Palladium dihydroxide

Endpoint summary

Description of key information

In in vitro studies according to OECD431 and OECD439, Palladium dihydroxide was shown to be non corrosive and non-irritant to skin according to UN GHS and EU CLP regulation.

Palladium dihydroxide is considered to fall within the scope of the read-across category of 'Palladium, Palladium monoxide and Palladium dihydroxide'. Palladium monoxide was not irritant in a limited (pre-GLP) study, involving 24-hr occluded application to the intact and abraded skin of 6 male rabbits.

The eye irritation/corrosion potential of palladium dihydroxide was tested in two in vitro assays (OECD437 and OECD492). However, under the experimental conditions reported, a prediction for the eye damage hazard could not be made (GHS) for Palladium dihydroxide.

Palladium dihydroxide is considered to fall within the scope of the read-across category of 'Palladium, Palladium monoxide and Palladium dihydroxide'. According to an expert review of an unpublished eye irritation study, conducted to US guidelines (CFR 21, part 191 12), a single instillation of palladium monoxide (100 mg) to the eyes of six rabbits produced no signs of irritation.

The water solubility and dermal bioaccessibility of palladium dihydroxide was low (Skaeff 2012; O'Connor 2011). Although the dermal bio-elution testing does not extend to the use of simulation lachrymal fluid, the available simulation dermal fluid data is nevertheless indicative of negligible bioavailability following exposure via the eyes. Since a chemical is required to be bioavailable in order to induce (non-mechanical) irritation, and since the substance has no pH <2 or >11, palladium dihydroxide is considered incapable of inducing eye corrosion. Therefore, and driven by the inconclusive in vitro data, the registrants consider it justified to not perform further in vivo mammalian testing but instead classify the substance as Eye Irritant cat 2 (H319).

Key value for chemical safety assessment

Skin irritation / corrosion

Link to relevant study records

Reference

Reference 1

Endpoint:

skin irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not stated in paper, but submitted for publication in 1974

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Although the study is not conducted to a modern protocol and is somewhat limited, it is nevertheless fairly well documented and scientifically acceptable

Qualifier:

no guideline followed

Principles of method if other than guideline:

Dermal irritancy asessed using male albino rabbits using procedures and evaluation criteria adopted from those in use by the National Institute for Occupational Safety and Health, ... a modification of the official Food and Drug Administration procedure [1973]"

GLP compliance:

no

Remarks:

prior to GLP

Species:

rabbit

Strain:

other: albino

Details on test animals or test system and environmental conditions:

no data

Type of coverage:

occlusive

Preparation of test site:

other: Pairs of test sites, each 2 cm x 2 cm, on the closely clipped dorsolaterals aspects of each animal, one side abraded and the other side intact

Vehicle:

water

Remarks:

0.1 ml

Controls:

yes, concurrent vehicle

Amount / concentration applied:

0.1 g

Duration of treatment / exposure:

24 hours

Observation period:

skin reactions scored immediately on removal of patch and 48 hours later

Number of animals:

Total of 6 rabbits, with up to 7 pairs of test sites each, used to test 14 test substances, some substances tested more than once

Details on study design:

Pairs of test sites, each 2 cm x 2 cm, on the closely clipped dorsolaterals aspects of each animal, one side abraded and the other side intact; Test substances in solid (powder) state were mixed with water (0.1 g quantity mixed with 0.1 ml deionised water) and spread over each site; after application of test substances [several probably tested simultaneously on each animal], test sites occluded; 24 hours later, coverings removed and test sites gently washed with soap, rinsed and dried; skin reactions scored immediately and 48 hours later; evaluation on a grading scale from 0 to 4 [similar to Draize scale]

Irritation parameter:

overall irritation score

Basis:

mean

Remarks:

single test rating or average of two or three

Time point:

other: 24 and 72 hours

Score:

0

Max. score:

4

Remarks on result:

other: Severity rating for both intact and abraded skin sites

Irritant / corrosive response data:

Average skin reaction for 24 and 72 hours after the start of treatment calculated for intact and abraded skin [no individual scores or any further information presented in paper]

Interpretation of results:

GHS criteria not met

Conclusions:

Palladium monoxide was not irritant in a limited (pre-GLP) study, involving 24-hr occluded application to the intact and abraded skin of 6 male rabbits.

Executive summary:

In a pre-GLP study, the dermal irritancy of 14 materials, including palladium monoxide, was assessed in albino rabbits. Test materials, mixed with water, were applied to intact and abraded skin of 6 male albino rabbits as 24-hour occluded patches. Coverings were then removed and sites scored immediately and 48 hours later, using a scale from 0 (non-irritant) to 4 (corrosive).

Palladium monoxide failed to give any indication of irritation (score 0) on both intact and abraded skin (mean of reactions at 24 and 72 hours).

Reference 2

Endpoint:

skin irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

8 Oct 2020-18 Nov 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: MatTek Corporation Protocol: In vitro EpiDermTM Skin Irritation Test (EPI-200-SIT) For use with MatTek Corporation’s Reconstructed Human Epidermal Model EpiDerm (EPI-200-SIT); Version 10 February 2019

Qualifier:

according to guideline

Guideline:

EU Method B.46 (In Vitro Skin Irritation: Reconstructed Human Epidermis Model Test)

Version / remarks:

6 July 2012

Qualifier:

according to guideline

Guideline:

OECD Guideline 439 (In Vitro Skin Irritation: Reconstructed Human Epidermis Test Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test system:

human skin model

Remarks:

The EpiDerm™ tissue consists of normal, human-derived epidermal keratinocytes which have been cultured to form a multilayered, highly differentiated model of the human epidermis.

Source species:

human

Cell type:

other: EpiDerm™ tissue consists of organised basal, spinous and granular layers, and a multi-layered stratum corneum containing intercellular lamellar lipid layers arranged in patterns analogous to those found in vivo.

Vehicle:

unchanged (no vehicle)

Remarks:

The test item was crushed and ground in a mortar and with a pestle to improve the consistency. The test item was tested neat.

Details on test system:

Epi-200-SIT kits and MTT-100 assays are purchased from MatTek Corporation (82105 Bratislava, Slovakia). The EpiDerm™ tissue consists of normal, human-derived epidermal keratinocytes which have been cultured to form a multilayered, highly differentiated model of the human epidermis. It consists of organised basal, spinous and granular layers, and a multi-layered stratum corneum containing intercellular lamellar lipid layers arranged in patterns analogous to those found in vivo. The EpiDerm™ tissues (surface 0.6 cm²) are cultured on specially prepared cell culture inserts (MILLICELL, 10 mm ∅).
EpiDerm™ tissues are shipped with cool packs on medium-supplemented agarose gels in a 24-well plate. Including time in transit, tissues may be stored at 4 °C for up to 6 days prior to use.

Pre-Experiment
Test items which might absorb light in the same range as formazan dye (naturally or after treatment) and test items which might be able to directly reduce the vital dye MTT (to MTT formazan) may interfere with the tissue viability measurements and need the use of additional controls for corrections. Therefore, two pre-experiments were performed to determine the color interference and the MTT interference.

Option for the Main Experiment
Since the test item/ water or test item/ isopropanol solutions changed color significantly in the first pre-experiment and interfered with MTT in the second pre-experiment, the main experiment had to be performed with additional viable, freeze killed and an additional third set of controls in order to avoid double correction. These additional tissues were designated Non-Specific Killed Control (NSKC) and run in duplicates. They are freeze-killed tissues which were treated with the test item but incubated in medium without MTT solution in the MTT assay. At the end Data Correction Procedure III was performed.

Main Experiment
1 Pre-warming of EpiDerm™ Tissues
The plastic bag containing the 24-well plate with epidermal tissues was opened under sterile conditions. Under an airflow using forceps, the gauze was removed, and the inserts were taken out. Any remaining agarose that adheres to the outer sides of the inserts was removed by gentle blotting on the sterile filter paper or gauze and prior to the exposure of the test item and of the controls the EpiDerm™ tissues was inspected for quality:
It was taken care, that
• air bubbles between agarose and insert were not > 30% of the total surface,
• liquid on top of the insert was removed with sterile cotton tips,
• if again moisture was observed on top of the inserts after the pre-incubation or in case of visible defects the respective skin models was discarded.
The inserts with the EpiDerm™ tissues were transferred into 6-well-plates containing 0.9 ml assay medium and incubated for 60 minutes under standard conditions. Afterwards, the medium was changed and a further pre-incubation for 17 - 23 hours at standard incubation conditions follows.

2 Treatment
After pre-warming of the EpiDerm™ tissues was completed, the negative and positive control, and the test item was added atop the tissues. The test item respectively controls were tested in triplicate tissues with an exposure time of 60 minutes. Within this period the 6-well plates were placed in the incubator for 35 minutes at standard incubation conditions. In the remaining period the plates were placed in a sterile bench at room temperature until the end of treatment.
The test item was crushed and ground in a mortar and a pestle to improve the consistency. 25 mg (39.7 mg/cm2 according to guideline) of the test item was applied onto the surface of the tissue. The tissues were wetted with 25 μL DPBS prior to application.
At the end of the treatment interval the tissues were gently rinsed with PBS several times in order to remove any residual test material. Excess PBS was removed by gently shaking the inserts and blotting the bottom with blotting paper. Afterwards, the tissues were incubated in 0.9 mL of fresh assay medium for 24 hours. After this incubation period the medium was changed, and the tissues were incubated for another 18 ± 2 hours at standard incubation conditions. The complete incubation time was about 42 hours.

MTT-Assay
24-well plates were prepared with 300 μl MTT solution per well kept under standard conditions until required.
After the incubation period was completed, the tissues were transferred to the MTT-plates. After a 3 hour ± 5 minutes incubation period under standard conditions the tissues were rinsed with PBS and carefully dried with blotting paper.
The tissues were transferred into new 24-well plates containing 2 mL of extractant solution (isopropanol) in each well ensuring that the tissues were completely covered. The 24-well plates were sealed to minimise isopropanol evaporation. The formazan salt was extracted within 2-4 hours while shaking at room temperature.
At the end of the extraction period the inserts were pierced with an injection needle to allow the extract to run into the well from which the insert was taken, and the insert were discarded.
Per each tissue, 3 × 200 μL aliquots of the formazan solution were transferred into a 96-well, flat bottom, microtiter plate. 200 μL of isopropanol were added to the wells designated as blanks for 96-well plate.

Measurement
The optical density (OD570nm) was determined spectrophotometrically in duplicates by a microplate reader (Versamax® Molecular Devices). The absorbance values were determined using the software SoftMax Pro Enterprise (version 4.7.1).

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

30 μL of positive control or negative control, or25 mg test item were applied on triplicate tissues.

Duration of treatment / exposure:

The test item respectively controls were tested with an exposure time of 60 minutes.

Number of replicates:

The test item respectively controls were tested in triplicate tissues .

Irritation / corrosion parameter:

% tissue viability

Value:

78.94

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Interpretation of results:

GHS criteria not met

Conclusions:

In this study according to OECD439 and under the experimental conditions reported, Palladium dihydroxide is non-irritant to skin according to UN GHS and EU CLP regulation.

Executive summary:

This in vitro study in accordance with OECD439 was performed to assess the irritation potential of Palladium dihydroxide by means of the Human Skin Model Test with EpiDermTM tissue models.
The test item proved to be a MTT reducer in the MTT interference pre-experiment. Also, it dyed deionised water (pre-test for colour interference). Therefore, additional tests with freeze-killed tissues, viable tissues (without MTT addition) and non-specific killed controls (NSKC) had to be performed to determine correction factors for calculating the true viability in the main experiment.
Triplicate tissues of the human skin model EpiDerm™ were treated with the test item, the negative control (DPBS) or the positive control (5% SDS) for 60 minutes.
After treatment with the negative control the absorbance values were well within the required range of the acceptability criterion of mean OD ≥ 0.8 and ≤ 2.8 for the 60 minutes treatment interval, thus assuring the quality of the tissues.
Treatment with the positive control induced a sufficient decrease in the viability as compared to the negative control for the 60 minutes treatment interval, thus assuring the validity of the test system.
After exposure of the tissues to Palladium dihydroxide the mean relative viability value was 78.94% compared to the relative absorbance value of the negative control. This value is above the threshold for irritancy of ≤ 50%. Therefore, the test item is not considered to possess an irritant potential.
In conclusion, it can be stated that in this study and under the experimental conditions reported, Palladium dihydroxide is non-irritant to skin.

Reference 3

Endpoint:

skin corrosion: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

11 Sept 2020-16 Dec 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: MatTek test protocol “In vitro EpiDermTM Skin Corrosion Test (EPI-200-SCT)”, 07 November 2014.

Qualifier:

according to guideline

Guideline:

EU Method B.40 (In Vitro Skin Corrosion: Transcutaneous Electrical Resistance Test (TER))

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test system:

human skin model

Remarks:

The EpiDerm™ tissue consists of normal, human-derived epidermal keratinocytes which have been cultured to form a multilayered, highly differentiated model of the human epidermis.

Source species:

human

Cell type:

other: The EpiDerm™ tissue consists of organised basal, spinous and granular layers, and a multi-layered stratum corneum containing intercellular lamellar lipid layers arranged in patterns analogous to those found in vivo.

Vehicle:

unchanged (no vehicle)

Remarks:

The test item was crushed and ground in a mortar and with a pestle to improve the consistency. The test item was tested neat.

Details on test system:

Reconstructed Human EpiDerm model purchased from MatTek
Epi-200 SCT kits and MTT-100 assays are purchased from MatTek Corporation (Bratislava, Slovakia). The EpiDerm™ tissue consists of normal, human-derived epidermal keratinocytes which have been cultured to form a multilayered, highly differentiated model of the human epidermis. It consists of organised basal, spinous and granular layers, and a multi-layered stratum corneum containing intercellular lamellar lipid layers arranged in patterns analogous to those found in vivo. The EpiDerm™ tissues (surface 0.6 cm²) are cultured on specially prepared cell culture inserts (MILLICELL, 10 mm ∅).
EpiDerm™ tissues are shipped on cool packs and on medium-supplemented agarose gels in a 24-well plate. Including time in transit, tissues may be stored at a specified storage for up to 6 days prior to use.

Standard Culture Conditions
Each incubation of the tissues was performed at 37 ± 1.5°C and 5 ± 0.5% CO2 in DMEM Medium.

Pre-Experiment
Test items which might absorb light in the same range as formazan dye (naturally or after treatment) and test items which might be able to directly reduce the vital dye MTT (to MTT formazan) may interfere with the tissue viability measurements and need the use of additional controls for corrections. Therefore, two pre-experiments, were performed to determine the color interference and the MTT interference.

Options for the Main Experiment
Since the test item/ water or test item/ isopropanol solutions change color significantly and interferes with MTT in the pre-experiment, the test had to be performed with the controls mentioned in version d of the General Study Plan. The following additional controls were necessary for Data Correction:
• DPBS treated tissues (NC_CC)
• Test item treated tissues (TI_CC)
• DPBS treated freeze-killed tissues (NC_KC)
• Test item treated freeze-killed tissues (TI_KC)
• Test item treated freeze-killed tissues (TI_NSKC)
In this experimental set-up, Data Correction Procedure III had to be performed.

Main Experiment
1 Pre-warming of EpiDerm™ Tissues
The plastic bag containing the 24-well plate with epidermal tissues was opened under sterile conditions. Under an airflow using forceps, the gauze was removed and the inserts were taken out. Any remaining agarose that adheres to the outer sides of the inserts was removed by gentle blotting on the sterile filter paper or gauze and prior to the exposure of the test item and of the controls the EpiDerm™ tissues was inspected for quality:
It was taken care, that
• air bubbles between agarose and insert were not > 30% of the total surface,
• liquid on top of the insert was removed with sterile cotton tips,
• if again moisture was observed on top of the inserts after the pre-incubation or in case of visible defects the respective skin models was discarded.
The inserts with the EpiDerm™ tissues were transferred into 6-well-plates containing 0.9 ml assay medium and incubated for approx. 18 h under standard conditions.

2 Treatment
After the pre-warming of the EpiDermTM tissues is completed, the DMEM-based medium in each well was replaced with 0.9 mL fresh assay medium.
The test item respectively controls were tested in duplicate tissues with exposure times of 3 ± 0.5 minutes and 60 ± 5 minutes. The 6-well plates for the 3 minutes exposure periods were stayed at room temperature in the sterile bench, the 6-well plates for the 60 minutes exposure period were incubated under standard conditions.
The tissues were wetted with 25 μL DPBS prior to application. Approximately 25 mg (39.7 mg/cm2 according to guideline) of the test item were applied onto the surface of the tissue.
At the end of the exposure period the tissues were removed from the 6-well plate and gently rinsed with PBS to remove any residual test material for several times. Excess PBS was removed by gently shaking the tissue insert and blotting the lower surface with blotting paper. The tissues were placed in the prepared holding plate until all tissues have been rinsed.

3 MTT Assay
24-well plates were prepared with 300 μl MTT solution (and only medium for the additional DPBS treated tissues (NC_CC), Test item treated tissues (TI_CC) and NSKC tissues) and kept under standard conditions until required.
Following rinsing, the tissue inserts were transferred from the holding plates to the MTT-plates. After a 3 hour incubation period under standard conditions the tissues were rinsed with PBS and carefully dried with blotting paper.
The tissues were transferred into new 24-well plates containing 2 mL of extractant solution (isopropanol) in each well ensuring that the tissues were completely covered. The 24-well plates were sealed to minimise isopropanol evaporation. The formazan salt was extracted for 4-72 h in the refrigerator at 2-8°C without shaking. At the end of the extraction period the inserts were pierced with an injection needle to allow the extract to run into the well from which the insert was taken, and the inserts were discarded. Subsequently, the plates were shaken for 15 min at room temperature. Additionally, the solution was homogenized by a pipette before transferred into a 96-well plate. Per each tissue, 3 × 200 μL aliquots of the formazan solution were transferred in a flat bottom, microtiter plate. 200 μL of isopropanol were added to the wells designated as blanks for 96-well plate.

Measurement
The optical density (OD570nm) of the formazan extract is determined spectrophotometrically by a microplate reader (Versamax® Molecular Devices). The absorbance values will be determined using the software SoftMax Pro Enterprise (version 4.7.1).

Control samples:

yes, concurrent negative control

yes, concurrent positive control

Amount/concentration applied:

50 μL of the controls were applied to each set of duplicate tissues for the 3 min and 1 hour exposure periods.
Approximately 25 mg (39.7 mg/cm2 according to guideline) of the test item were applied onto the surface of the tissue.

Duration of treatment / exposure:

The test item respectively controls were tested with exposure times of 3 ± 0.5 minutes and 60 ± 5 minutes.

Number of replicates:

The test item respectively controls were tested in duplicate tissues.

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

60 min exposure

Value:

100.75

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Irritation / corrosion parameter:

% tissue viability

Run / experiment:

3 min exposure

Value:

99.59

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

no indication of irritation

Interpretation of results:

GHS criteria not met

Conclusions:

In this study in accordance with OECD431 and under the reported experimental conditions, Palladium dihydroxide is non-corrosive to skin according to EU CLP and UN GHS.

Executive summary:

This in vitro study in accordance with OECD 431 was performed to assess the corrosive potential of Palladium dihydroxide by means of the Human Skin Model Test with EpiDerm™ tissues models.
The test item reduced MTT (pre-test for direct MTT reduction), and it changed colour when mixed with deionised water (pre-test for colour interference). Consequently, additional tests with freeze-killed, viable tissues and Non-Specific Killed Tissues to determine correction factors for calculating the true viability in the main experiment were necessary.
Independent duplicate tissues of EpiDerm™ were exposed to either the test item, the negative control (Dulbecco's Phosphate-Buffered Saline (DPBS)) or the positive control (8.0 N KOH) for 3 minutes and 1 hour, respectively.
After exposure to the negative control the absorbance values met the required acceptability criterion of a mean OD570 ≥ 0.8 and ≤ 2.8 for both treatment intervals thereby confirming the acceptable quality of the tissues.
Exposure to the positive control induced a decrease in the relative absorbance as compared to the negative control, both for the 3 minutes exposure period (8.64%) and for the 1 hour exposure period (2.75%) thus confirming the validity of the test system and the specific batch of tissue models. The CV in the range 20 – 100% viability between the tissue replicates is ≤ 30%, thus the validity of the test system and the specific batch of the tissue models is confirmed.
After exposure of the tissues to the test item the relative absorbance value was 99.59% after 3 minutes exposure. After 1 hour exposure the relative absorbance value was 100.75%. Both values did not reach the threshold for corrosivity which is defined to be < 50% after the 3 minutes exposure or ≥ 50% after 3 minutes exposure and < 15% after the 1 hour exposure. Therefore, the test item is considered to be not corrosive.
In conclusion, it can be stated that in this study and under the reported experimental conditions, the test item Palladium dihydroxide is non-corrosive to skin according to EU CLP and UN GHS.
The required acceptability criteria were met.

Reference 4

Endpoint:

skin irritation: in vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

not stated in paper, but submitted for publication in 1974

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Although the study is not conducted to a modern protocol and is somewhat limited, it is nevertheless fairly well documented and scientifically acceptable

Justification for type of information:

Substance considered to fall within the scope of the read-across category 'Palladium, Palladium monoxide and Palladium dihydroxide'

Reason / purpose for cross-reference:

read-across source

Qualifier:

no guideline followed

Principles of method if other than guideline:

Dermal irritancy asessed using male albino rabbits using procedures and evaluation criteria adopted from those in use by the National Institute for Occupational Safety and Health, ... a modification of the official Food and Drug Administration procedure [1973]"

GLP compliance:

no

Remarks:

prior to GLP

Species:

rabbit

Strain:

other: albino

Details on test animals or test system and environmental conditions:

no data

Type of coverage:

occlusive

Preparation of test site:

other: Pairs of test sites, each 2 cm x 2 cm, on the closely clipped dorsolaterals aspects of each animal, one side abraded and the other side intact

Vehicle:

water

Remarks:

0.1 ml

Controls:

yes, concurrent vehicle

Amount / concentration applied:

0.1 g

Duration of treatment / exposure:

24 hours

Observation period:

skin reactions scored immediately on removal of patch and 48 hours later

Number of animals:

Total of 6 rabbits, with up to 7 pairs of test sites each, used to test 14 test substances, some substances tested more than once

Details on study design:

Pairs of test sites, each 2 cm x 2 cm, on the closely clipped dorsolaterals aspects of each animal, one side abraded and the other side intact; Test substances in solid (powder) state were mixed with water (0.1 g quantity mixed with 0.1 ml deionised water) and spread over each site; after application of test substances [several probably tested simultaneously on each animal], test sites occluded; 24 hours later, coverings removed and test sites gently washed with soap, rinsed and dried; skin reactions scored immediately and 48 hours later; evaluation on a grading scale from 0 to 4 [similar to Draize scale]

Irritation parameter:

overall irritation score

Basis:

mean

Remarks:

single test rating or average of two or three

Time point:

other: 24 and 72 hours

Score:

0

Max. score:

4

Remarks on result:

other: Severity rating for both intact and abraded skin sites

Irritant / corrosive response data:

Average skin reaction for 24 and 72 hours after the start of treatment calculated for intact and abraded skin [no individual scores or any further information presented in paper]

Interpretation of results:

not irritating

Remarks:

Migrated information Criteria used for interpretation of results: other: evaluation criteria adopted from those in use by the National Institute for Occupational Safety and Health

Conclusions:

Palladium monoxide was not irritant in a limited (pre-GLP) study, involving 24-hr occluded application to the intact and abraded skin of 6 male rabbits.

Executive summary:

In a pre-GLP study, the dermal irritancy of 14 materials, including palladium monoxide, was assessed in albino rabbits. Test materials, mixed with water, were applied to intact and abraded skin of 6 male albino rabbits as 24-hour occluded patches. Coverings were then removed and sites scored immediately and 48 hours later, using a scale from 0 (non-irritant) to 4 (corrosive).

Palladium monoxide failed to give any indication of irritation (score 0) on both intact and abraded skin (mean of reactions at 24 and 72 hours).

The substance is considered to fall within the scope of the read-across category 'Palladium, Palladium monoxide and Palladium dihydroxide'

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Link to relevant study records

Reference

Reference 1

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

13 Nov 2020-17 Dec 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU method B.47 (Bovine corneal opacity and permeability test method for identifying ocular corrosives and severe irritants)

Version / remarks:

9.12.2010

Qualifier:

according to guideline

Guideline:

OECD Guideline 437 (Bovine Corneal Opacity and Permeability Test Method for Identifying i) Chemicals Inducing Serious Eye Damage and ii) Chemicals Not Requiring Classification for Eye Irritation or Serious Eye Damage)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Species:

cattle

Details on test animals or tissues and environmental conditions:

Test System: Freshly isolated bovine cornea (14 month old donor cattle)
Source: AB Schlachthof GmbH & Co. KG, 63739 Aschaffenburg, Germany

Collection of Bovine Eyes
Freshly isolated bovine eyes of donor cattle were collected from the abattoir. Excess tissue was removed from the excised eyes. The isolated eyes were stored in HBSS (Hank’s Balanced Salt Solution) containing 1% (v/v) penicillin/streptomycin (100 units/mL penicillin and 100 μg/mL streptomycin) in the cooled slaughter-house and during transportation on the same morning to the laboratory using a Styrofoam box. The corneas were isolated on the same day after delivery of the eyes.

Preparation of Corneas
All eyes were carefully examined macroscopically for defects. Those presenting defects such as vascularization, pigmentation, opacity and scratches were discarded. The cornea was carefully removed from the eye using scalpel and rounded scissors. A rim of about 2 mm of tissue (sclera) was left for stability and handling of the isolated cornea. The corneas were directly used in the BCOP test on the same day.
Each isolated cornea was mounted in a specially designed cornea holder according to the description given in OECD guideline 437, which consists of anterior and posterior compartments, which interface with the epithelial and the endothelial sides of the cornea, respectively. The endothelial side of the cornea was positioned against the sealing ring (O-ring) of the posterior part of the holder. The cornea was gently flattened over the O-ring but stretching was avoided. The anterior part of the holder was positioned on top of the cornea and fixed in place with screws. Both compartments of the holder were filled with incubation medium. The posterior compartment was filled first to return the cornea to its natural convex position. Care was taken to assure that no air bubbles were present within the compartments.
For equilibration, the corneas in the holder were incubated in a vertical position for about one hour at 32 ± 1 °C in a water-bath. At the end of the incubation period, the medium was changed before basal opacity measurement (t0). Only corneas with a value of the basal opacity < 7 were used. Sets of three corneas were used for treatment with the test item and for the negative and positive controls, respectively.

Vehicle:

physiological saline

Remarks:

The test item was ground in a mortar with a pistil to improve its consistency and tested as a 20% suspension (w/v) in saline using sonication for 10 minutes.

Controls:

yes, concurrent vehicle

yes, concurrent positive control

Amount / concentration applied:

The anterior compartment received the test item suspension or the negative or positive controls at a volume of 0.75 mL each on the surface of the corneas via open chamber method, respectively.

Duration of treatment / exposure:

The corneas were incubated in a horizontal position at 32 ± 1 °C in the water-bath for 240 minutes.

Duration of post- treatment incubation (in vitro):

After exposure, the test item or the control items, respectively, were each rinsed off from the according application sides with EMEM containing phenol red for at least three times or more until phenol red was still discoloured (yellow or purple), or the test item was still visible. Since the test item proved difficult to remove by the rinsing method, the front cover of the holder was opened and the cornea was carefully washed using a gentle stream of incubation medium. Once the medium was free of the test item the corneas were given a final rinse with cMEM without phenol red.

Number of animals or in vitro replicates:

3 corneas per group (pos control, neg control, test item) were used.

Details on study design:

Opacity Measurement
The opacitometer determines changes in the light transmission passing through the corneas and displays a numerical opacity value.

Permeability Determination
Following to the opacity readings, the permeability endpoint was measured as an indication of the integrity of the epithelial cell sheets. After the final opacity measurement was performed, the incubation medium was removed from both chambers. The posterior chamber was filled with fresh cMEM first. Then the anterior compartment was filled with 1 mL of a 0.5% (w/v) sodium fluorescein solution in HBSS. Corneas were incubated again in a horizontal position for 90 ± 5 minutes in a water-bath at 32 ± 1 °C. Incubation medium from the posterior compartment was removed, well mixed and transferred into a 96 well plate. The optical density was measured with a microplate reader (Versamax® Molecular Devices) at 490 nm (OD490). The absorbance values were determined using the software SoftMax Pro Enterprise (version 4.7.1).

Irritation parameter:

in vitro irritation score

Value:

5.87

Vehicle controls validity:

valid

Negative controls validity:

not applicable

Positive controls validity:

valid

Remarks on result:

other: No prediction can be made

Interpretation of results:

other: No prediction can be made

Conclusions:

According to the current study (in accordance to OECD437) and under the experimental conditions reported, a prediction for the eye damage hazard cannot be made (GHS) for Palladium dihydroxide.

Executive summary:

This in vitro study was performed to assess the corneal irritation and damage potential of Palladium dihydroxide by means of the BCOP assay using fresh bovine corneas.
Sets of three corneas were used for treatment with the test item (Palladium dihydroxide as a 20% (w/v) suspension in saline (0.9% (w/v) NaCl in deionised water)) and for the negative and positive controls. Prior to treatment, opacity was measured in the fresh bovine corneas following equilibration (t0). 0.75 mL of the test item, positive or negative controls were each applied to different corneas fixed in an incubation chamber. The corneas were then incubated in a horizontal position for 240 minutes at 32 ± 1 °C. The posterior chamber contained incubation medium. After the incubation phase, the test item, the positive, and the negative controls were each rinsed from the corneas and opacity was measured again (t240).
After the opacity measurements, the posterior chamber was re-filled with fresh cMEM and then the anterior compartment was filled with 1 mL of a 0.5% (w/v) sodium fluorescein solution in HBSS. Corneas were incubated in a horizontal position for 90 minutes at 32 ± 1 °C and then the incubation medium from the posterior chamber was removed and transferred to a 96 well-plate. Permeability of the corneas was determined by assessing the transfer of sodium fluorescein after incubation, measured spectrophotometrically.
With the negative control (physiological saline), neither an increase of opacity nor permeability of the corneas was observed.
The positive control (10% (w/v) benzalkonium chloride in saline) showed clear opacity and increased permeability of the cornea, corresponding to a classification as serious eye damage (EU CLP/GHS Category 1).
Relative to the negative control, the test item Palladium dihydroxide caused an increase of the corneal opacity and permeability and the calculated mean in vitro irritancy score was 5.87. Since this value is between the cut-off values of 3 (threshold for no category) and 55 (threshold for serious eye damage) no prediction for corneal irritation and damage potential can be made according to OECD 437 (see table in chapter 3.9.3).
In conclusion, according to the current study and under the experimental conditions reported, a prediction for the damage hazard cannot be made (GHS) for Palladium dihydroxide.

Reference 2

Endpoint:

eye irritation: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

30 Nov 2020 - 2 Feb 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: MatTek Corporation Protocol: EpiOcular™ Eye Irritation Test (OCL-200-EIT) for the prediction of acute ocular irritation of chemicals; for use with MatTek Corporation’s Reconstructed Human EpiOcular™ Model; MK-24-007-005

Version / remarks:

29 June 2015

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 492 (Reconstructed Human Cornea-like Epithelium (RhCE) Test Method for Identifying Chemicals Not Requiring Classification and Labelling for Eye Irritation or Serious Eye Damage)

Version / remarks:

18 June 2019

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Purity: 97.4% (73.80% palladium)

Species:

other: The EpiOcular tissue construct is a non-keratinized epithelium prepared from normal human keratinocytes. It models the cornea epithelium with progressively stratified, but not cornified cells. These cells are not transformed or transfected with genes to i

Details on test animals or tissues and environmental conditions:

The EpiOcular tissue construct is a non-keratinized epithelium prepared from normal human keratinocytes. It models the cornea epithelium with progressively stratified, but not cornified cells. These cells are not transformed or transfected with genes to induce an extended life span in culture. The “tissue” is prepared in inserts (MILLICELL, 10 mm ∅) with a porous membrane through which the nutrients pass to the cells. A cell suspension is seeded into the insert in specialized medium. After an initial period of submerged culture, the medium is removed from the top of the tissue so that the epithelial surface is in direct contact with the air (surface 0.6 cm²). This allows the test item to be directly applied to the epithelial surface in a fashion similar to how the corneal epithelium would be exposed in vivo.

Each incubation of the tissues was performed under 37 ± 1.5°C and 5 ± 0.5% CO2 in DMEM Medium.

Standard Assay Kit and MTT-100 kit were purchased from MatTek Corporation (82105 Bratislava, Slovakia, Lot No.: 30688). The quality certificate of the test kits demonstrating its robustness is annexed to the study report.

Vehicle:

unchanged (no vehicle)

Remarks:

The test item was tested neat.

Controls:

yes, concurrent no treatment

yes, concurrent positive control

Amount / concentration applied:

Each 50 μL were applied on duplicate tissues for 6 hours.

Duration of treatment / exposure:

Each 50 μL were applied on duplicate tissues for 6 hours.

Number of animals or in vitro replicates:

Each 50 μL were applied on duplicate tissues for 6 hours.

Details on study design:

Pre-Experiment
Test items which might absorb light in the same range as formazan dye (naturally or after treatment) and test items which might be able to directly reduce the vital dye MTT (to MTT formazan) may interfere with the tissue viability measurements and need the use of additional controls for corrections. Therefore, two pre-experiments were performed to determine the color interference and the MTT interference.
1/1) The Color Interference – Test
Colored test items or test items which become colored after application to the tissues may interfere with the photometric MTT measurement if the colorant binds to the tissue and is extracted together with MTT. Therefore, each test item had to be checked for its colorant properties.
Therefore, 50 mg ± 2 of the test item was added to 1 mL of deionised water and mixed. 1 mL of deionised water was used as control (blank). Both were incubated for 60 min under standard conditions.
In parallel, 50 mg ± 2 of the test item was added to 2 mL of isopropanol and mixed. A control (2 mL of isopropanol, blank) was run concurrently. Both were incubated for 3 hours at room temperature.
Since the test item was not soluble in water or isopropanol the suspension was centrifuged.
After incubation the presence of the staining was evaluated by OD measurement (see section 5.5 Measurement).
2/The MTT Interference – Test
To test if a test item directly reduces MTT, 1 ml of a MTT solution (1 mg/mL) including 50 mg ± 2 of the test item was incubated for 180 min under standard conditions. 50 μL deionised water in MTT solution was used as negative control.
After incubation the change of color was determined by the unaided eye.

Since the OD of the test item in deionised water or isopropanol at 570 nm after blank correction was > 0.08 in the first pre-experiment and interfered with MTT in the second pre-experiment, the main experiment had to be performed with additional viable, freeze killed and an additional third set of controls in order to avoid double correction. These additional tissues were designated Non-Specific Killed Control (NSKC) and run in duplicates. They are freeze-killed tissues which were treated with the test item, but incubated in medium without MTT solution in the MTT assay.

Main Experiment
1/Pre-warming of EpiOcular™ Tissues
The plastic bag containing the 24-well plate with epidermal tissues was opened under sterile conditions. Under an airflow using forceps, the gauze was removed and the inserts were taken out. Any remaining agarose that adheres to the outer sides of the inserts was removed by gentle blotting on the sterile filter paper or gauze and prior to the exposure of the test item and of the controls the EpiOcular™ tissues was inspected for quality:
It was taken care, that
• air bubbles between agarose and insert were not > 30% of the total surface,
• liquid on top of the insert was removed with sterile cotton tips,
• if again moisture was observed on top of the inserts after the pre-incubation or in case of visible defects the respective skin models was discarded.
EpiOcularTM tissues were equilibrated at room temperature for 15 min. The inserts with the tissues were transferred into 6-well-plates containing 1.0 ml assay medium and incubated for 60 minutes under standard conditions. Afterwards, the medium was changed and a further pre-incubation for 16 - 24 hours at standard incubation conditions follows.
2 Treatment
After pre-warming of the EpiOcular™ tissues was completed, and prior to application of the test item respectively the controls, all tissues were pre-wetted with 20 μL Ca2+Mg2+free-DPBS and incubated for 30 min.
According to OECD guideline 492 a minimum of 83.3 mg/cm2 ≙ 50 mg for the solid test item were used for treatment.
The test item and the controls were tested in duplicate tissues. Concurrent negative and positive control were applied at a volume of 50 μL and for the test item 50 mg to the tissue surface and incubated for 6 h.
Afterwards all tissues were rinsed several times in 100 ml of Ca2+/Mg2+-free DPBS and incubated for 25 min in 5 ml assay medium in a 12-well plate at room temperature (post-exposure immersion). At the end of this incubation the tissues were transferred into a 6-well plate with 1 ml assay medium and incubated for a post-exposure incubation for 18 h at standard conditions.

MTT-Assay
Tissues treated with the test item were extracted from the bottom of the tissue only, to minimise any potential contamination of the isopropanol extraction solution with any test item that may have remained on the tissue. The concurrently tested negative and positive control substances were treated similarly to the tested item.
For the MTT-Assay, tissues were incubated for 180 min in 300 μl MTT solution. Additional viable or NSKC tissues were incubated in 300 μl medium under standard conditions. Each tissue was extracted with isopropanol within 2-4 h while shaking at room temperature. Then, the extracts were mixed and two 200 μL aliquots were transferred to a 96-well plate for OD measurement. 200 μL of isopropanol were added to the wells designated as blanks for 96-well plate.

Measurement
The optical density (OD570nm) was determined spectrophotometrically in duplicates by a microplate reader (Versamax® Molecular Devices). The absorbance values were determined using the software SoftMax Pro Enterprise (version 4.7.1).

Irritation parameter:

mean percent tissue viability 

Value:

34.24

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Remarks on result:

not determinable

Remarks:

After treatment with the test item, a mean relative viability value of 34.24% was measured compared to the relative absorbance value of the negative control. This value is below the threshold for irritancy of ≤ 60%. Therefore, no prediction can be made for Palladium dihydroxide from this result in isolation.

Interpretation of results:

study cannot be used for classification

Remarks:

This value is below the threshold for irritancy of ≤ 60%. Therefore, no prediction can be made for Palladium dihydroxide from this result.

Conclusions:

From the results of this Human Cornea Model Test under the experimental conditions reported, no prediction can be made for Palladium dihydroxide from this result in isolation.

Executive summary:

This in vitro study was performed to assess the eye irritation potential of Palladium dihydroxide by means of the Human Cornea Model Test.
The test item was directly applied to the epithelial surface of the EpiOcularTM tissue construct and following exposure, cell viability was measured by dehydrogenase conversion of MTT. The percent reduction of cell viability, in comparison of untreated negative controls, is used to predict eye irritation potential.
The test item proved to be a MTT reducer in the MTT interference pre-experiment. Also, it proved to dye water in the color interference pre-experiment since the OD of the test item in deionised water at 570 nm after blank correction was > 0.08. Therefore, additional tests with freeze-killed tissues, viable tissues and non-specific killed controls (NSKC) had to be performed. The viability values resulted in these additional tests were used to correct the values gained in the main experiment.
Each 50 mg of the test item or 50 μL of the negative control (deionised water) and of the positive control (methyl acetate), were applied to each duplicate tissue for 6 hours.
The mean OD of the tissue replicates treated with the negative control was > 0.8 and < 2.8, thus showing the quality of the tissues.
Treatment with the positive control induced a decrease below 50% viability compared with the negative control value in the relative absorbance, thus ensuring the validity of the test system.
The difference of relative viability between the two relating tissues was < 20 p.p. in the same run (for test item tissues, positive and negative control tissues).
After treatment with the test item a mean relative viability value of 34.24% was measured, compared to the mean value of the negative control. This value is below the threshold for irritancy of ≤ 60%. Therefore, no prediction can be made for Palladium dihydroxide from this result in isolation and additional information is required for classification purposes.
In conclusion, from the results of this Human Cornea Model Test under the experimental conditions reported, no prediction can be made for Palladium dihydroxide from this result in isolation.

Reference 3

Endpoint:

eye irritation: in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study (US CFR), pre-GLP, with limited reporting.

Qualifier:

according to guideline

Guideline:

other: CFR 21, part 191 12 (revised as of April 1, 1973)

Deviations:

no

GLP compliance:

no

Remarks:

(prior to GLP)

Species:

rabbit

Strain:

not specified

Details on test animals or tissues and environmental conditions:

Albino rabbits with no known ocular abnormalities.

Vehicle:

not specified

Controls:

other: The left eye of each animal served as a control.

Amount / concentration applied:

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 100 mg (deposited on the eye surface)

Duration of treatment / exposure:

Presumably the observation period

Observation period (in vivo):

3 days

Number of animals or in vitro replicates:

6

Details on study design:

REMOVAL OF TEST SUBSTANCE: Not removed

SCORING SYSTEM: No data

TOOL USED TO ASSESS SCORE: No data

Irritation parameter:

other: Number of animals showing irritant reactions

Basis:

other: Total number of test animals

Time point:

other: 24 hours

Score:

6

Max. score:

6

Reversibility:

not reversible

Irritation parameter:

other: Number of animals showing irritant reactions

Basis:

other: Total number of test animals

Time point:

other: 48 hours

Score:

6

Max. score:

6

Reversibility:

not reversible

Irritation parameter:

other: Number of animals showing irritant reactions

Basis:

other: Total number of test animals

Time point:

other: 72 hours

Score:

6

Max. score:

6

Reversibility:

not reversible

Irritant / corrosive response data:

All six animals receiving palladium dichloride showed corrosive conjunctival lesions and severe inflammation of the cornea and anterior chamber of the eye.

Other effects:

No data

Interpretation of results:

Category 1 (irreversible effects on the eye)

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

According to an expert review of an early unpublished eye irritation study, conducted to US guidelines (CFR 21, part 191 12), a single instillation of palladium dichloride (100 mg) to the eyes of six rabbits produced irreversible effects.

Executive summary:

According to an expert review of an early unpublished eye irritation study, conducted to US test guidelines (CFR 21, part 191 12), palladium dichloride (100 mg) was instilled into one eye of each of six rabbits. The other eye remained untreated and acted as the control. The treated eye was then assessed for ocular inflammation 24, 48 and 72 hr after application. All six animals showed severe conjunctival lesions and severe inflammation of the cornea and anterior chamber of the eye. The effects persisted throughout the observation period indicating that the test material induced irreversible effects on the eye.

 

Based on the results of this study, palladium dichloride should be classified as Category 1 (irreversible effects on the eye) according to EU CLP criteria (EC 1272/2008).

Reference 4

Endpoint:

eye irritation: in vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: US CFR guideline study, pre-GLP, with limited reporting.

Justification for type of information:

Substance considered to fall within the scope of the read-across category 'Palladium, Palladium monoxide and Palladium dihydroxide'

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

other: CFR 21, part 191 12 (revised as of April 1, 1973)

Deviations:

no

GLP compliance:

no

Remarks:

(prior to GLP)

Species:

rabbit

Strain:

not specified

Details on test animals or tissues and environmental conditions:

Albino rabbits with no known ocular abnormalities.

Vehicle:

not specified

Controls:

other: The left eye of each animal served as a control.

Amount / concentration applied:

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 100 mg (deposited on the eye surface)

Duration of treatment / exposure:

Presumably the observation period

Observation period (in vivo):

3 days

Number of animals or in vitro replicates:

6

Details on study design:

REMOVAL OF TEST SUBSTANCE: Not removed

SCORING SYSTEM: No data

TOOL USED TO ASSESS SCORE: No data

Irritation parameter:

other: Number of animals showing irritant reactions

Basis:

other: Total number of test animals

Time point:

other: 24 hours

Score:

0

Max. score:

6

Reversibility:

other: Not applicable

Irritation parameter:

other: Number of animals showing irritant reactions

Basis:

other: Total number of test animals

Time point:

other: 48 hours

Score:

0

Max. score:

6

Reversibility:

other: Not applicable

Irritation parameter:

other: Number of animals showing irritant reactions

Basis:

other: Total number of test animals

Time point:

other: 72 hours

Score:

0

Max. score:

6

Reversibility:

other: Not applicable

Irritant / corrosive response data:

No corrosive conjunctival lesions or severe inflammation of the cornea and anterior chamber of the eyes

Other effects:

In one animal, the test material was still present in the conjunctival sac at the end of the observation period, but was completely covered with a thick mucous material.

Interpretation of results:

not irritating

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

According to an expert review of an unpublished eye irritation study, conducted to US guidelines (CFR 21, part 191 12), a single instillation of palladium monoxide (100 mg) to the eyes of six rabbits produced no signs of irritation.

Executive summary:

According to an expert review of an unpublished eye irritation study, conducted to US test guidelines (CFR 21, part 191 12), palladium monoxide (100 mg) was instilled into one eye of each of six rabbits. The other eye remained untreated and acted as the control. The treated eye was then assessed for ocular inflammation 24, 48 and 72 hr after application. No reaction was noted in any of the six animals, indicating that the test material was not irritating.

 Based on the results of this study, palladium monoxide should not be classified for eye irritation according to EU CLP criteria (EC 1272/2008).

The substance is considered to fall within the scope of the read-across category 'Palladium, Palladium monoxide and Palladium dihydroxide'

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In in vitro studies according to OECD431 and OECD439, Palladium dihydroxide was shown to be non corrosive and non-irritant to skin according to UN GHS and EU CLP regulation.

Palladium dihydroxide is considered to fall within the scope of the read-across category of 'Palladium, Palladium monoxide and Palladium dihydroxide'. Palladium monoxide was not irritant in a limited (pre-GLP) study, involving 24-hr occluded application to the intact and abraded skin of 6 male rabbits.

The eye irritation/corrosion potential of palladium dihydroxide was tested in two in vitro assays (OECD437 and OECD492). However, under the experimental conditions reported, a prediction for the eye damage hazard could not be made (GHS) for Palladium dihydroxide.

Palladium dihydroxide is considered to fall within the scope of the read-across category of 'Palladium, Palladium monoxide and Palladium dihydroxide'. According to an expert review of an unpublished eye irritation study, conducted to US guidelines (CFR 21, part 191 12), a single instillation of palladium monoxide (100 mg) to the eyes of six rabbits produced no signs of irritation.

The water solubility and dermal bioaccessibility of palladium dihydroxide was low (Skaeff 2012; O'Connor 2011). Although the dermal bio-elution testing does not extend to the use of simulation lachrymal fluid, the available simulation dermal fluid data is nevertheless indicative of negligible bioavailability following exposure via the eyes. Since a chemical is required to be bioavailable in order to induce (non-mechanical) irritation, and since the substance has no pH <2 or >11, palladium dihydroxide is considered incapable of inducing eye corrosion. Therefore, and driven by the inconclusive in vitro data, the registrants consider it justified to not perform further in vivo mammalian testing but instead classify the substance as eye irritant cat 2 (H319).

 

No respiratory tract irritation data were identified. A new study was not conducted as it is not a REACH Standard Information Requirement. Further, palladium dihydroxide is not expected to reach the lungs in appreciable quantities (based on respiratory tract deposition modelling data - cf section 4.5). Thus, inhalation will not be a significant route of exposure.

 

Justification for classification or non-classification

Based on the results of the available in vitro skin irritation/corrosion studies with palladium dihydroxide and read-across test data from palladium monoxide, there is no requirement to classify palladium dihydroxide for skin irritation according to EU CLP criteria (EC 1272/2008).

 

Based on the results of the available in vitro eye irritation studies with palladium dihydroxide, combined with read-across test data from palladium monoxide, the low water solubility of palladium dihydroxide and the low dermal bioaccessibility of palladium dihydroxide, it was considered justified to classify palladium dihydroxide as eye irritant cat 2 (H319) according to EU CLP criteria (EC 1272/2008).