Zinc oxide

Endpoint summary

Description of key information

Skin irritation/corrosion:

Data from an in vivo skin irritation study performed on New Zealand white rabbits with 20% w/v test item ZnO (Landsdown, 1991), indicate that the test item is not irritant to rabbit skin.

Eye irritation:

Data from an in vivo eye irritation study performed in 1999 on New Zealand white rabbits with zinc oxide (Van Huygevoort et al, 1999) according to OECD No. 405 guideline and EU Method B.5 (Directive 92/69/EEC), indicate that the test item is not irritant.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Endpoint:

skin irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

Macroscopic skin reactions, skin histological changes and epidermal keratin binding of test material were observed in New Zealand White rabbits after 5 d application of test material to skin using both open and occlusive patch methods.

GLP compliance:

not specified

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Sex: Male
- Source: Charing Cross and Westminster Medical School, London, UK
- Weight at study initiation: 2.5-4.0 kg
- Housing: Housed singly
- Diet: R14 pellets (Biosure) (zinc content 74 mg/kg, w/w)
- Water: Tap water
- Acclimation: Acclimatized to conventional restraining boxes before open patch test


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18±2
- Humidity (%): 45
- Photoperiod (h dark/h light): 12/12

Type of coverage:

other: Both open and occlusive in two different tests

Preparation of test site:

other: Clipped

Vehicle:

other: 0.1 % Tween 80

Controls:

yes, concurrent vehicle

Amount / concentration applied:

TEST SOLUTION
- Amount(s) applied (volume): 0.5 mL
- Concentration (if solution): 20 % (w/v) zinc oxide suspension in 0.1 % Tween 80
- pH: 7.4

Duration of treatment / exposure:

5 d

Observation period:

Open patch test: Observed during and after 5 d exposure period
Occlusive patch test: On Day 3 and Day 5

Number of animals:

Four animals each for control and test groups in both open and occlusive patch test

Details on study design:

Open patch test: Eight test sites (5 cm2) were designated, four on each side of the mid-dorsal line. Test suspension or vehicle was applied daily for 5 successive days. The animals were restrained for 30 min to allow test sites to dry. Skin sites were observed during and after 5 d exposure period. Rabbits were killed 24 h after the fifth daily treatment.

Occlusive patch test: Animals were prepared similar to open patch test. Test suspension or vehicle was applied to the skin on a sterile gauze pad that was secured by a hypoallergenic adhesive tape. The trunks of these animals were wrapped in rubberized fabric and impermeable dressing for 3 d. At this stage, dressings were removed and skin sites were evaluated for irritancy. Two rabbits were killed at this stage. The remaining animals were redressed with freshly impregnated gauze pads and then re-examined and killed after a further 2 d.

In both tests, representative samples of each test and control skin sites of killed animals were preserved in 10 % phosphate buffered formalin for histology. Thin sections cut along the anterior-posterior axis were stained with haematoxylin and eosin, or with morin dye, which fluoresces blue-green in the presence of zinc ions and ultraviolet light (to demonstrate zinc binding to epidermal keratin histologically).

SCORING SYSTEM: Not reported

Irritation parameter:

erythema score

Basis:

animal #1

Time point:

other: 5 d

Reversibility:

not specified

Remarks on result:

no indication of irritation

Irritation parameter:

erythema score

Basis:

animal #2

Time point:

other: 5 d

Reversibility:

not specified

Remarks on result:

no indication of irritation

Irritation parameter:

erythema score

Basis:

animal #3

Time point:

other: 5 d

Reversibility:

not specified

Remarks on result:

no indication of irritation

Irritation parameter:

erythema score

Basis:

animal #4

Time point:

other: 5 d

Reversibility:

not specified

Remarks on result:

no indication of irritation

Irritation parameter:

erythema score

Time point:

24 h

Remarks on result:

not measured/tested

Irritation parameter:

erythema score

Time point:

48 h

Remarks on result:

not measured/tested

Irritation parameter:

erythema score

Time point:

72 h

Remarks on result:

not measured/tested

Irritation parameter:

edema score

Time point:

24/48/72 h

Remarks on result:

not measured/tested

Irritant / corrosive response data:

No obvious reactions were observed in both control and treatment groups in any of the performed tests after 5 d exposure.

Other effects:

Histological changes: No evidence of damage was observed.

Morin fluorescence for zinc on skin: No obvious reaction was observed.

None

Interpretation of results:

not irritating

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

Based on these results, 20 % w/v zinc oxide was found to be non-irritating to rabbit skin.

Executive summary:

A study was conducted to evaluate the skin irritation potential of zinc oxide in New Zealand White rabbits by both open and occlusive patch methods.

In open patch test, 0.5 mL of 20 % w/v zinc oxide suspension in 0.1 % Tween 80 or vehicle was applied to clipped sites (5 cm²) of groups of four animals for 5 d. Skin sites were observed during and after 5 d exposure period. Animals were killed 24 h after the fifth daily treatment.

In occlusive patch test, groups of four animals were treated similarly to open patch test, but the test suspension or vehicle was applied to the skin using occlusive dressing for 3 d. After 3 d, dressings were removed and skin sites evaluated for irritancy. Two rabbits were killed at this stage. The remaining animals were redressed with freshly impregnated gauzes and then re-examined and killed after a further 2 d.

In both tests, representative samples of each test and control skin site of killed animals were analysed histologically and stained with morin dye to study epidermal keratin binding of zinc.

No obvious reactions were observed in both control and treatment groups in any of the performed tests after 5 d exposure. No evidence of damage was observed upon histological examination. No morin fluorescence was observed in skin sections.

Based on these results, 20 % w/v zinc oxide was found to be non-irritating to rabbit skin.

 

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Link to relevant study records

Reference

Endpoint:

eye irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method B.5 (Acute Toxicity: Eye Irritation / Corrosion)

Qualifier:

according to guideline

Guideline:

OECD Guideline 405 (Acute Eye Irritation / Corrosion)

GLP compliance:

yes

Species:

rabbit

Strain:

New Zealand White

Details on test animals or tissues and environmental conditions:

see reference

Vehicle:

unchanged (no vehicle)

Controls:

yes, concurrent no treatment

Amount / concentration applied:

64 mg ZnO (volume of 0.1 mL)

Duration of treatment / exposure:

24 hours

Observation period (in vivo):

1, 24, 48 and 72 hours after exposure

Number of animals or in vitro replicates:

3 males

Details on study design:

see reference

Irritation parameter:

conjunctivae score

Basis:

mean

Time point:

24/48/72 h

Score:

>= 0.7 - <= 1

Max. score:

3

Reversibility:

fully reversible

Remarks:

in 72h

Remarks on result:

no indication of irritation

Irritation parameter:

cornea opacity score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

4

Remarks on result:

no indication of irritation

Irritation parameter:

iris score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

2

Remarks on result:

no indication of irritation

Irritation parameter:

chemosis score

Basis:

mean

Time point:

24/48/72 h

Score:

0

Max. score:

4

Remarks on result:

no indication of irritation

Irritant / corrosive response data:

No symptoms of systemic toxicity were observed and no mortality occurred. Slight iridial irritation (grade 1) was observed in one animal, at 1 hour only. Slight irritation of the conjuctivae (grade 1-2) was seen as redness (mean scores over 24-72 hours 0.7, 1 and 1), which had completely resolved at 72 hours in all animals. Chemosis (grade 2) and discharge (grade 1) were also observed in all animals, but at 1 hour only. No corneal opacity or epithelial damage was observed in any of the animals

Other effects:

none

Interpretation of results:

GHS criteria not met

Conclusions:

ZnO not irritating in an vivo rabbit study.

Executive summary:

In an eye irritation/corrosion well-performed study according to Directive 92/69/EEC B.5 and OECD guideline 405, three male New Zealand White rabbits were treated by instillation of approximately 64 mg of zinc oxide (a volume of about 0.1 ml) into the conjuctival sac of one eye. The other eye remained untreated and served as control. After 24 hours, both eyes of two animals were rinsed with water. The eyes were examined at 1, 24, 48 and 72 hours after instillation. No symptoms of systemic toxicity were observed and no mortality occurred. Slight iridial irritation (grade 1) was observed in one animal, at 1 hour only. Slight irritation of the conjuctivae (grade 1-2) was seen as redness (mean scores over 24-72 hours 0.7, 1 and 1), which had completely resolved at 72 hours in all animals. Chemosis (grade 2) and discharge (grade 1) were also observed in all animals, but at 1 hour only. No corneal opacity or epithelial damage was observed in any of the animals.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Skin irritation/corrosion:

An in vivo skin irritation study from 1991 was performed on New Zealand white rabbits with 20% w/v test item Zinc Oxide (Lansdown, 1991). Macroscopic skin reactions, skin histological changes and epidermal keratin binding of test material were evaluated after skin exposure to the test material during 5 days, using both open and occlusive patch methods.

There were no obvious reactions in both control and treatment groups in any of the performed tests after 5 days. No evidence of damage was observed upon histological exmaination. No morin fluorescence was observed in skin sections. Therefore under the condition of this assay the test item was considered as being non-irritant to rabbit skin.

Eye irritation:

An in vivo eye irritation study was performed in 1999 on New Zealand white rabbits with zinc oxide (Van Huygevoort et al, 1999). The irritation effects of the test item were evaluated according to OECD No. 405 guideline and EU Method B.5 (Directive 92/69/EEC). Three rabbits were treated by instillation of 64mg ZnO in one eye for a duration of 24hours, the other (untreated eye) was used as control.

No symptoms of systemic toxicity were observed, no mortality occured, no corneal opacity or epithelial damage were observed. Only the following were present: slight iridial irritation at 1 hour  in one animal, slight irritation of the conjuctivae (redness) in all animals which completely resolved at 72 hours, grade 2 chemosis and grade 1 discharge at 1 hour in all animals.

Under the condition of this test, the test item was considered as being non-irritant to the rabbit eye.

Justification for classification or non-classification

Skin irritation:

Based upon the in vivo skin rabbit irritation data, zinc oxide is not irritating to the skin and therefore does not require classification

 

Eye irritation:

 

Based upon the in vivo eye rabbit irritation data, zinc oxide is not irritating to the eye and therefore does not require classification