Zirconium iron pink zircon

Toxicity to microorganisms

Administrative data

Endpoint:

activated sludge respiration inhibition testing

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is highly insoluble in water, hence indicating that aquatic toxicity is unlikely to occur

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to Annex VIII, Column 2, Section 9.1.4. of Regulation (EC) 1907/2006, the test for activated sludge respiration inhibition does not need to be conducted “if there are mitigating factors indicating that aquatic toxicity is unlikely to occur, for instance if the substance is highly insoluble in water”.

Zirconium zircon with encapsulated hematite can be considered environmentally and biologically inert due to the characteristics of the synthetic process (calcination at a high temperature of approximately 1000°C), rendering the substance to be of a unique, stable crystalline structure in which all atoms are tightly bound and not prone to dissolution in environmental and physiological media. This assumption is supported by available transformation/dissolution data (Pardo Martinez, 2013) that indicate a very low release of pigment components. Transformation/dissolution tests at a loading of 100 mg/L for 7 days resulted in dissolved iron and zirconium concentrations below the LOD of < 0.5 µg/L at pH 6 and 2.4 µg Fe/L and 2.17 µg Zr/L at pH 8. Thus, metal release is maximised at pH 8. Transformation/dissolution at a loading of 1 mg/L and pH 8 resulted in dissolved iron and zirconium concentrations below the LOD (< 0.5 µg/L) after 7 and 28 days. Silicon was not considered in the T/D assessment since it does not have an ecotoxic potential as confirmed by the absence of respective ecotoxicity reference values in the Metals classification tool (MeClas) database (see also OECD 2004). Thus, the rate and extent to which Zirconium zircon with encapsulated hematite produces soluble (bio)available ionic and other iron- and zirconium-bearing species in environmental media is limited. Hence, the pigment can be considered as environmentally and biologically inert during short- and long-term exposure. The poor solubility of Zirconium zircon with encapsulated hematite is expected to determine its behaviour and fate in the environment, and subsequently its potential for ecotoxicity.

Proprietary studies are not available for Zirconium zircon with encapsulated hematite. The poorly soluble substance Zirconium zircon with encapsulated hematite is evaluated by comparing the dissolved metal ion levels resulting from the transformation/dissolution test after 7 and 28 days at a loading rate of 1 mg/L with the respective lowest acute and chronic ecotoxicity reference values (ERVs) as determined for the (soluble) metal ions. 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: An acute ERV for silicon has not been derived since a concern for short-term (acute) toxicity of silicon ions was not identified (see also OECD, 2004). The acute ERVs for iron (> 100 mg Fe/L) and zirconium (74 mg Zr/L) are above 1 mg/L and thus a concern for short-term (acute) toxicity was 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.” Due to the lack of an acute aquatic hazard potential for iron, silicon and zirconium ions and the fact that dissolved iron and zirconium concentrations remained below the LOD after 7 days at pH 8 and a loading of 1 mg/L in the T/D test, it can be concluded that the substance Zirconium zircon with encapsulated hematite is not sufficiently soluble to cause short-term toxicity at the level of the acute ERVs (expressed as EC50/LC50).

Regarding the long-term toxicity, a chronic ERV for silicon has not been derived since a concern for long-term (chronic) toxicity of silicon ions was also not identified (see also OECD, 2004). A chronic ERV has also not been derived for zirconium. For iron ions, the chronic ERV is above 1 mg/L and a concern for long-term (chronic) toxicity was not identified (no classification). According to ECHA Guidance on the Application of the CLP Criteria (Version 5.0, July 2017), ”Where the chronic ERV for the metal ions of concern corrected for the molecular weight of the compound (further called as chronic ERV compound) is greater than 1 mg/L, the metal compounds need not to be considered further in the classification scheme for long-term hazard.” Due to the lack of a chronic aquatic hazard potential for iron, silicon and zirconium ions and the fact that dissolved iron and zirconium concentrations were below the LOD of 0.5 µg/L after 28 days at pH 8 in the T/D test, it can be concluded that the substance Zirconium zircon with encapsulated hematite is not sufficiently soluble to cause long-term toxicity at the level of the chronic ERVs (expressed as NOEC/EC10).

In accordance with Figure IV.4 “Classification strategy for determining acute aquatic hazard for metal compounds” and Figure IV.5 „Classification strategy for determining long-term 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 hematite is poorly soluble and does not meet classification criteria for acute (short-term) and chronic (long-term) aquatic hazard.

Zirconium zircon with encapsulated hematite is poorly soluble. Based on the poor solubility and the corresponding lack of a toxic potential, inhibition of activated sludge respiration or toxicity to microorganisms is not expected. In accordance with Annex VIII, Column 2, Section 9.1.4. of Regulation (EC) 1907/2006, the test for activated sludge respiration inhibition is not necessary.

References:

OECD (2004) SIDS Initial Assessment Profile Silicon dioxide, Silicic acid, aluminum sodium salt, Silicic acid, calcium salt. SIAM 19, 19-22 October 2004.