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Read-across approach:

 

Zircon, cadmium yellow is a zircon-type oxide/pigment with the main structural element ZrSiO4 (Zr in an dodecahedral O environment) which forms a strong and inert matrix. Zr and Si are the main components with percentages of ~46% w/w and 15% w/w respectively. The amount of Cd as component is about 2% w/w.

 

The read-across substanceSilicic acid, zirconium salt, cadmium pigment encapsulated is a zircon-type pigment as well with an identical crystallographic structure and a very similar composition. Zr content is ~46% w/w and the Si content is ca. 14% w/w. Cd is present in about 4.7% w/w. Minor amounts of Se and S (1.53 and 1.04% w/w, respectively) are present as well.

 

Besides the obvious structural analogy the solubility of both pigments in aqueous and physilogical media are as follows (determination of Zr and Cd):

 

Solubility of Cd from the pigment Zircon, cadmium yellow in physiological media was in a range of 0.180µg/L (PBS) and 0.398 µg/L (ALF) after 2 hours. After 24 hours a dissolution range from 0.140 µg/L (GMB) - 0.722 µg/L (GST) was measured.

 

Solubility of Zr from the pigment Zircon, cadmium yellow in physiological media was in a range of below LODand 0.812 µg/L (ALF) after 2 hours. After 24 hours a dissolution range from below LOD (ASW) - 1.44 µg/L (ALF) was measured.

 

The read-across substance Silicic acid, zirconium salt, cadmium pigment encapsulated afforded after 2 hours a solubility for the element Cd in range of 0.07 µg/L (GMB) 2.58 µg/L (GST) and after 24 hours a solubility of 0.07 µg/L (GMB) to 6.13 µg/L (GST).

 

Solubility of Zr from the pigmentSilicic acid, zirconium salt, cadmium pigment encapsulatedin physiological media was in a range of below LODand 0.52 µg/L (ALF) after 2 hours. After 24 hours a dissolution range from below LOD - 1.25 µg/L (ALF) was measured.

 

T/D testing of the pigment Zircon, cadmium yellowafforded the following solubility at 1mg loading after 28 days:

Cadmium: below LOD (<0.0048) and 0.2077 ± 0.0993μg/L at pH 8 and pH 6, respectively

Zirconium: <LOD (0.0017μg/L) and 0.9241 ± 0.4349 at pH 8 and pH 6, respectively

 

T/D testing of the read-across substance Silicic acid, zirconium salt, cadmium pigment encapsulated afforded the following solubility at 1mg loading after 28 days:

Cadmium: 0.34 ± 0.09μg/L and 0.86 ± 0.39μg/L at pH 8 and pH 6, respectively

Zirconium: <LOQ (0.001μg/L) and <LOD at pH 8 and pH 6, respectively

 

In sum, the two zircon type pigments are structurally identical with very similar composition and both show a very low solubility in different artificial and aqueous media. In fact, the read-across substanceSilicic acid, zirconium salt, cadmium pigment encapsulated shows slightly higher dissolution and bioaccessibility without showing any signs of systemic or local toxicity in various studies (acute inhalation, skin/eye irritation, sensitisation). No toxicity on algae, fish and invertebrates could be observed in respective studies.

Hence, read-across to Silicic acid, zirconium salt, cadmium pigment encapsulated is fully justified.

Aquatic toxicity: freshwater, short-term

The table below presents an overview of the reliable acute aquatic toxicity data available for the hazard assessment of silicic acid, zirconium salt, cadmium pigment encapsulated.Concentrations are based on water accomodated fractions (WAF).

 

Pseudokirchneriella subcapitata

growth rate

72-h EC50

> 100 mg/L (WAF)

Wenzel, 2013

Daphnia magna

mortality 

48-h EC50 

6840 mg/L (WAF)

Weyand, 2000

Brachydanio rerio

mortality 

96-h LC50 

> 10000 mg/L (WAF)

Weyand, 2001

 

Invertebrates:The acute toxicity to Daphnia magna was determined according to OECD Guideline 202 (Weyand, 2000). Daphnids did not become immobilized during the test period of 48 h at tested concentrations up to 4000 mg/L (water accommodated fraction-WAF); the respective 48-h EC50 is 6840 mg/L (WAF).

 

Fish:Information on acute fish toxicity is available from a study performed according to OECD Guideline 203. Fish (Danio rerio) were exposed for 96 hours to water accommodated fractions up to 10000 mg/L under static conditions. At all tested loadings, neither behavioral abnormalities nor mortality occurred.

 

Algae:The toxic effects of the water accommodated fractions of silicic acid, zirconium salt, cadmium pigment encapsulated on the growth rate of algae (Pseudokirchneriella subcapitata) were studied in a state-of-the-art test according to OECD Guideline 201 (Wenzel, 2013). The EC50 value for the 72-h inhibition of growth rate of P. subcapitata is  > 100 mg/L (WAF).

 

Aquatic toxicity: freshwater, long-term

The table below presents an overview of the reliable long-term aquatic toxicity data available for the hazard assessment of silicic acid, zirconium salt, cadmium pigment encapsulated.Concentrations are based on water accomodated fractions.

 

Pseudokirchneriella subcapitata

growth rate

72-h EC10

> 100 mg/L (WAF)

Wenzel, 2013

 

Chronic toxicity data of silicic acid, zirconium salt, cadmium pigment encapsulated are available for algae. The long-term toxic effects of the Water Accommodated Fractions (WAF) of silicic acid, zirconium salt, cadmium pigment encapsulated on the growth rate of algae (Pseudokirchneriella subcapitata) were studied in a state-of-the-art test according to OECD Guideline 201 (Wenzel, 2013). The EC10 value for the 72-h inhibition of growth rate of P. subcapitata is  > 100 mg/L (WAF).

 

Acute aquatic toxicity data at three trophic levels (algae, daphnia, fish) and from standard toxicity tests indicate a lack of an acute toxic potential of silicic acid, zirconium salt, cadmium pigment encapsulated in the aquatic environment, i.e. all EC50 values are above 100 mg/L. Chronic toxicity data for algae indicate a lack of a toxicity potential of silicic acid, zirconium salt, cadmium pigment encapsulated in the aquatic environment long-term for this trophic level which may be explained at least in parts with the insolubility of the pigment.

 

Thus, based on available short-term and long-term aquatic toxicity data, classification and labelling for aquatic toxicity is not required in accordance with Directive 67/548 EEC and CLP Regulation (EC) No 1272/2008 (Table  4.1.0 (b) (iii)).