N,N”-hexane-1,6-diylbis(N’-alkylaryl)urea

Endpoint summary

Description of key information

skin irritation (OECD 404, OECD 439): not irritating
eye irritation (OECD 405; OECD 437): not irritating

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:

no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Skin

The skin irritation potential of the test substance was determined by an in vitro skin irritation test using a human skin model and by a primary skin irritation/corrosion study in the rabbit.

The skin irritation potential of the test substance was determined by an in vitro skin irritation test using a human skin model according to OECD Guideline 439 and in compliance with GLP (Andres, 2014). In average, 24.9 mg test substance was applied topically to moistened (DPBS buffer) human skin tissues (EpiDermTM) with a tissue size of 0.63 cm² for 60 min. After a 42 ± 2 h post-incubation period, the cytotoxic (irritancy) effect was assessed. Cell viability is measured by dehydrogenase conversion of MTT, present in cell mitochondria, into a blue formazan salt, that is quantitatively measured after extraction from tissues. DPBS buffer was used as negative control, 5% SDS solution was used as positive control. The relative mean tissue viability obtained after 60 min treatment with the test substance compared to the negative control tissues was 101.8%. Since the mean relative tissue viability for the test substance was above 50% after 60 min treatment the test substance is considered to be non-irritant. The optical density of the negative control was well within the required acceptability criterion of 0.8 ≤ mean OD ≤ 2.8. The positive control 5% sodium dodecyl sulphate solution revealed a mean cell viability of 2.2% (required ≤ 20%) after 60 min exposure and thus ensuring the validity of the test system. Variation within replicates was acceptable. Based on the results, the test substance was not irritating to the skin under the conditions of the test.

 

In a primary skin/corrosion study according to OECD Guideline 404 and in compliance with GLP 0.5 g test substance moistened with 50% (v/v) ethanol-water was applied sequentially to the clipped skin of 3 male New Zealand White rabbits under semi-occlusive conditions for 4 h (Latour, 2015). Scoring of skin reactions (erythema and edema) was performed 1, 24, 48 and 72 h after removal of the patch. No skin irritation was caused by 4 hours exposure to the test substance and no staining of the treated skin by the test substance was observed. Furthermore, no test substance remnants were seen and no signs of systemic toxicity were observed in the animals during the test period and no mortality occurred. Based on the results, the test substance was not irritating to the skin under the conditions of the test.

 

In conclusion, the test substance is non-irritant in the in vitro skin irritation test and in the in vivo primary skin/corrosion study in rabbits under the experimental conditions used.

 

Eye

The eye irritation potential of the test substance was determined by a bovine corneal opacity and permeability test (BCOP test) and by an acute eye irritation study in the rabbit.

The eye irritation potential of the test substance was determined in a bovine corneal opacity and permeability test (BCOP test) according to OECD Guideline 437 and in compliance with GLP (Andres, 2014). The solid test substance was applied directly to the epithelial surface of three cattle corneas for 4 h ± 5 min at 32 ± 1 °C. After exposure the corneas were washed and opacity values were measured. In addition the permeability of the corneas was measured with a photometer after incubation of the corneas with sodium fluorescein solution for 90 min. The results of the opacity and permeability measurement of the test substance were used to calculate an in vitro irritation score (IVIS) of - 0.585. The negative control showed no irritation effects and no serious eye damage, mean IVIS was 1.333. The mean in vitro irritation score of the positive control (20% (w/v) imidazole) was 118.485. All three values for negative and two values for positive controls were within the range of historical data of the test facility. Therefore, the test system was acceptable. The value of the positive control, which lay outside of the historical data, can be seen as uncritical, because the value showed a clear positive result. Based on the results, the test substance was not irritating to the eye under the conditions of the test.

In an acute eye irritation study according to OECD Guideline 405 and in compliance with GLP samples of 21.4 mg test substance (corresponds to a volume of approx. 0.1 mL) were instilled into one eye of each of 3 male New Zealand White rabbits (Latour, 2015). Eye reactions were scored 1, 24, 48 and 72 h after instillation. Instillation of the test substance resulted in irritation of the conjunctivae, which consisted of redness, chemosis and discharge. The irritation had completely resolved within 24 hours in two animals and within 48 hours in the other animal. No iridial irritation or corneal opacity were observed. Remnants of the test substance were present on the outside of the eyelids of all animals on Day 1. The overall mean irritation score over 24, 48 and 72 h for chemosis, iris and corneal effects was 0. The irritation score over 24, 48 and 72 h for conjunctival redness was 0 in two animals and 0.3 in one animal. No signs of systemic toxicity were observed in the animals during the test period and no mortality occurred. Based on the results, the test substance was not irritating to the eyes under the conditions of the test.

 

In conclusion, the test substance is non-irritant in the in vitro eye irritation test and in the in vivo acute eye irritation study in rabbits under the experimental conditions used.

Justification for selection of skin irritation / corrosion endpoint:
No study was selected since the in vitro and the in vivo guideline study were adequate and reliable.

Justification for selection of eye irritation endpoint:
No study was selected since the in vitro and the in vivo guideline study were adequate and reliable.

Justification for classification or non-classification

The available data on skin and eye irritation of the test substance do not meet the criteria for classification according to Regulation (EC) 1272/2008 or Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.