulted in a TER of 2.5 kΩ. Since the TER decreased below 5 kΩ, octanoic acid is considered to be corrosive to rat skin.
In the experiments with human skin, human skin samples (waste material obtained from mammary cosmetic surgery, 9 donors) were also exposed to 150 µL of octanoic acid for 24 hours. Tissue treated with distilled water served as concurrent control. For none of the nine donors the TER was decreased below the threshold value of 11 kΩ. According to these results, octanoic acid is considered to be non-corrosive to human skin.
In summary the available data indicate that octanoic acid has to be regarded as corrosive to skin, while concentrations <=70% did not lead to any skin irritation.
In a published study performed according to national guidelines, octanoic acid was instilled into the eyes of six rabbits and considered as eye irritant. Corneal opacity and moderate conjunctivitis did not subside in 72 h (Briggs et al., 1976). Due to the limited information, this study does not provide sufficient data for hazard assessment.
The eye irritation potential by octanoic acid at a concentration of 70% was examined in a GLP study according to OECD guideline 405. 0.1 mL of 70% octanoic acid in vaseline was instilled into one eye each of 3 female New Zealand White rabbits (2011). The untreated left eye of each animal served as control. After 24 h the eyes were rinsed. The eye reactions were examined 24, 48 and 72 h after application and every 24 h thereafter for up to 11 days. Under the conditions of the test, a single ocular application produced irritant effects in the rabbits, which were fully reversible within 6-11 days. The mean scores for corneal opacity, iris, conjunctival redness and chemosis were 0.78, 0.66, 1.6 and 1 respectively. Since, in 2 out of 3 tested animals lesions of the iris with a score equal to 1 were induced, octanoic acid has to be considered as eye irritant at a concentration of 70%.
Based on the fact, that corrosion of the skin was found, octanoic acid has to be regarded as serious eye damaging according to the Guidance on CLP criteria, although the available studies rather indicate an eye irritation potential.
The available data on skin irritation/corrosion of octanoic acid meet the criteria for classfication as Skin Corr. 1C, H314 according to Regulation (EC) 1272/2008.
Data (1981a) revealed, that at and below a concentration of 70% no irrating properties are present. However, RAC does not support a specific concentration limit of 70% for skin corrosion, as the available data do not allow for their determination (RAC Opinion for octanoic acid, June 2013).
Based on the fact, that corrosion of the skin was found, octanoic acid has to be regarded as serious eye damaging according to the Guidance on CLP criteria.
Harmonised classification for octanoic acid (7th ATP; Index: 607-708-00-4): Skin Corr. 1C, H314
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