Zinc 3,5,5-trimethylhexanoate

Endpoint summary

Description of key information

No skin sensitisation study with zinc bis(3,5,5-trimethylhexanoate) is available, thus the skin sensitisation potential will be addressed with existing data on the individual moieties zinc and 3,5,5-trimethylhexanoic acid. According to the RAAF, neodecanoic acid will be considered in place of 3,5,5-trimethylhexanoic acid.

Zinc bis(3,5,5-trimethylhexanoate) is not expected to show signs of dermal sensitisation, since the two moieties zinc and 3,5,5-trimethylhexanoic acid, as represented by neodecanoic acid, have not shown any skin sensitisation potential in experimental testing.

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

No skin sensitisation study with zinc bis(3,5,5-trimethylhexanoate) is available, thus the skin sensitisation potential will be addressed with existing data on the individual moieties zinc and 3,5,5-trimethylhexanoic acid. According to the RAAF, neodecanoic acid will be considered in place of 3,5,5-trimethylhexanoic acid.

 

Zinc

The skin sensitising potential of zinc oxide (purity 99.69%) was investigated in female Dunkin Hartley guinea pigs in two well-performed maximisation tests, conducted according to Directive 96/54/EC B.6 and OECD guideline 406. Based on the results of a preliminary study, in the main studies experimental animals (10 in each test) were intradermally injected with a 20% concentration and epidermally exposed to a 50% concentration (i. e. the highest practically feasible concentration). Control animals (5 in each test) were similarly treated, but with vehicle (water) alone. Approximately 24 hours before the epidermal induction exposure all animals were treated with 10% SDS. Two weeks after the epidermal application all animals were challenged with a 50% test substance concentration and the vehicle. In the first study, in response to the 50% test substance concentration skin reactions of grade 1 were observed in 4/10 experimental animals 24 hours after the challenge (40% sensitisation rate), while no skin reactions were evident in the controls. In contrast, in the second study no skin reactions were evident in the experimental animals (0% sensitisation rate), while a skin reaction grade 1 was seen in one control animal. The skin reaction observed in one control animal is probably a sign of non specific irritation (Van Huygevoort, 1999b1, 1999b2).

In a third well-performed maximisation test, conducted according to the same guidelines and with the same experimental design, another analytical grade zinc oxide was tested (Zincweiß Pharma A; purity 99.9%). The only difference with the studies described above was the intradermal induction concentration, which was 2% as for Zincweiß Pharma A this was considered the highest concentration that could reproducibly be injected. In this test no skin reactions were evident in both experimental and control animals, hence a 0% sensitisation rate for Zincweiß Pharma A. White staining of the treated skin by the test substance was observed in some animals 24 and 48 hours after challenge (Van Huygevoort, 1999a).

Human data:

In a human patch test performed with 100 selected leg-ulcer patients, 11/100 patients gave an allergic reaction with zinc ointment (60% ZnO and 40% sesame oil). However, 14/81 patients gave a positive response when treated with sesame oil alone. This study does not give any indication for a skin sensitizing potential of zinc oxide in humans (Malten and Kuiper, 1974).

The effect of zinc oxide on contact allergy to colophony was investigated. With 14 patients with earlier history of moderate patch test reactions to colophony (a patch test) with 10% ZnO (2.3 mg Zinc/cm²) with and without colophony was performed. No positive response was observed in the 14 patients when only a 10% solution of zinc oxide was used. The addition of zinc oxide to colophony decreased the allergic reaction induced by colophony (Söderberg et al., 1990). All available data suggests this compound does not have skin sensitisation potential.

 

Neodecanoic acid

 Neodecanoic acid has been examined for skin sensitization potential in the guinea pig maximization procedure of Magnusson and Kligman. Groups of ten male and ten female guinea pigs were used for the test and a further five males and five females as controls. Induction was accomplished in two stages. 

 1) Intradermal injection: Two rows of three injections were made, one on each side of the midline in the shorn skin of the shoulder region. 2) Topical application: One week after the intradermal injections, the same area was clipped free from hair. A 4x4 cm patch of filter paper was soaked in a solution of the test material and placed over the injection sites and covered with an occlusive dressing. The dressing was left in place for 48 hours. The challenge procedure was carried out two weeks after topical induction. Challenge was accomplished by topical application of the test material to the flank of animals via an occluded patch. The challenge lasted 24 hours. Immediately after the challenge, and then again at 24 and 48 hours later, each animal was examined for signs of skin sensitization. At no point was there any evidence of skin sensitization produced by neodecanoic acid.   

 

Zinc bis(3,5,5-trimethylhexanoate)

Zinc bis(3,5,5-trimethylhexanoate) is not expected to show signs of dermal sensitisation, since the two moieties zinc and 3,5,5-trimethylhexanoic acid, as represented by neodecanoic acid, have not shown any skin sensitisation potential in experimental testing. Thus, zinc bis(3,5,5-trimethylhexanoate) is not to be classified according to regulation (EC) 1272/2008 as skin sensitising. Further testing is not required. For further information on the toxicity of the individual assessment entities, please refer to the relevant sections in the IUCLID and CSR.

Justification for classification or non-classification

Zincbis(3,5,5-trimethylhexanoate)is not expected to show signs of dermal sensitisation, since the two moieties zinc and 3,5,5-trimethylhexanoic acid, as represented by neodecanoic acid, have not shown any skin sensitisation potential in experimental testing. Thus, zinc bis(3,5,5-trimethylhexanoate)is not to be classified according to regulation (EC) 1272/2008 as skin sensitising.