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Diss Factsheets

Administrative data

Description of key information

1. Information on zirconium dioxide
Skin irritation / corrosion:
Zirconium dioxide was observed not to be irritating to the skin of New Zealand White rabbit in an in vivo skin irritation study performed according to OECD guideline 404 (BIBRA, 1986).
Eye irritation:
Yttrium zirconium oxide was observed to be slightly irritating to New Zealand rabbit eyes in an in vivo eye irritation study performed according to a method equivalent to OECD Guideline 405 (Chemical Evaluation and Research Institute, 2000), however, the substance does not need to be classified (DSD, CLP) for eye irritation.
2. Information on magnesium oxide
For magnesium oxide, results of studies performed with magnesium hydroxide were included in the weight of evidence approach. Since magnesium oxide is transformed to magnesium hydroxide when in contact with moisture, these results are considered representative for magnesium oxide too.
Skin irritation / corrosion:
Based on the results of an in vitro skin corrosion test performed according to OECD guideline 431 (Buskens, 2010a) and an in vitro skin irritation test performed according to OECD guideline 439 (Buskens, 2010b), magnesium hydroxide should not be classified as irritating to skin. Consequently, magnesium oxide can also be considered as not irritating to skin.
Eye irritation:
Based on the results of a BCOP study (OECD 437; Verspeek-Rip, 2010a) and in vivo eye irritation study in New Zealand White rabbits (OECD 405; van Otterdijk, 2010b), magnesium hydroxide should not be classified as eye irritant. Consequently, magnesium oxide can also be considered as not irritating to eyes.
3. Conclusion on magnesium zirconium oxide
No reliable studies are available for magnesium zirconium oxide itself. Based on the available data for the individual substances magnesium (hydr)oxide and zirconium dioxide it is concluded that the substance does not need to be classified for skin or eye irritation.

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Referenceopen allclose all

Endpoint:
skin corrosion: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2010-03-02 to 2010-03-05
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 431 (In Vitro Skin Corrosion: Human Skin Model Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: EC Guideline 440 (Part B: Methods for determination of toxicity and other health effects, Guideline B.40 BIS "In vitro corrosion: Human skin model test"
Deviations:
no
GLP compliance:
yes
Remarks:
Self-Certified
Test system:
human skin model
Source species:
human
Cell type:
non-transformed keratinocytes
Vehicle:
water
Details on test system:
The potential of magnesium hydroxide to induce skin corrosion was tested using a human three-dimensional epidermal model.
This model consisted of normal, human-derived epidermal keratinocytes which were cultured to form a multilayered, highly differentiated model of the human epidermis. It consisted of organised basal, spinous and granular layers, and a multilayered stratum corneum containing intercellular lamellar lipid layers arranged in patterns analogous to those found in vivo.

Magnesium hydroxide was assessed for its ability to directly reduce MTT before the study was started to ensure that this would not interfere with the results obtained. Approximately 100 mg of magnesium hydroxide was added to a 24-well plate filled with 1 mL MTT medium. The mixture was incubated for 1 hr at room temperature in the dark. As a negative control, sterile Milli-Q water was tested concurrently.

On the day of receipt, skin tissues were stored on agarose at 4°C. The following day, at least 1 hour prior to starting the assay, the tissues were transferred to 6-well plates containing 0.9 mL DMEM per well. The level of DMEM medium just reached the underside of the tissue. The plates were incubated for 1 hr 50 min at 37°C with 5% CO2. The medium was replaced with fresh DMEM medium and the tissue was moistened with 25 µL of Milli-Q water just prior to application of the test substance. The test was performed with a total of 4 tissues per test substance together with a negative control and positive control. 25 mg of Mg(OH)2 was applied directly on top of the moistened skin tissue. Two tissues were used for a 3-minute exposure to Mg(OH)2 and two for a 1-hour exposure. The negative and positive controls were treated with 50 µL Milli-Q water and 50 µL 8N KOH, respectively.

After the exposure period, the tissues were washed with PBS to remove residual test substance. Rinsed tissues were kept in 24-well plates on 300 µL DMEM until 6 tissues were dosed and rinsed.

To measure cell viability, the DMEM was replaced with 300 µL MTT-medium and tissues were incubated for 3 hours at 37°C in 5% CO2. After incubation the tissues were washed with PBS and formazan was extracted with 2 mL isopropanol over night at room temperature. The amount of extracted formazan was determined spectrophotometrically at 540 nm in triplicate. Cell viability was calculated for each tissue as a percentage of the mean of the negative control tissues. Skin corrosion potential of the test substance was classified according to remaining cell viability following exposure of the test substance with either of the two exposure times.
Control samples:
yes, concurrent negative control
yes, concurrent positive control
Amount/concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 25 mg of magnesium hydroxide was applied directly on top of skin tissue which was moistened with 25 µL of Milli-Q water to ensure close contact to the tissue.
Duration of treatment / exposure:
3 minutes and 1 hour
Duration of post-treatment incubation (if applicable):
To measure cell viability, the DMEM was replaced with 300 µL MTT-medium and tissues were incubated for 3 hours at 37°C in 5% CO2.
Number of replicates:
4 tissues per test substance, 2 for 3 min exposure and 2 for 1 h exposure
Irritation / corrosion parameter:
other: % viability of skin cells
Value:
88
Remarks on result:
other: Basis: mean. Time point: 3 minutes. Max. score: 100.0.
Irritation / corrosion parameter:
other: % viability of skin cells
Value:
95
Remarks on result:
other: Basis: mean. Time point: 1 hour. Max. score: 100.0.
Irritant / corrosive response data:
See field "Any other information on results incl. tables"

Magnesium hydroxide was checked for possible direct MTT reduction by adding the test substance to MTT medium. Because no colour change was observed it was concluded that magnesium hydroxide did not interact with MTT.

The mean absorption at 540 nm measured after treatment with magnesium hydroxide and controls are presented in Table 1. Table 2 shows the mean tissue viability obtained after 3 minute and 1 hour treatments with magnesium hydroxide compared to the negative control tissues. Skin corrosion is expressed as the remaining cell viability after exposure to the test substance.

A test substance is considered corrosive in the skin corrosion test if:

1. The relative mean tissue viability obtained after 3 minutes of treatment compared to the negative control tissues is decreased below 50%.

2. The relative tissue viability after 1 hour of treatment is decreased below 15%.

 

A test substance is considered to be non-corrosive if: 

1. The relative mean tissue viability obtained after 3 minutes of treatment compared to the negative control tissues is above 50%.

2. The relative tissue viability after 1 hour of treatment is not decreased below 15%. The relative mean tissue viability obtained after the 3 minute and 1 hour treatments with magnesium hydroxide compared to the negative control tissues were 88% and 95%, respectively. The absolute mean OD540 of the negative control tissues was within the historical control range. The mean relative tissue viability following 3 minutes and 1 hour of exposure to the positive control were 9%. Therefore, it was concluded that the test system was suitable for this analysis. Table 1: Mean absorption in the in vitro skin corrosion test with magnesium hydroxide (OD540)

 

3 minute application

1 hour application

 

A

B

Mean ± SD

A

B

Mean ± SD

Negative control

1.683

1.699

1.691 ± 0.011

1.707

1.710

1.708 ± 0.002

Magnesium hydroxide

1.586

1.393

1.490 ± 0.137

1.664

1.578

1.621 ± 0.061

Positive control

0.150

0.143

0.147 ± 0.005

0.148

0.145

0.147 ± 0.002

  

Table 2: Mean tissue viability

 

 

3 minute application viability (% of control)

1 hour application viability (% of control)

Negative control

100

100

Magnesium hydroxide

88

95

Positive control

9

9

Interpretation of results:
GHS criteria not met
Conclusions:
Based on the results of this study, it is concluded that magnesium hydroxide is not corrosive in the in vitro skin corrosion test.
Executive summary:

The potential of magnesium hydroxide to induce skin corrosion was tested using a human three-dimensional epidermal model. The possible corrosive potential of magnesium hydroxide was tested using topical application for either 3 minutes or 1 hour. Twenty five mg of magnesium hydroxide was added directly on top of the skin tissue which was moistened with water. Water and potassium hydroxide were used as the negative and positive control substances, respectively.

The positive control had a mean relative tissue viability of 9% after 3 minutes exposure, and the absolute mean optical density of the negative control tissues was within the historical control range, indicating the acceptability of the assay.

The mean relative tissue viabilities for magnesium hydroxide after 3 minute and 1 hour treatments were 88% and 95%, respectively. Because the mean relative tissue viability for magnesium hydroxide was not below 50% after the 3 minute treatment or 15% after the 1 hour treatment, it was concluded that magnesium hydroxide is not corrosive under the conditions of this test.

Endpoint:
skin irritation: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2010-04-27 to 2010-05-03
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method B.46 (In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test)
Deviations:
no
GLP compliance:
yes
Remarks:
Self-Certified
Test system:
human skin model
Source species:
human
Cell type:
non-transformed keratinocytes
Vehicle:
water
Details on test system:
The potential of magnesium hydroxide to induce skin corrosion was tested using a human three-dimensional epidermal model (EPISKIN). This model consisted of adult human-derived epidermal keratinocytes which were seeded on a dermal substitute consisting of a collagen type I matrix coated with type IV collagen. The keratinocytes were cultured for 13 days, which results in a highly differentiated and stratified epidermis model comprising the main basal, supra basal, spinous and granular layers of a functional stratum corneum.

Magnesium hydroxide was assessed for its ability to directly reduce MTT before the study was started to ensure that this would not interfere with the results obtained. Approximately 100 mg of magnesium hydroxide was added to a 24-well plate filled with 1 mL MTT medium. The mixture was incubated for 1 hr at room temperature in the dark. As a negative control, sterile Milli-Q water was tested concurrently.

On the day of receipt, skin tissues were transferred to 12-well plates and preincubated with pre-warmed Maintenance Medium for 24 hours at 37°C. The level of medium just reached the underside of the tissue. The test was performed with a total of 3 tissues per test substance together with a negative control and positive control. Three tissues were treated with a negative control (10 µL PBS) and 3 tissues with a positive control (10 µL of 5% SDS). The positive control was re-spread after 7 minutes contact time. After the exposure period of 15 minutes at room temperature, the tissues were washed with PBS to remove residual test substance. Rinsed tissues were kept in 12-well plates on 2 mL pre-warmed Maintenance Medium until all tissues were dosed and rinsed. Subsequently, the skin tissues were incubated for 42 hours at 37°C.

To measure cell viability, cell culture inserts were dried carefully to remove excess medium and were transferred into a 12-well plate prefilled with 2 mL MTT medium (0.3 mg/mL). The tissues were incubated for 3 hours at 37°C in 5% CO2. After incubation the tissues were placed on blotting paper to dry. Total biopsy was made using a biopsy punch. The epidermis was separated from the collagen matrix and both parts were placed in prelabelled microtubes and extracted with 500 µL of isopropanol. The amount of extracted formazan was determined spectrophotometrically at 570 nm in duplicate. Cell viability was calculated for each tissue as a percentage of the mean of the negative control tissues. Skin irritation potential of the test substance was classified according to remaining cell viability following exposure to the test substance.
Control samples:
yes, concurrent negative control
yes, concurrent positive control
Amount/concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 10 mg of magnesium hydroxide was applied directly on top of skin tissue which was moistened with 25 µL of Milli-Q water to ensure close contact to the tissue.
Duration of treatment / exposure:
15 minutes
Duration of post-treatment incubation (if applicable):
42 hours
Number of replicates:
3 tissues per test substance
Irritation / corrosion parameter:
other: % viability of skin cells
Value:
91
Remarks on result:
other: Basis: mean. Time point: 42 hours. Max. score: 100.0.
Irritant / corrosive response data:
See field "Any other information on results incl. tables"

Magnesium hydroxide was checked for possible direct MTT reduction by adding the test substance to MTT medium. Because no colour change was observed it was concluded that magnesium hydroxide did not interact with MTT.

The mean absorption at 570 nm measured after treatment with magnesium hydroxide and controls are presented in Table 1. Table 2 shows the mean tissue viability obtained after 15 minutes of treatment with magnesium hydroxide compared to the negative control tissues. Skin corrosion is expressed as the remaining cell viability after exposure to the test substance.

The in vitro skin irritation test is considered to be acceptable if it meets the following criteria:

 

  1. The absolute mean OD570 of the three tissues of the negative control should reasonably be within the laboratory historical control data range and the SD of the % viability should be ≤ 18
  2. The mean relative tissue viability of the positive control should be ≤ 40% relative to the negative control and the SD of the % viability should be ≤ 18
  3. The SD calculated from individual % tissue viabilities of the three identically treated replicates should be ≤ 18.

The relative mean tissue viability obtained after 15 minutes of treatment with magnesium hydroxide compared to the negative control tissues was 91%. As the mean relative tissue viability for magnesium hydroxide was above 50%, magnesium hydroxide is considered to be non-irritant. The absolute mean OD540 of the negative control tissues was within the historical control range. The mean relative tissue viability following 3 minutes and 1 hour of exposure to the positive control were 9%. Therefore, it was concluded that the test system was suitable for this analysis. Table 1: Mean absorption in the in vitro skin corrosion test with magnesium hydroxide (OD540)

 

 

A

B

C

Mean ± SD

Negative control

1.103

0.839

0.987

0.976 ± 0.133

Magnesium hydroxide

0.832

0.878

0.941

0.884 ± 0.055

Positive control

0.039

0.039

0.028

0.035 ± 0.006

  

Table 2: Mean tissue viability

 

 

Mean tissue viability

(% of control)

Negative control

100

Magnesium hydroxide

91

Positive control

4

Interpretation of results:
GHS criteria not met
Conclusions:
Based on the results of this study, it is concluded that magnesium hydroxide is non-irritant in the in vitro skin irritation test.
Executive summary:

The potential of magnesium hydroxide to induce skin irritation was tested using a human three-dimensional epidermal model. The possible skin irritation potential of magnesium hydroxide was tested using topical application for 15 minutes, followed by a 42 hour incubation period. Ten mg of magnesium hydroxide was added directly on top of the skin tissue which was moistened with water. Water and SDS were used as the negative and positive control substances, respectively.

The positive control had a mean relative tissue viability of 4% after 15 minutes exposure, and the absolute mean optical density of the negative control tissues was within the historical control range, indicating the acceptability of the assay.

The mean relative tissue viabilities for magnesium hydroxide after 15 minutes of treatment was 91%. Because the mean relative tissue viability for magnesium hydroxide was not below 50% after the 3 minute treatment or 15% after the 15 minute treatment, it was concluded that magnesium hydroxide is not a skin irritant under the conditions of this test.

Endpoint:
skin irritation: in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1986-03-04 to 1986-07-17
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented, scientifically sound GLP study that was based on the OECD Guideline 404 "Acute Dermal Irritation/Corrosion". The test substance was tested simultaneously on the same animals.
Qualifier:
according to guideline
Guideline:
OECD Guideline 404 (Acute Dermal Irritation / Corrosion)
Deviations:
yes
Remarks:
Substances were tested simultaneously on the same animals
GLP compliance:
yes
Species:
rabbit
Strain:
New Zealand White
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Regal Rabbits, Great Bookham, Surrey
- Housing: individually in metal grid-floored cages
- Diet: ad libitum, Grain Harvester's special rabbit diet 679
- Water: ad libitum tap water
- Acclimation period: 14 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-23
- Humidity (%): 43-74
Type of coverage:
occlusive
Preparation of test site:
shaved
Vehicle:
water
Controls:
not required
Amount / concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): spread on a patch previously moistened with 0.5 mL of water to ensure good contact with the skin
Duration of treatment / exposure:
4 hours
Observation period:
24, 48 and 72 hours
Number of animals:
4 male animals
Details on study design:
TEST SITE
- Area of exposure: dorsal
- Type of wrap if used: 2.5 cm square patches were applied to the skin on 6 cm square patches of polythene held in place by adhesive tape and elastic net bandages.

REMOVAL OF TEST SUBSTANCE
- Washing (if done): tap water
- Time after start of exposure: 4 hours

SCORING SYSTEM: Draize (1959), Indices of irritation were calculated for each animal by totalling the scores for oedema and erythema for each animal and dividing by two.
Irritation parameter:
overall irritation score
Basis:
mean
Time point:
24 h
Score:
ca. 0
Max. score:
8
Irritation parameter:
overall irritation score
Basis:
mean
Time point:
48 h
Score:
ca. 0
Max. score:
8
Irritation parameter:
overall irritation score
Basis:
mean
Time point:
72 h
Score:
ca. 0
Max. score:
8
Irritation parameter:
erythema score
Basis:
mean
Time point:
24/48/72 h
Score:
0
Max. score:
4
Irritation parameter:
edema score
Basis:
mean
Time point:
24/48/72 h
Score:
0
Max. score:
4
Irritant / corrosive response data:
No reaction to the test substances was reported in any of the test animals.
Interpretation of results:
GHS criteria not met
Conclusions:
The test substance was determined to be not irritating to the skin of rabbits.
Endpoint:
skin irritation / corrosion, other
Remarks:
in vitro and in vivo
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
Read across based on the study from BIBRA (1986) with zirconium dioxide and two studies from Buskens (2010a,b). The read across justification document is attached in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Irritation / corrosion parameter:
other: read across conclusion
Remarks on result:
other: Magnesium zirconium oxide was concluded not to be irritant to skin, in vitro.
Remarks:
Conclusion based on the read across studies from Buskens (2010a,b) performed with magnesium dihydroxide (in vitro) and the study of BIBRA (1996) performed with zirconium dioxide (in vivo).
Irritation parameter:
other: read across conclusion
Remarks on result:
other: Magnesium zirconium oxide was concluded not to be irritant to skin, in vivo.
Remarks:
Conclusion based on the read across study from BIBRA (1986) performed with zirconium dioxide (in vivo), and the read across studies from Buskens (2010a,b) performed with magnesium dihydroxide (in vitro).
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not irritating)

Eye irritation

Link to relevant study records

Referenceopen allclose all

Endpoint:
eye irritation: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2010-03-15 to 2010-03-16
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 437 (Bovine Corneal Opacity and Permeability Test Method for Identifying Ocular Corrosives and Severe Irritants)
Deviations:
no
GLP compliance:
yes
Remarks:
Self-Certified
Species:
other: Bovine
Strain:
not specified
Details on test animals or tissues and environmental conditions:
Bovine eyes from young cattle were obtained from the slaughterhouse, where the eyes were excised by a slaughterhouse employee as soon as possible after slaughter. The eyes were collected and transported in physiological saline in a suitable container and were used within 30 minutes.
Vehicle:
physiological saline
Controls:
yes, concurrent no treatment
Amount / concentration applied:
Unknown
Duration of treatment / exposure:
Topical treatment for 240 ± 10 minutes
Duration of post- treatment incubation (in vitro):
After incubation with the test substance, the solutions were removed, fresh cMEM was added and an opacity determination was performed without any further incubation.
Number of animals or in vitro replicates:
Three corneas were used in each treatment group.
Details on study design:
REMOVAL OF TEST SUBSTANCE
- Washing: After the incubation with the test substance, corneas were washed at least 3 times with cMEM prior to determination of opacity
- Time after start of exposure: 240 ± 10 minutes

OPACITY:
The opacitometer determined the difference in light transmission between each control and treated cornea and an air filled chamber. The numerical opacity value was displayed and recorded. The change in opacity for each individual cornea was calculated by subtracting the initial opacity reading from the post-treatment reading. The corrected opacity was calculated by subtracting the opacity of the negative control.

PERMEABILITY
Following the final opacity method, permeability of the cornea to Na-fluorescein was evaluated. The medium of both compartments (anterior compartment first) was removed. The posterior compartment was refilled with fresh cMEM. The anterior compartment was filled with 1 mL of Na-fluorescein solution. The corneas were completely covered and were incubated in a horizontal position for 90 ± 5 minutes at 37 ± 1 °C.

After the incubation period, the medium in the posterior compartment of each holder was removed and placed into a sampling tube labelled according to holder number. 360 µL of the medium from each sampling tube was transferred to a 96-well plate. The optical density at 490 nm of each sampling tube was measured in triplicate using a microplate reader.
Irritation parameter:
in vitro irritation score
Run / experiment:
240 min time point
Value:
5.1
Remarks on result:
other: maximum score 7.1
Irritation parameter:
cornea opacity score
Run / experiment:
240 min time point
Value:
5
Remarks on result:
other: maximum score 7.0
Irritation parameter:
other: permeability
Run / experiment:
240 min time point
Value:
0.006
Remarks on result:
other: maximum score 0.009
Other effects / acceptance of results:
See "Any other information on results incl. tables"

Table 1: Summary of opacity, permeability and in vitro scores

 

Treatment

 

Mean Opactiy

Mean Permeability 

 Mean In vitro Irritation Score1,2

 Negative control  0  0.000  0.0
 Positive control  80  2.490  117
 Magnesium hydroxide  5  0.006  5.1

1 Calculated using the negative control mean opacity and mean permeability values.

2 In vitro irritancy score (IVIS) = mean opacity + (15 x mean OD490value).

Table 2: Opacity score

 

Eye

Opacity before treatment

Opacity after treatment

Final opacity

Negative control corrected final opacity

Mean opacity

Negative control

1

0

0

0

0

0

2

0

1

1

1

3

0

0

0

0

Positive control

4

0

80

80

80

80

5

0

79

79

79

6

0

81

81

81

Magnesium hydroxide

10

0

6

6

6

5

11

0

3

3

3

12

0

7

7

7

  

Table 3: Permeability score (corrected)

  

Eye

Dilution factor

Corrected OD4901

Corrected OD4902

Corrected OD4903

Average

OD490

Final

OD490

Average

OD

Negative control

1

1

0.014

0.001

0.004

0.006

0.006

0.000

2

1

0.000

0.000

0.003

0.001

0.001

3

1

-0.001

-0.008

-0.009

-0.006

-0.006

Positive control

4

6

0.369

0.366

0.372

0.369

2.214

2.490

5

6

0.349

0.362

0.354

0.355

2.130

6

6

0.527

0.518

0.519

0.521

3.126

Magnesium hydroxide

10

1

0.008

0.008

0.011

0.009

0.009

0.006

11

1

0.008

0.002

0.000

0.003

0.003

12

1

0.006

0.004

0.005

0.005

0.005

  

Table 4: In vitro irritancy score

 

Eye

Negative control corrected final opacity

Negative control corrected final OD490

In vitro irritancy score

Negative control

1

0

0.006

0.1

2

0

0.001

1.0

3

0

-0.006

-0.1

Positive control

4

80

2.214

113.2

5

79

2.130

111.0

6

81

3.126

127.9

Magnesium hydroxide

10

6

0.009

6.1

11

3

0.003

3.0

12

7

0.005

7.1

In vitro irritancy score (IVIS) = mean opacity + (15 x mean OD490value).

Interpretation of results:
GHS criteria not met
Conclusions:
Since the mean in vitro irritancy score for magnesium hydroxide was below 55 after 240 minutes treatment, magnesium hydroxide is not classified as an irritant in the BCOP test.
Executive summary:

Screening for the eye irritancy potential of magnesium hydroxide using the BCOP test. The study procedures were based on OECD guidelines. Magnesium hydroxide did not induce ocular irritation through both endpoints, resulting in a mean in vitro irritancy score of 5.1 after 240 minutes of treatment. Since this score is below 55 after 240 minutes treatment, magnesium hydroxide is not classified as an irritant in the BCOP test.

Endpoint:
eye irritation: in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2010-04-06 to 2010-04-22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 405 (Acute Eye Irritation / Corrosion)
Qualifier:
according to guideline
Guideline:
EU Method B.5 (Acute Toxicity: Eye Irritation / Corrosion)
Qualifier:
according to guideline
Guideline:
EPA OPPTS 870.2400 (Acute Eye Irritation)
Qualifier:
according to guideline
Guideline:
other: JMAFF guidelines (2000); including the most recent partial revisions.
GLP compliance:
yes
Species:
rabbit
Strain:
New Zealand White
Details on test animals or tissues and environmental conditions:
TEST ANIMALS
- Source: Harlan, Belton, Leics, England
- Age at study initiation: Animals used within the study were at least 6 weeks old
- Weight at study initiation: Body weights were at least 1.0 kg
- Housing: Animals were individually housed in labelled cages with perforated floors and shelters.
- Diet: Pelleted diet for rabbits approximately 100 grams per day was provided at least three times a week.
- Water: Free access to tap water
- Acclimation period: Acclimatisation period was at least 5 days before start of treatment under laboratory conditions.
Results of analysis for diet, hay and water were assessed and did not reveal any findings that were considered to have affected the study integrity.
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.0±3.0°C
- Humidity (%): 40-70%
- Air changes (per hr): 15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12 hours artificial fluorescent light and 12 hours darkness per day.

IN-LIFE DATES: From: 06-04-2010 to: 2-04-2010

Test system:

Amount/ concentration applied:
Animals were treated by instillation of on average, 57.3 mg (range 57.0-57.5 mg) of the test substance (a volume of approximately 0.1 mL) in the conjunctival sac of one of the eyes.

Observation period:
Observations were made 1, 24, 48 and 72 hours after instillation.
Mortality/ Viability: Twice daily
Toxicity: At least once daily
Body weight: Day of treatment and after the final observation
Necropsy: No necropsy was performed according to protocol.
Irritation: The eyes of each animal were examined approximately 1, 24, 48 and 72 hours after instillation of the test substance. The irritation scores and a description of all other (local) effects were recorded.
Controls:
yes, concurrent no treatment
Amount / concentration applied:
57.3 mg in the conjunctival sac of one of the eyes (mean)
Duration of treatment / exposure:
Single treatment
Observation period (in vivo):
1, 24, 48 and 72 h
Number of animals or in vitro replicates:
3 males were used in the treatment.
Details on study design:
The study was performed in a stepwise manner and was started by treatment of a single rabbit. The other two animals were treated in a similar manner 2 weeks later, after considering the degree of eye irritation observed in the first animal.
Washing: Immediately after the 24-hour observation period, a solution of 2% fluorescein in water was instilled into both eyes of each animal to quantitatively determine corneal epithelial damage. The procedure was repeated to assess recovery. Any bright green stained area, indicating epithelial damage, was estimated as a percentage of the total corneal area.
Irritation parameter:
overall irritation score
Basis:
animal: number 1, 2 and 3.
Time point:
24 h
Score:
> 0 - <= 1
Reversibility:
other: The irritation of the conjunctivae consisted of redness, chemosis and discharge and completely resolved within 72 hours in all animals.
Irritation parameter:
cornea opacity score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritation parameter:
iris score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritation parameter:
chemosis score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritation parameter:
conjunctivae score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritant / corrosive response data:
Instillation of approximately 57 mg of magnesium hydroxide into one eye of each of three rabbits resulted in effects on the cornea, iris and conjunctivae. The corneal injury consisted of a slight dulling of the normal lusture and/or epithelial damage (maximum 10% of the corneal area) in two animals. The corneal injury had resolved within 24 or 48 hours. Iridial irritation grade 1 was observed in all animals and had resolved within 24 hours. The irritation of the conjunctivae consisted of redness, chemosis and discharge and completely resolved within 72 hours in all animals.

Coloration/ Remnants:
Remnants of the test substance were present in the eye of two animals on Day 1.

Toxicity/ Mortality:
No symptoms of systemic toxicity were observed in the animals during the test period and no mortality occurred.

Table 1:

Mean value eye irritation scores

 

 

Mean 24, 48 and 72 hours.

Animal

Corneal

opacity

Iris

Conjunctivae

 

Redness

Chemosis

328

0.0

0.0

1.0

0.0

377

0.0

0.0

1.0

0.3

379

0.0

0.0

1.0

0.3

 

 

Table 2:

Animal specifications

 

Animal

Sex

Age at start

(weeks)

Body weights( grams)

 

 

 

Prior to application

At termination

328

Male

10-12

2198

2256

377

Male

7-9

1516

1701

379

Male

7-9

1615

1739

 

Interpretation of results:
GHS criteria not met
Conclusions:
Based on these results magnesium hydroxide does not have to be classified and has no obligatory labelling requirement for eye irritation according to the:
- Globally Harmonised System of Classification and Labeling of Chemicals (GHS) of the United Nations
- Regulation (EC) No 1272/2008 on classification, labelling and packaging of substances and mixtures.
Endpoint:
eye irritation, other
Remarks:
in vitro and in vivo
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
Read across based on the study of the Chemical Evaluation and Research Institute (2000) with yttrium zirconium dioxide, a study from Verspeek-Rip (2010a) and a study from van Otterdijk (2010b). The read across justification document is attached in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Irritation parameter:
other: read across conclusion
Remarks on result:
other: Magnesium zirconium oxide was concluded not to be irritant to eyes, in vitro.
Remarks:
Conclusion based on the read across study from Verspeek-Rip (2010a) performed with magnesium hydroxide (in vitro) and the read across studies from van Otterdijk (2010b) with magnesium hydroxide and the Chemical Evaluation and Research Institute (2000) with yttrium zirconium oxide (in vivo).
Irritation parameter:
other: read across conclusion
Remarks on result:
other: Magnesium zirconium oxide was concluded not to be irritant to eyes, in vivo.
Remarks:
Conclusion based on the read across studies from the Chemical Evaluation and Research Institute (1986) performed with yttrium zirconium oxide and van Otterdijk (2010b) performed with magnesium hydroxide (in vivo) as well as the study from Verspeek-Rip (2010a) performed with magnesium hydroxide (in vitro).
Endpoint:
eye irritation: in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2000-02-08 to 2000-03-23
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Well documented, scientifically sound study according to a method similar to OECD guideline 405 with a few deviations. However, not GLP, no information on environmental conditions, individual eye endpoints (cornea, iris, conjunctiva) not reported in the results.
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 405 (Acute Eye Irritation / Corrosion)
Deviations:
yes
Remarks:
not GLP, no information on environmental conditions, individual eye endpoints (cornea, iris, conjunctiva) were not reported in the results
GLP compliance:
no
Species:
rabbit
Strain:
New Zealand White
Details on test animals or tissues and environmental conditions:
TEST ANIMALS
- Source: Biotech Co., Ltd
- Age at study initiation: 4 months old
- Weight at study initiation: 3.22-3.59 kg
- Housing: no data
- Diet (e.g. ad libitum): no data
- Water (e.g. ad libitum): no data
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): no data
- Humidity (%): no data
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): no data

IN-LIFE DATES: From: no data To: no data
Vehicle:
unchanged (no vehicle)
Controls:
other: right eyes were kept as controls
Amount / concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 0.1 g
- Concentration (if solution): not applicable

VEHICLE
- Amount(s) applied (volume or weight with unit): not applicable
- Concentration (if solution): not applicable
- Lot/batch no. (if required): not applicable
- Purity: not applicable
Duration of treatment / exposure:
single instillation
Observation period (in vivo):
1, 24, 48, and 72 hours
Number of animals or in vitro replicates:
3 animals (administered to the left eye of each animal)
Details on study design:
SCORING SYSTEM: According to Draize's standard (1959). Cornea, iris and conjunctiva were observed, and acknowledged damages were recorded. After calculating the total scores of each observation of each animal (Individual ocular irritation index, IOI) and the average score of each observation of each group (Mean ocular irritation index, MOI), the evaluation was made according to the AFNOR (1982) evaluation criteria. The acute ocular irritation index (AOI) was defined as the maximum of the MOI.

Accident Value Test of Corneal Epithelium: After the accident value test of anterior ocular segment done 24 hours after the application, corneal epithelium were dyed with fluorescein, and the stainability was evaluated.

TOOL USED TO ASSESS SCORE: hand-slit lamp
Irritation parameter:
other: MOI
Basis:
mean
Remarks:
of 3 animals
Time point:
other: 1 hour
Score:
4.7
Max. score:
110
Reversibility:
fully reversible within: 72 hours
Irritation parameter:
other: MOI
Basis:
mean
Remarks:
of 3 animals
Time point:
24 h
Score:
6
Max. score:
110
Reversibility:
fully reversible within: 72 hours
Irritation parameter:
other: MOI
Basis:
mean
Remarks:
of 3 animals
Time point:
48 h
Score:
2
Max. score:
110
Reversibility:
fully reversible within: 72 hours
Irritation parameter:
other: MOI
Basis:
mean
Remarks:
of 3 animals
Time point:
72 h
Score:
0
Max. score:
110
Reversibility:
other: not applicable
Irritation parameter:
other: AOI
Basis:
mean
Remarks:
of 3 animals
Time point:
24 h
Score:
6
Max. score:
110
Reversibility:
fully reversible within: 72 hours
Irritation parameter:
cornea opacity score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritation parameter:
iris score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritation parameter:
conjunctivae score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritation parameter:
chemosis score
Basis:
mean
Time point:
24/48/72 h
Remarks on result:
not measured/tested
Irritant / corrosive response data:
The AOI was determined to be 6.0 at 24 hours and the MOI after 48 hours was 2.0, therefore, this test agent was determined to be slightly irritating based on the AFNOR (1982) criteria. No irritation was observed after 72 hours.

The Accident Value Test of Corneal Epithelium 24 hours after application was zero in all three animals.
Other effects:
There were no abnormalities in the general condition or the weight changes to any of the 3 animals.
Interpretation of results:
GHS criteria not met
Conclusions:
The test agent was determined to be slightly irritating based on the AFNOR criteria. It does however not need to be classified for eye irritation according to the CLP criteria.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

1. Information on zirconium dioxide

Skin irritation / corrosion:

One reliable study was identified (BIBRA, 1986). This GLP study was performed according to the OECD Guideline 404 with minor deviations. The substance was determined not to be irritating to New Zealand White rabbit skin after 4 hours of exposure.

Eye irritation:

A reliable study is available for the read across substance yttrium zirconium oxide (Chemical Evaluation and Research Institute, 2000), i.e. zirconia stabilised with a small amount of yttria. The study was performed in New Zealand White rabbit according to a method equivalent to OECD Guideline 405 with some minor deviations. The test substance was determined to be slightly irritating based on the AFNOR criteria. Observed effects were fully reversible within 72 hours. However, the substance does not need to be classified for eye irritation according to the rules of the DSD and CLP Regulation.

2. Information on magnesium oxide

For magnesium oxide results were included from skin and eye irritation tests performed with magnesium hydroxide. The rationale for this is that in the presence of moisture magnesium oxide will form magnesium hydroxide according to the following reaction:

MgO + H2O <--> Mg (OH)2

Skin irritation / corrosion:

Two in vitro studies performed with magnesium hydroxide were added to the weight of evidence approach to cover the endpoint for skin irritation/corrosion potential.

The in vitro skin corrosion test was performed according to OECD Guideline 431 (reconstructed human epidermis test method) (Buskens, 2010a). The possible corrosive potential was tested using topical application for either 3 minutes or 1 hour. The mean relative tissue viabilities after 3 minute and 1 hour treatments were 88% and 95%, respectively. Because the mean relative tissue viability was not below 50% after the 3 minute treatment or 15% after the 1 hour treatment, it was concluded that magnesium hydroxide is not corrosive under the conditions of this test.

In the in vitro skin irritation test (OECD Guideline 439, reconstructed human epidermis test method) (Buskens, 2010b), the possible skin irritation potential of magnesium hydroxide was tested using topical application for 15 minutes, followed by a 42-h incubation period. The mean relative tissue viability after 15 minutes of treatment was 91%. Because the substance was found to be non-corrosive in the OECD 431 study and because the mean relative tissue viability was not below 50% in the OECD 439 study, the substance can be concluded not to be classified as irritating to skin. These findings are considered representative for magnesium oxide too.

Eye irritation

One in vitro and one in vivo study performed with magnesium hydroxide were added to the weight of evidence approach to cover the endpoint for eye irritation potential.

The in vitro eye irritation study was performed according to OECD Guideline 437 (BCOP test) (Verspeek-Rip, 2010a). Magnesium hydroxide yielded a mean in vitro irritancy score of 5.1 after 240 minutes of treatment. Since this score is below 55 and higher than 3, no final conclusion could be drawn and further in vitro (or in vivo testing) was required.

An in vivo study was performed in New Zealand White rabbit according to OECD Guideline 405 (van Otterdijk, 2010b). Magnesium hydroxide was determined not to be irritating based on the AFNOR criteria. Therefore the substance does not need to be classified for eye irritation according to the rules of the DSD and CLP Regulation.

Here too, these findings are considered representative for magnesium oxide.

3. Conclusion on magnesium zirconium oxide

Based on the available data for the individual constituents in the crystal lattice, it can be concluded that magnesium zirconium oxide is not irritating to skin or eyes and does not need to be classified for these endpoints.

Justification for classification or non-classification

1. Information on zirconium dioxide

Skin irritation / corrosion:

Based on the available data and according to the criteria of the CLP Regulation, this substance should not be classified for skin corrosion / irritation.

Serious eye damage / eye irritation:

Based on the available data and according to the criteria of the CLP Regulation, this substance should not be classified for serious eye damage / eye irritation.

2. Information on magnesium oxide

Skin irritation / corrosion:

Based on to the available data and according to the criteria of the CLP Regulation, this substance should not be classified for skin corrosion / irritation.

Serious eye damage / eye irritation:

Based on the available data and according to the criteria of the CLP Regulation, this substance should not be classified for serious eye damage / eye irritation.

3. Conclusion on magnesium zirconium oxide

Magnesium zirconium oxide is a stabilised zirconia, whereby zirconium dioxide and magnesium oxide are incorporated in a single crystal lattice. Based on the available data for the individual components zirconium dioxide and magnesium (hydr)oxide, neither of which are classified for local effects in skin or eyes, magnesium zirconium oxide can be concluded to be not classified for local effects in skin or eyes, according to the criteria of the CLP Regulation.