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Administrative data

Endpoint:
skin corrosion: in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2016-08-08 to 2016-10-13
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2016
Report date:
2016

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 431 (In Vitro Skin Corrosion: Reconstructed Human Epidermis (RHE) Test Method)
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Chemical structure
Reference substance name:
Tungsten hexachloride
EC Number:
236-293-9
EC Name:
Tungsten hexachloride
Cas Number:
13283-01-7
Molecular formula:
Cl6W
IUPAC Name:
tungsten hexachloride
Test material form:
solid
Details on test material:
- Batch No.: 151001
- Specification: undergoes hydrolysis
- Colour: dark violet
- Density: 3.52 g/cm3
- Purity: > 99.9%
- Expiry Date: July 2018
- Storage Conditions: cool and dry under air exclusion

In vitro test system

Test system:
human skin model
Source species:
human
Cell type:
non-transformed keratinocytes
Cell source:
skin obtained from plastic surgery from multiple donors
Justification for test system used:
This test uses the EPISKIN-SM™ reconstructed human epidermis model (SkinEthic) which consists of normal human epidermal keratinocytes (NHEK) and therefore represents in vitro the target organ of the species of interest and closely mimics the biochemical and physiological properties of the upper parts of the human skin, i.e. the epidermis.
Vehicle:
unchanged (no vehicle)
Details on test system:
RECONSTRUCTED HUMAN EPIDERMIS (RHE) TISSUE
- Model used: EPISKIN-SM^TM
- Tissue batch number(s): Lot: 16-EKIN-034

TEMPERATURE USED FOR TEST SYSTEM
- Temperature used during treatment / exposure: room tempertaure
- Temperature of post-treatment incubation (if applicable): MTT assay plate incubated at 37 °C

REMOVAL OF TEST MATERIAL AND CONTROLS
- Volume and number of washing steps: using a wash bottle the tissue was gently rinsed about 15 times with 25 mL PBS to remove any residual test item

MTT DYE USED TO MEASURE TISSUE VIABILITY AFTER TREATMENT / EXPOSURE
- MTT concentration: MTT assay plate containing 2 mL pre-warmed MTT solution (final concentration: 0.3 mg/mL)
- Incubation time: 3 h +/- 15 min
- Spectrophotometer: plate spectrophotometer
- Wavelength: 570 nm
- Filter bandwidth: filter band pass of maximum +/-30 nm

NUMBER OF REPLICATE TISSUES: two replicates for each treatment period (3 min, 60 min and 4h exposure) for the negative control and test item group. For the positive control the test was performed with two replicates for the 4 h exposure.

CONTROL TISSUES USED IN CASE OF MTT DIRECT INTERFERENCE
- killed tissues
- N. of replicates : two tissues per treatment period were treated with the test item (KT) and with 0.9% NaCl (KU).
- Method of calculation used: NSMTT was calculated relative to the negative control of living tissues (NK) per treatment period according to the following formula: NSMTT= [(OKkt - ODku)/ODnk]*100

PREDICTION MODEL / DECISION CRITERIA:
A test item is classified as non-corrosive if relative tissue viability after 4 h treatment is not decreased to less than 35% of the corresponding negative control tissues. A test item is classified corrosive (C, in accordance with UN GHS category 1) in any case, if the relative tissue viability after 4 h treatment is decreased below 35%: if viability is reduced to less than 35% after 4 h treatment and to more than 35% after 60 min treatment or to less than 35% viability after 60 min but not more than 35% after 3 min treatment, the test item is classified as corrosive, in accordance with optional UN GHS sub-categories 1B and 1C. A test item which decreases viability below 35% after 3 min treatment is classifed as corrosive in accordance with optional UN GHS sub-category 1A.
Control samples:
yes, concurrent negative control
yes, concurrent positive control
yes, concurrent MTT non-specific colour control
Amount/concentration applied:
TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 20 ± 2 mg of the test substance was applied directly atop the EPISKIN SM^TM tissue. Due to instability of the test item in presence of water and therefore related to technically feasibility, the test item was not moistened with 100 µL physiological saline.

NEGATIVE CONTROL
- Amount(s) applied (volume or weight): 50 µL 0.9% NaCl (physiological saline; CAS No.: 7647-14-5; Lot 151418071, B. Braun Melsungen)

POSITIVE CONTROL
- Amount(s) applied (volume or weight): 50 µL Glacial acetic acid (CAS No.: 64-19-7; Lot K47336863548, Merck)
Duration of treatment / exposure:
3 min, 60 min and 4 h
Number of replicates:
2 tissues per dose group and time point

Results and discussion

In vitro

Resultsopen allclose all
Irritation / corrosion parameter:
% tissue viability
Run / experiment:
3 min
Value:
86
Negative controls validity:
valid
Positive controls validity:
valid
Irritation / corrosion parameter:
% tissue viability
Run / experiment:
60 min
Value:
2
Negative controls validity:
valid
Positive controls validity:
valid
Irritation / corrosion parameter:
% tissue viability
Run / experiment:
4 h
Value:
2
Negative controls validity:
valid
Positive controls validity:
valid
Other effects / acceptance of results:
For detailed results please see "Any other information on results"

Any other information on results incl. tables

Results of the Pre-Experiment

The mixture of 20 mg test item per 2 mL MTT medium showed reduction of MTT as compared to the solvent. The mixture turned blue/purple.

For quantitative correction of results, the part of absorption due to the non-specific reduction of MTT (NSMTT) was determined by using killed tissues. Therefore, two tissues per treatment period were treated with the test item (KT) and with 0.9% NaCl; KU, respectively. NSMTT was calculated relative to the negative control of living tissues (NK) per treatment period according to the following formula:

NSMTT = [(ODKT- ODKU)/ODNK] * 100

NSMTT was ≤ 50% relative to the negative control of living epidermis after all three treatment periods: in the 3 min experiment NSMTT was 3.4%, in the 60 min experiment 1.6%, in the 4 h experiment 1.9%. This means that the test item was washed away almost completely before the addition of the MTT solution. The true MTT metabolic conversion (TODTT) of the test item treated living tissues (TM) was corrected for each treatment period according to the following formula:

TODTT= ODTM- (ODKT- ODKU).

The mixture of 10 mg test item per 90 µL Aqua. dest. showed no colouring as compared to the solvent.

The mixture of 10 mg test item per 90 µL isopropanol showed colouring as compared to the solvent and absorbs light in the range of 570 ± 30 nm. Therefore, the tissue staining potential of the test item was checked by treatment of two additional viable tissues per treatment period with the test item (TVT) and one additional tissue for the negative control (UVT). For quantitative correction of results, the part of absorption due to the non-specific colour (NSCliving) was determined by using MTT-free assay medium for staining according to the following formula:

NSCliving[%] = [ODTVT/ODUVT]* 100.

NSClivingwas ≤ 5% relative to the negative control of living epidermis after all three treatment periods: in the 3 min experiment NSC was 1.3%, in the 60 min experiment 1.3%, in the 4 h experiment 2.1%. Therefore, no correction of the results was necessary.

Results of the main experiment

Table 2: Blank values

Name  Blank (viable tissues)
Absolute OD570
(raw data)
0.042
0.042
0.042
0.042
0.042
0.042
Mean OD 570
(mean of two alliquots per tissue)
0.042

Table 3: 3 min Experiment

Name Negative Control Test Item
Tissue 1 2 1 2
Absolute OD570
(raw data)
0.852
0.877
0.878
0.923
0.811
0.817
0.761
0.793
Mean OD 570
(mean of two alliquots per tissue)
0.864 0.900 0.814 0.777
Mean OD570 (Blank corrected 0.822 0.858 0.772 0.735
Total Mean OD570 of 2 Replicate Tissues (Blank corrected) 0.840* 0.753
TODTT - 0.725
Relative Tissue Viabilities [%] 97.8 102.2 91.9 87.5
Mean Relative Tissue Viabilities [%] 100 90
MSMTT-corrected mean relative tissue viability [%] - 86
differecne of relative tissue viability [%]*** 4.3 4.4

* corrected mean OD570 of the negative control corresponds to 100 % absolute tissue viability.

*** difference between each two replicates is ≤ 30 % (in the range of 20 - 100 % viability and for ODs > 0.3)

Table 4: 60 min Experiment

Name Negative Control Test Item
Tissue 1 2 1 2
Absolute OD570
(raw data)
0.842
0.843
0.928
0.960
0.064
0.066
0.079
0.078
Mean OD 570
(mean of two alliquots per tissue)
0.842 0.944 0.065 0.078
Mean OD570 (Blank corrected 0.8 0.902 0.023 0.036
Total Mean OD570 of 2 Replicate Tissues (Blank corrected) 0.851* 0.03
TODTT - 0.016
Relative Tissue Viabilities [%] 94 106 2.7 4.3
Mean Relative Tissue Viabilities [%] 100 3
MSMTT-corrected mean relative tissue viability [%] - 2
differecne of relative tissue viability [%]*** 11.9 1.6

* corrected mean OD570 of the negative control corresponds to 100 % absolute tissue viability.

*** difference between each two replicates is≤ 30 % (in the range of 20 - 100 % viability and for ODs > 0.3)

Table 5: 4 h Experiment

Name Negative Control Test Item Positive Control
Tissue 1 2 1 2 1 2
Absolute OD570
(raw data)
0.923
0.960
0.853
0.897
0.079
0.091
0.064
0.066
0.071
0.062
0.082
0.079
Mean OD 570
(mean of two alliquots per tissue)
0.942 0.875 0.085 0.065 0.067 0.080
Mean OD570 (Blank corrected 0.900 0.832 0.043 0.023 0.025 0.038
Total Mean OD570 of 2 Replicate Tissues (Blank corrected) 0.866* 0.033 0.031
TODTT - 0.016 -
Relative Tissue Viabilities [%] 103.9 96.1 4.9 2.6 2.8 4.4
Mean Relative Tissue Viabilities [%] 100 4 4**
MSMTT-corrected mean relative tissue viability [%] - 2 -
differecne of relative tissue viability [%]*** 7.8 2.3 1.6

* corrected mean OD570 of the negative control corresponds to 100 % absolute tissue viability.

** mean relative tissue viability of the two positive of the 4 h treatment period is ≤ 20 %.

*** difference between each two replicates is ≤ 30 % (in the range of 20 - 100 % viability and for ODs > 0.3)

Applicant's summary and conclusion

Interpretation of results:
Category 1B (corrosive) based on GHS criteria
Conclusions:
Under the given conditions the test item Tungsten hexachloride showed corrosive effects. It is therefore classified as corrosive in accordance with a combination of optional UN GHS sub-categories 1B and 1C.
Executive summary:

In the present study the skin corrosion potential of Tungsten hexachloride (>99.9 % purity) was analysed according to OECD 431 using the EPISKIN-Standard Model™ (EPISKIN-SMTM), a reconstituted three-dimensional human epidermis model to distinguish between UN GHS “Category 1A" and "Category 1B/C” skin corrosive test substances and non-corrosive substances. Hereby, the test item was applied topically. Cytotoxicity is expressed as the reduction of mitochondrial dehydrogenase activity measured by formazan production from MTT after 3 min, 60 min and 4 h exposure and compared to those of the concurrent negative controls.

In this study under the given conditions the test item showed corrosive effects (86.0 % (3 min), 2 % (60 min and 4 h) mean relative tissue viability). The relative mean tissue viability after 60 min was reduced to less than 35% but not more than 35% after 3 min treatment. The test item Tungsten hexachloride is therefore classified as corrosive in accordance with a combination of optional UN GHS sub-categories 1B and 1C.

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