Zirconium zircon with encapsulated cadmium selenium sulphide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.19 µg/L

Assessment factor:

2

Extrapolation method:

sensitivity distribution

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

1.14 µg/L

Assessment factor:

2

Extrapolation method:

sensitivity distribution

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

20 µg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1.8 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.64 mg/kg sediment dw

Assessment factor:

1

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.9 mg/kg soil dw

Assessment factor:

1

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.16 mg/kg food

Assessment factor:

10

Additional information

Zirconium zircon with encapsulated cadmium selenium sulphide is moderately soluble in environmental media. Based on results of a standard transformation/dissolution test according to OECD Series 29, the dissolution at a loading of 1 mg/L Zirconium zircon with encapsulated cadmium selenium sulphide at pH 6, the pH that maximizes dissolution, results in dissolved cadmium levels of 0.41 µg Cd/L and 0.86 µg Cd/L and in dissolved selenium levels 0.05 µg Se/L and < LOQ (< 0.14 µg/L) after 7 and 28 days, respectively. At pH 8, dissolved cadmium levels amount to 0.18 µg Cd/L and 0.34 µg Cd/L and dissolved selenium levels to 0.05 µg Se/L and < LOQ (< 0.14 µg/L) after 7 and 28 days, respectively. Dissolved zirconium concentrations at a loading of 1 mg/L resulted in concentrations below the LOD (< 0.003 µg/L, pH 6 and 8) after 7 days, and below the LOD (< 0.001 µg/L, pH 6) or LOQ (< 0.002 µg/L, pH 8) after 28 days. Thus, the rate and magnitude to which Zirconium zircon with encapsulated cadmium selenium sulphide releases soluble, (bio)available ionic and other cadmium-, selenium- and zirconium-bearing species in environmental media is limited. Zirconium zircon with encapsulated cadmium selenium sulphide also contains silicon and sulfur, however, silicon (see OECD SIDS silicon dioxide, 2004) and sulfur do not have an ecotoxicological potential, as also confirmed by sulfate concentrations of the T/D media of 4.8 mg/L or 47.9 mg/L at pH 6 and 8 respectively and the absence of respective ecotoxicity reference values of silicon and sulfur in the Metals Classification tool (MeClas) database (http://www.meclas.eu accessed on 10.07.2021).

 

Further, the limited solubility of Zirconium zircon with encapsulated cadmium selenium sulphide is expected to determine its behaviour and fate in the environment, and subsequently its bioavailability and potential for bioaccumulation and ecotoxicity.

 

Since dissolved zirconium levels are below the respective LOD or LOQ and selenium levels are more than tenfold lower than the acute and chronic ERVs for selenium (i.e., 1.73 and 1.57 µg/L, respectively), the aquatic hazard potential of Zirconium zircon with encapsulated cadmium selenium sulphide is driven by the respective release of cadmium ions and thus assessed based on the cadmium release. A conservative read-across approach is applied based on all available information for various inorganic cadmium substances, and the fate of released cadmium ions can eventually be considered comparable to the general fate of cadmium ions in the environment. For further information on the applied read-across approach, please refer to the RAAF document “Read-across approach for the assessment of the environmental fate and toxicity of the pigment Zirconium zircon with encapsulated cadmium selenium sulphide” attached in IUCLID Section 13.

Conclusion on classification

Zirconium zircon with encapsulated cadmium selenium sulphide contains cadmium, selenium, zirconium, silicon and sulfur. Since silicon (see OECD SIDS silicon dioxide, 2004) and sulfur do not have an ecotoxicological potential, as also confirmed by sulfate concentrations of the T/D media of 4.8 mg/L or 47.9 mg/L at pH 6 and 8, respectively, and the absence of respective ecotoxicity reference values of silicon and sulfur in the Metals Classification tool (MeClas) database (http://www.meclas.eu accessed on 10.07.2021), the aquatic hazard potential of the substance Zirconium zircon with encapsulated cadmium selenium sulphide is evaluated by comparing the dissolved cadmium, selenium and zirconium levels resulting from the transformation/dissolution test at a loading rate of 1 mg/L at pH 6, the pH that maximises dissolution, with the lowest acute and chronic ecotoxicity reference values (ERVs) as determined for the (soluble) cadmium, selenium and zirconium ion.

The acute and chronic ERVs are based on the lowest EC50/LC50 and NOEC/EC10 values for algae, invertebrates and fish, respectively, and were obtained from the Metals classification tool (MeClas) database as follows:

Acute ERVs for silicon and sulfur have not been derived since a concern for short-term (acute) toxicity of silicon ions and sulfur was not identified. The acute ERV for zirconium (74 mg Zr/L) is above 1 mg/L and thus a concern for short-term (acute) toxicity was also not identified (no classification). According to ECHA’s Guidance on the Application of the CLP Criteria (Version 5.0, July 2017), “Where the acute ERV for the metal ions of concern is greater than 1 mg/L the metals need not be considered further in the classification scheme for acute hazard.” Furthermore, dissolved zirconium concentrations remained below the LOD after 7 days at pH 6 and 8 and a loading of 1 mg/L in the T/D test.

Acute ERVs for cadmium and selenium of 18 µg Cd/L and 1.73 µg Se/L (Selenastrum capricornutum) were obtained from the MeClas database. Dissolved cadmium and selenium levels of 0.41 µg Cd/L and 0.05 µg Se/L determined in the T/D test after 7 days at a loading of 1 mg/L and pH 6, i.e., the pH that maximises dissolution, are significantly (more than thirtyfold) lower than the corresponding short-term ERVs. Thus, the substance Zirconium zircon with encapsulated cadmium selenium sulphide is not sufficiently soluble to cause short-term toxicity at the level of the acute ERVs (expressed as EC50/LC50).In accordance with Figure IV.4 “Classification strategy for determining acute aquatic hazard for metal compounds” of ECHA Guidance on the Application of the CLP Criteria (Version 5.0, July 2017) and section 4.1.2.10.2. of Regulation (EC) No 1272/2008, the substance Zirconium zircon with encapsulated cadmium selenium sulphide is poorly soluble and does not meet classification criteria for acute (short-term) aquatic hazard. Applying the toxic-unit approach does also not result in any acute aquatic hazard identification. Further, these hazard conclusions are in accordance with classification conclusions of the Metals Classification tool (MeClas) database (http://www.meclas.eu accessed on 10.07.2021).

 

According to ECHA (2017b), “An ecotoxicity validation step may be important for alloys and complex metal containing materials (e.g. ores, concentrates, slags), where binding of the metal to abiotic and biological binding sites will in many cases be competitive. Therefore the ‘additivity mode’ is not necessarily valid and additional information may be relevant. Therefore, information from ecotoxicity validation steps could be useful in cases where a significant uncertainty is associated with the existing toxicity data. This ecotoxicity validation should have been derived from tests using most sensitive species at dissolved ion concentrations equivalent to those measured in the T/D medium. However, information from ecotoxicity testing directly in the T/D medium is not recommended because the composition of this medium is unlikely to meet the requirements for standard test media to ensure proper survival and/or reproduction. Therefore, ecotoxicity tests should have been conducted in standard media dosed at metal concentration equivalent to the concentration level actually measured in the T/D medium.” Further, according to the transformation/dissolution protocol (OECD Series No 29), “For hazard classification purposes the results of the dissolution/transformation protocol are compared with existing ecotoxicity data for metals and metal compounds. However, for purposes such as data validation, there might be cases where it may be appropriate to use the aqueous medium from a completed transformation test directly in an OECD 202 and 203 daphnia and fish ecotoxicity test. If the CaCl2.2H2O and MgSO4.7H2O concentrations of the transformation medium are reduced to one-fifth of the ISO 6341 medium, the completed transformation medium can also be used (upon the addition of micronutrients) in an OECD 201 algae ecotoxicity test.”

Accordingly, short-term ecotoxicity validation tests were performed with Zirconium zircon with encapsulated cadmium selenium sulphide for all three trophic levels, i.e. the toxicity of the dissolved fractions of individual loadings after 7 days (algae) and 24 h (invertebrates and fish) of dissolution of Zirconium zircon with encapsulated cadmium selenium sulphide was tested. Respective EC/LC50 values for the short-term toxicity to algae and fish are above 1000 and 10000 mg/L, respectively (Wenzel, 2013; Weyand, 2001), whereas the 48-h EC50 for the effect on aquatic invertebrate Daphnia magna amounts to 6840 mg/L (Weyand, 2000). Altogether, the aquatic toxicity data of Zirconium zircon with encapsulated cadmium selenium sulphide indicate that its potential for short-term (acute) toxicity is significantly lower than the acute aquatic toxicity of soluble cadmium and selenium salts. The EC50/LC50 values of Zirconium zircon with encapsulated cadmium selenium sulphide for all three trophic levels are above the classification criteria for short-term (acute) aquatic hazard. In accordance with Table 4.1.0 (a) of Regulation (EC) No 1272/2008, the substance Zirconium zircon with encapsulated cadmium selenium sulphide does also not meet classification criteria for short-term (acute) aquatic hazard.

 

Regarding the long-term toxicity, chronic ERVs for silicon and sulfur have not been derived since a concern for long-term (chronic) toxicity of silicon and sulfur was also not identified. A chronic ERV has also not been derived for zirconium.Chronic ERVs for cadmium and selenium of 0.21 µg Cd/L and 1.57 µg Se/L were obtained from the MeClas database.The dissolved cadmium concentration of 0.86 µg Cd/L in the T/D test after 28 days at pH 6, the pH that maximises dissolution, is above the long-term ERV of cadmium ions of 0.21 μg/L for aquatic invertebrates. Transformation/dissolution at a loading of 1 mg/L Zirconium zircon with encapsulated cadmium selenium sulphide results in dissolved selenium concentrations below the LOQ (< 0.14 µg/L) at pH 8 and pH 6, after 28 days in the T/D test, which are thus significantly (more than tenfold) below the chronic ERV for selenium ions (1.57 µg Se/L).Hence, the substance Zirconium zircon with encapsulated cadmium selenium sulphide may be considered sufficiently soluble to cause long-term toxicity at the level of the chronic ERV for cadmium ions. The cadmium ion satisfies the requirements for “rapid environmental transformation”, i.e. > 70% removal from the water column in 28 days and limited sediment remobilisation potential under most environmental conditions.

Based on the maximum cadmium content of 7.0 % for Zirconium zircon with encapsulated cadmium selenium sulphide, the ERV of cadmium ions can be recalculated for Zirconium zircon with encapsulated cadmium selenium sulphide resulting in an ERV of 3.0 µg/L. In accordance with Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008, the substance Zirconium zircon with encapsulated cadmium selenium sulphide would meet classification criteria for long-term (chronic) aquatic hazard Category 1.

For a more accurate refinement, the dissolution rate of Zirconium zircon with encapsulated cadmium selenium sulphide is taken into account, and the ERV for Zirconium zircon with encapsulated cadmium selenium sulphide is calculated from the chronic ERV of cadmium and the transformation/dissolution data of Zirconium zircon with encapsulated cadmium selenium sulphide obtained under the same circumstances as follows:

ERV(Pigment) = ERV (Cd++) * loading(Pigment) in T/D test / dissolved concentration (Cd+) measured after 28 d in T/D test, resulting in an ERV of 244.2 µg/L. In accordance with Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008, the substance Zirconium zircon with encapsulated cadmium selenium sulphide would meet classification criteria for long-term (chronic) aquatic hazard Category 3. As this calculation using the experimental transformation/dissolution data of Zirconium zircon with encapsulated cadmium selenium sulphide includes the actual amount of soluble, (bio)available ionic cadmium-containing species originating from Zirconium zircon with encapsulated cadmium selenium sulphide in environmental media, the ERV of 244.2 µg/L is considered more representative.

Therefore, the substance Zirconium zircon with encapsulated cadmium selenium sulphide is considered sufficiently soluble to cause long-term toxicity at the level of the chronic ERV for cadmium ions and in accordance with Table 4.1.0 (b) (ii) of Regulation (EC) No 1272/2008 meets classification criteria for long-term aquatic hazard Category 3. Applying the toxic-unit approach results in the same chronic aquatic hazard identification. Further, these hazard conclusions are in accordance with classification conclusions of the Metals Classification tool (MeClas) database (http://www.meclas.eu accessed on 10.07.2021).

In sum, the substance Zirconium zircon with encapsulated cadmium selenium sulphide is of limited solubility and does not meet classification criteria of Regulation (EC) No 1272/2008 for short-term (acute) aquatic hazard but meets classification criteria for long-term (chronic) aquatic hazard Category 3.