Registration Dossier
Registration Dossier
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EC number: 269-072-0 | CAS number: 68187-11-1 This substance is identified in the Colour Index by Colour Index Constitution Number, C.I. 77343.
Categories
- Category name:
- Cobalt chromite spinels
Justifications and discussions
- Category definition:
- Cobalt chromite spinels
- Category description:
- Cobalt chromite spinels
- Category rationale:
- Read-across category approach:
Cobalt chromite green spinel is a spinel-type oxide/pigment with the general structural element AB2O4 which forms a strong and inert matrix. Co and Cr are the main components with percentages of ~12.7% w/w and 44.3% w/w respectively. The amount of Zn as component is about 14.9% w/w.
The read-across substance Cobalt chromite blue green spinel is a spinel-type pigment as well with an identical crystallographic structure and a very similar composition. Co content is ~14.8% w/w and the Cr content is ca. 30% w/w. Al is present in about 9.4% w/w. Contents of Zn is about 15.1% w/w.
Besides the obvious structural analogy the solubility of both pigments in aqueous and physilogical media are as follows (determination of Co and Cr):
Solubility of Co from the pigment Cobalt chromite green spinel in physiological media was in a range of 17.2 µg/L (GMB) and 99.1 µg/L (ALF) after 2 hours. After 24 hours a dissolution range from 12.8 µg/L (GMB) - 108 µg/L (ALF) was measured.
Solubility of Cr from the pigment Cobalt chromite green spinel in physiological media was in a range of 0.264 µg/L (GMB) and 5.95 µg/L (GST) after 2 hours. After 24 hours a dissolution range from 0.452 µg/L (GMB) - 6.80 µg/L (GST) was measured.
The read-across substance Cobalt chromite blue green spinel afforded after 2 hours a solubility for the element Co in range of 0.34 µg/L (PBS) and 6.45 µg/L (ALF) and after 24 hours a solubility of 0.37 µg/L (GMB) to 9.89 µg/L (GST).
Solubility of Cr from the pigment Cobalt chromite blue green spinel in physiological media was in a range of below LOD and 1.11 µg/L (ALF) after 2 hours. After 24 hours a dissolution range from 0.18 µg/L (PBS) - 0.99 µg/L (ALF) was measured.
T/D testing of the pigment Cobalt chromite green spinel afforded the following solubility at 1mg loading after 28 days:
Cobalt: 2.038 ± 0.008 and 0.790 ± 0.039 μg/L at pH 8 and pH 6, respectively
Chromium: 1.489 ± 0.008 μg/L andZinc: 1.840 ± 0.378 μg/L and
T/D testing of the read-across substance Cobalt chromite blue green spinel afforded the following solubility at 1mg loading after 28 days:
Cobalt: below LOD at pH 8 and pH 6, respectively
Chromium: below LOD at pH 8 and pH 6, respectively
In sum, the two spinel type pigments are structurally identical with similar composition. Both show a very low solubility in different artificial and aqueous media. In fact, the read-across substance Cobalt chromite blue green spinel shows slightly lower dissolution and bioaccessibility without showing any signs of systemic or local toxicity in various studies (acute inhalation, skin/eye irritation, sensitisation).
Based on the information summarised above, read-across to Cobalt chromite blue green spinel is fully justified.
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