Zirconium praseodymium yellow zircon

Toxicity to birds

Administrative data

Endpoint:

long-term toxicity to birds

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to Regulation (EC) 1907/2006, Annex X, Column 2, Section 9.6.1: “Any need for testing should be carefully considered taking into account the large mammalian dataset that is usually available at this tonnage level.”

According to the ECHA Guidance on information requirements and CSA (Chapter R.16: Environmental Exposure Estimation, Version: 2.1, October 2012), there is not a need for a detailed assessment of secondary poisoning i) if there are not any indications for bioaccumulation and ii) if there is not a potential for toxic effects if accumulated in higher organisms (based on classification on the basis of mammalian toxicity data).

Regarding mammalian toxicity and the relevant uptake via the oral pathway, signs of systemic toxicity were not observed in rats when administered at a dose of 1000 mg/kg bw/day for up to 28 days. Either no or only marginal increases in Pr plasma concentrations were observed, and only a minor fraction (<<0.001%) of the total administered dose of Pr was collected via urine, documenting the lack of bioavailability of this pigment (Leuschner, 2019). Thus, based on currently available information, the potential for systemic toxicity in mammals is low. According to the integrated testing strategy for avian toxicity in Figure R.7.10-2 of ECHA guidance on IR & CSA, R.7c (V 3.0, 2017), a mammalian hazard and risk cannot be identified. Thus, testing of zirconium praseodymium yellow zircon is not required.

According to ECHA guidance on IR & CSA, R.10 (2008); “Secondary poisoning is concerned with toxic effects in the higher members of the food chain, either living in the aquatic or terrestrial environment, which result from ingestion of organisms from lower trophic levels that contain accumulated substances. Previous cases have demonstrated that severe effects can arise after exposure of animals via their food and that bioconcentration, bioaccumulation and biomagnification in food chains need to be considered.”

Zirconium praseodymium yellow zircon 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 (Grane, 2010) that indicate a very low release of pigment components. Transformation/dissolution of zirconium praseodymium yellow zircon (24-screening test according to OECD Series 29, loading of 100 mg/L) resulted in mean dissolved praseodymium concentrations of 3.05 µg/L Pr and 21.66 µg/L Pr, silicon concentrations of 0.13 µg/L Si and 0.02 µg/L Si at pH 6 and 8, respectively, whereas dissolved zirconium concentrations remained below the LOD (< 0.08 µg/L Zr). Since silicon does not have an ecotoxic potential, as confirmed by the absence of respective ecotoxicity reference values in the Metals classification tool (MeClas) database, and the dissolution of praseodymium is highest at pH 6, pH 6 is considered as pH that maximised metal release. Metal release at the 1 mg/L loading and pH 6 resulted in dissolved concentrations of 2.10 µg/L Pr and 0.17 µg/L Zr after 7 days and 0.79 µg/L Pr and < 0.08 µg/L Zr (< LOD) after 28 days whereas silicon concentrations remained below the LOD (< 0.07 µg/L Si) during the test. Thus, the rate and extent to which zirconium praseodymium yellow zircon produces soluble (bio)available ionic and other praseodymium-, silicon- or 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 praseodymium yellow zircon is expected to determine its behaviour and fate in the environment, including its low potential for bioaccumulation and biomagnification.

Regarding the potential of bioaccumulation, the study of marine (seaweed, zooplankton, bivalves and fish) and terrestrial (Plants, fruits, liver of 15 wild avian and mammalian species) matrices by Squadrone et al. (2019) confirmed that rare earth elements, including praseodymium, “have a low potential for biomagnification, but instead are subject to trophic dilution”.

According to OECD (2004), “the bioavailable forms of silica (SiO2) are dissolved silica [Si(OH)4] almost all of which is of natural origin. The ocean contains a huge sink of silica and silicates where a variety of the marine habitat (diatoms, radiolarians, and sponges) is able to exploit this resource as a construction material to build up their skeletons”. Most organisms contain silicon at least at trace levels. Whereas silicon is essential for some organisms, including diatom algae, gastropods and mammals, and actively taken up, others take it up passively and excrete it.

“Due to the known inherent physico-chemical properties, absence of acute toxic effects as well as the ubiquitous presence of silica/silicates in the environment, there is no evidence of harmful long-term effects arising from exposure to synthetic amorphous silica/silicates (OECD, 2004).” Thus, given the ubiquitous presence of silica and silicates in the environment, silicon is regarded as element without or with a very low potential for bioconcentration and bioaccumulation.

Regarding the bioaccumulation potential of zirconium, Souza et al. (2020) evaluated abiotic and biotic matrices across six trophic levels (plankton, oyster, shrimp, mangrove trees, crabs and fish) in two neotropical mangrove estuarine ecosystems. Whereas biodilution of zirconium was observed at one location, a significant transfer was not be observed at the other. The lack of a potential for bioaccumulation may be explained (at least in part) with its very low solubility and mobility under most environmental conditions, mainly due to the stability of the principal host mineral zircon and the low solubility of the hydroxide Zr(OH)4 (Salminen et al. 2005).

Regarding essentiality, whereas praseodymium and zirconium are non-essential elements, having no known biological roles, silicon is considered necessary for various functions in some species, including diatom algae, gastropods and mammals. Silicon deficiency in animals may lead to delays in growth, bone deformations and abnormal skeletal development, and one of the symptoms of silicon deficiency is aberrant connective and bone tissue metabolism (Pérez-Granados and Vaquero, 2002).

Based on available information, there is not any indication of a bioaccumulation potential for zirconium praseodymium yellow zircon. In addition, the potential for systemic toxicity in birds and mammals is low. Hence, secondary poisoning is not considered relevant for zirconium praseodymium yellow zircon. In accordance with Regulation (EC) 1907/2006, Annex X, Column 2, Section 9.6.1, testing of zirconium praseodymium yellow zircon does not appear to be scientifically necessary and it is further scientifically not justified to conduct any toxicity study with birds for reasons of animal welfare.

References:

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

Pérez-Granados and Vaquero (2002) Silicon, aluminium, arsenic and lithium: Essentiality and human health implications. The Journal of Nutrition Health and Aging 6/2:154-62.

Salminen et al. (2005) Geochemical Atlas of Europe - Part 1: Background information, Methodology and Maps. EuroGeoSurveys.

Souza et al. (2020) Trophic transfer of emerging metallic contaminants in a neotropical mangrove ecosystem food web. Journal of hazardous materials 408: 124424.

Squadrone et al. (2019) Rare earth elements in marine and terrestrial matrices of Northwestern Italy: Implications for food safety and human health. Science of the Total Environment 660: 1383–1391.