4-hydroxy-2,2,6,6-tetramethylpiperidinoxyl

Endpoint summary

Description of key information

The skin irritation/corrosion of 4-Hydroxy-TEMPO was tested in a standard OECD 404 guideline study. Classification: not irritating. 
The eye irritation of 4-Hydroxy-TEMPO was tested in a standard OECD 405 guideline study. Classification: H318, Causes serious eye damage.

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Skin irritation

In a GLP-compliant OECD guideline 404 study (95-0256-DGT), three male Russian White rabbits were treated with 0.5 g 4-Hydroxy-TEMPO moistened with 0.5 cm³ water using semiocclusive conditions for 4 hours. An application site of approximately 6 cm² was covered with the test substance. The animals were observed for 72 hours and skin changes were recorded for every animal after 30 to 60 minutes, 24, 48 and 72 hours. The application of the test substance to the skin caused a slight edema in one rabbit and a slight erythema in all three rabbits. Signs of edema and erythema fully reversed within 72 hours at the latest. No signs of toxicity were observed. The individual average scores (24 to 72 h) for irritation did not warrant a classification, thus the test substance has to be classified as not irritating according to EU criteria. The study is classified as key study and the results are acceptable.

Eye irritation

In a GLP-compliant OECD guideline 405 study (95-0254-DGT), the right eye of three male Russian White rabbits was exposed to 0.1 g 4-Hydroxy-TEMPO, placed as dry substance into the conjunctival sac of the eyelid. Animals were observed after 1, 24, 48 and 72 hour(s) of treatment and 6, 8, 10, 13, 16, 21 and 24 days afterwards. The eyes were washed out with physiological saline solution after 24 hours. Overall, the treatment caused opacity and conjunctivae/chemosis of the eye mucous membranes as well as exsudation and detachment of upper layers of mucosa at 48 h. In 2 of 3 animals the effects were slowly reversible after 13 to 21 days. In one animal hyperaemia, swelling of the conjunctivae and corneal opacity persisted up to day 21. Due to the individual average scores (24 to 72 h) of conjunctivae, chemosis, opacity and iritis the test substance was graded as irritant under the conditions of this study. This GLP-compliant study satisfies the requirements of OECD test guideline 405 and is classified as acceptable (key study).

Justification for selection of skin irritation / corrosion endpoint:
Adequate assay to address endpoint

Justification for selection of eye irritation endpoint:
Adequate assay to address endpoint

Effects on eye irritation: highly irritating

Justification for classification or non-classification

Based on the results for in vivo skin irritation, 4-Hydroxy-TEMPO should be classified as not irritating to skin according to the criteria of EU Directive 67/548/EEC and according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No 1272/2008.

Based on the results of the in vivo eye irritation study, the test substance should be classified as Xi, R41 (Irritant, Risk of serious damage to eyes) according to the criteria of EU Directive 67/548/EEC and as Cat. 1, H318 (causes serious eye damage) according to EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No 1272/2008.