Zircon, cadmium yellow

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

19 October 2021 - 10 January 2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

REPORTING FORMAT FOR THE CATEGORY APPROACH
Zirconium zircon with encapsulated cadmium sulphide 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 substance Zirconium zircon with encapsulated cadmium selenium sulphide 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 Zirconium zircon with encapsulated cadmium sulphide in physiological media was in a range of 0.180 µg/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 Zirconium zircon with encapsulated cadmium sulphide in physiological media was in a range of below LOD and 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 Zirconium zircon with encapsulated cadmium selenium sulphide 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 pigment Zirconium zircon with encapsulated cadmium selenium sulphide in physiological media was in a range of below LOD and 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 Zirconium zircon with encapsulated cadmium sulphide afforded 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:
T/D testing of the read-across substance Zirconium zircon with encapsulated cadmium selenium sulphide afforded the following solubility at 1mg loading after 28 days:
Cadmium: 0.34 ± 0.09 μg/L and 0.86 ± 0.39 μg/L at pH 8 and pH 6, respectively
Zirconium:
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 substance Zirconium zircon with encapsulated cadmium selenium sulphide shows slightly higher dissolution and bioaccessibility without showing any signs of systemic or local toxicity in various studies (acute oral and inhalation, skin/eye irritation, sensitisation, mutagenicity and 28d oral repeated dose toxicity).
Hence, read-across to Zirconium zircon with encapsulated cadmium selenium sulphide is fully justified.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2022

Report date:

2022

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Version / remarks:

corrected June 26, 2020

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)

Version / remarks:

dated May 30, 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

GLP certificate signed on 23 Oktober 2019

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1