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Toxicological information

Skin sensitisation

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Administrative data

skin sensitisation: in vivo (LLNA)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010-04-26 to 2010-05-12
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 429 (Skin Sensitisation: Local Lymph Node Assay)
Version / remarks:
GLP compliance:
yes (incl. QA statement)
signed 2009-04-06
Type of study:
mouse local lymph node assay (LLNA)

Test material

Constituent 1
Chemical structure
Reference substance name:
Stearic acid, cobalt salt
EC Number:
EC Name:
Stearic acid, cobalt salt
Cas Number:
Molecular formula:
λ²-cobalt(2+) dioctadecanoate
Details on test material:
- Name of test material (as cited in study report): Cobalt Stearate (CoRC Study EFF18)
- Chemical name: octadecanoic acid, cobalt salt
- Physical state at room temperature: Solid pellets; violet colour
- Storage condition of test material: At room temperature, protected from light
- Volatile: No
- Water solubility at 37 °C: 0.48 g/L
- Stability in container after opening: Stable

No further information on the tets material was stated.

In vivo test system

Test animals

Details on test animals and environmental conditions:
- Source: Harlan Winkelmann, 33178 Borchen, Germany
- Age at study initiation: 8 - 9 weeks
- Weight at study initiation: 18 - 22 g
- Housing: Full barrier in an air-conditioned room; The animals were kept in groups of 5 animals in IVC cages, type II L, polysulphone cages on Altromin saw fibre bedding (lot no. 291109, preliminary test; 101109, main test)
- Diet (ad libitum): Altromin 1324 maintenance diet for rats and mice (lot no. 1130)
- Water (ad libitum): Tap water, sulphur acidified to a pH value of approx. 2.8 (drinking water, municipal resdue control, microbiological controls at regular intervals).
- Acclimation period: At least five days

- Temperature: 22 +/- 3°C
- Relative humidity: 55 +/- 10 %
- Air changes: At least 10 X / hour
- Photoperiod (hrs dark / hrs light): 12/12

No further information on the test animals was stated.

Study design: in vivo (LLNA)

other: acetone/olive oil (3+1 (v/v))
50 %, 25 % and 12.5 % of cobalt stearate (diluted in acetone/olive oil)
No. of animals per dose:
5 mice per test group
5 mice per negative control group (vehicle)
Details on study design:
Due to the solubility properties of the test item the vehicle acetone/olive oil was used. (Acetone, Prolabo, lot no. 09J140506, expiry date: 10/2013; olive oil highly refined, Sigma, lot no. 0001423657-22709119, expiry date: 05/2010)

- Compound solubility: Before the initiation of the preliminary test, a solubility test was performed to define the maximum concentration which is technically applicable to the animals. The maximum technically applicable concentration of the test item in the vehicle was found to be 50%.
To determined the highest tolerated and non-irritant test concentration a preliminary test was performed.
For this purpose, two animals were treated by topical application with the test item on three consecutive days at a concentration of 50 % (diluted in acetone/olive oil) to the entire dorsal surface of each ear.
One further animal was treated with 100 % acetone/olive oil and served as negative control.
From day 1 to day 4 the ear thickness of each animal was measured.
During this period also all clinical signs were recorded.
Cageside observations included spontaneous activity, lethargy, recumbent position, convulsions, tremors, apnoea, aspyxia, vocalisation, diarrhoea, changes in the skin and fur, eyes and mucous membranes (salivation, discharge).
No signs of systemic toxicity could be detected in any animal.
- Irritation: No signs of irritation at the application site could be detected in any animal.

Based on the results observed in the preliminary test the following test item concentrations were selected for the main study:
50 %, 25 % and 12.5 % (diluted in acetone/olive oil). The preparations were made immediately prior to each dosing.
Acetone/olive oil served as negative control.
Test regime:
- Topical application: Each mouse was treated by topical application of 25 µL of the selected solution to the entire dorsal surface of each ear.
Topical applications were performed once daily over three consecutive days.
-Administration of 3H-methyl thymidine ((TRK 300, 20 Ci/mmol; Perkin Elmer, lot no. 201003E), diluted to a working concentration of 80 µCi/mL):
Five days after the first topical application all mice were dosed with 20 µCi 3H-methyl thymidine by intravenous injection (tail vein) of 250 µL of 3H-methyl thymidine, diluted to a working concentration of 80 µCi/mL.
-Preparation of cell suspension:
Approximately 5 hours after 3H-methyl thymidine-injection all mice were sacrificed by cervical dislocation. The draining "auricular lymph nodes" were excised, individually pooled for each animal (2 lymph nodes per animal) and collected in phosphate buffered saline (PBS; BSL BIOSERVICE, lot no. PBS-22042010, expiry date:10/2010). A single cell suspension of pooled lymph node cells was prepared by gentle mechanical disaggregation through polyamide gauze (200 mesh size). After washing the gauze with PBS the cell suspension was pelleted in a centrifuge. The supernatant was discarded and the pellets were resuspended with PBS. This washing procedure was repeated.
After the final wash each pellet was resuspended in approx. 1 mL 5 % TCA (Trichloroacetic acid; Sigma, lot no. 105K0708, expiry date:11/2010) at approx. 4 °C for approximately 18 hours for precipitation of macromolecules. Each precipitate was once washed again, resuspended in 1 mL 5 % TCA and 7 mL scintillation fluid was added. Then this solution was transferred into scintillation vials and stored at room temperature overnight.
- Determination of incorporated 3H-methyl thymidine:
The 3H-methyl thymidine - incorporation was measured in a β-counter and expressed as the number of disintegrations per minute (DPM). Similarly, background 3H-methyl thymidine levels were also measured (5 % TCA). Determination of radioactivity was performed individually for each animal.

The proliferative response of lymph node cells was expressed as the number of radioactive disintegrations per minute per lymph node (DPM/NODE) and as the ratio of 3H-methyl thymidine - incorporation into lymph node cells of test group animals relative to that recorded for control group animals (STIMULATION INDEX). Before DPM/Node values were determined, background values were subtracted.
EC3 values, calculated concentrations which induce stimulation indices of three, are determined by linear interpolation {EC3 = c + [(3-d)/(b-d)] x (a-c)}, between two points of the stimulation indices axis, one above (a,b) and one below (c,d) the stimulation index of three. If all measured points are above or below the stimulation index of three, no EC3 value can be stated.
A substance is regarded as a 'sensitiser' in the LLNA if at least one concentration of the test item results in a 3 fold or greater increase in 3H-methyl thymidine - incorporation into lymph node cells of the lymph nodes of the test group animals, relative to that recorded for the lymph nodes of control group animals (Stimulation Index equal to or greater than 3.0).
No further information on the study design was stated.
Positive control substance(s):
other: P-Phenylenediamine (CAS 106-50-3, Sigma GmbH, purity > 98 %; Lot 128K0093; Vehicle: acetone/olive oil (3+1 (v/v acetone olive oil; 1 % concentration on 3 consecutive days)
Please see "Details on study design" above.

Results and discussion

Positive control results:
In the positive control group given P-Phenylenediamine at the concentration of 1 %, a stimulation index exceeding the threshold value of 3 (SI = 5.1) was noted. The study was therefore considered valid.

In vivo (LLNA)

Resultsopen allclose all
Test group / Remarks:
Test group / Remarks:
Test group / Remarks:
Cellular proliferation data / Observations:
12.5 %: 7546.0 (mean DPM); 3763.8 (mean DPM per node) 25 %: 13042.0 (mean DPM); 6511.8 (mean DPM per node) 50 %: 10832.0 (mean DPM); 5406.8 (mean DPM per node) Negative control: 1355.6 (mean DPM); 668.6 (mean DPM per node)

Any other information on results incl. tables

All animals survived throughout the test period without showing any clinical signs.

All animals showed the expected weight development, which includes a weight loss of up to 2 g throughout the study.

Applicant's summary and conclusion

Interpretation of results:
Category 1 (skin sensitising) based on GHS criteria
The test item cobalt stearate (CoRC Study EFF18) is expected to have sensitising properties and therefore, should be regarded as a dermal sensitiser.
According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item is classified as Category 1.