Zirconium iron pink zircon

Bioaccumulation: aquatic / sediment

Administrative data

Endpoint:

bioaccumulation in aquatic species: fish

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance has a low potential to cross biological membranes

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to Column 2 of Information Requirement 9.3.2., Annex IX, Commission Regulation (EU) 1907/2006, ”The study need not be conducted if: the substance has a low potential for bioaccumulation (for instance a log Kow ≤ 3) and/or a low potential to cross biological membranes.”

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, including its low potential for bioaccumulation.

Further, “for naturally occurring substances such as metals, bioaccumulation is more complex, and many processes are available to modulate both accumulation and potential toxic impact. Many biota for example, tend to regulate internal concentrations of metals through (1) active regulation, (2) storage, or (3) a combination of active regulation and storage over a wide range of environmental exposure conditions. Although these homeostatic control mechanisms have evolved largely for essential metals, it should be noted that non-essential metals are also often regulated to varying degrees because the mechanisms for regulating essential metals are not entirely metal-specific (ECHA, 2008).”

The potential essentiality and bioaccumulation of the pigment components iron, silicon and zirconium can be summarized as follows:

Iron as essential element plays a crucial role in a wide variety of biological process, i.e. electron transport, nitrogen fixation and oxidative metabolism. As an essential component of haemoglobin, it functions as a carrier of oxygen in the blood and muscles of animals. The uptake of iron into cells is actively regulated by a strict homeostatic control system. The active regulation of iron uptake in combination with internal detoxification mechanism indicates a low potential for iron bioaccumulation. This assumption is supported by results of Bustamante et al. (2000) indicating that iron concentrations of digestive glands of cephalopods living in natural and in iron-enriched habitats are similar. Winterbourn et al. (2000) further demonstrate that iron does not biomagnify but rather “biodilutes” up the aquatic food chain. Thus, the potential for bioaccumulation in aquatic environments can be expected to be low.

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. (2021) 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).

Thus, based on the poor solubility of Zirconium zircon with encapsulated hematite in aquatic environments, the potential of Zirconium zircon with encapsulated hematite for bioaccumulation can safely be expected to be low. Consequently, the study on bioaccumulation does not need to be conducted based on low solubility, bioavailability and a corresponding low bioaccumulation potential of Zirconium zircon with encapsulated hematite in accordance with Column 2 of Information Requirement 9.3.2., Annex IX, Commission Regulation (EU) 1907/2006.

References:

Bustamante et al. (2000) Bioaccumulation of 12 trace elements in the tissues of the nautilus Nautilus macromphalus from New Caledonia. Marine Pollution Bulletin 40/8: 688-696.

ECHA (2008) Guidance on IR & CSA, Appendix R.7.13-2: Environmental risk assessment for metals and metal compounds. July 2008.

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

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

Souza et al. (2021) Trophic transfer of emerging metallic contaminants in a neotropical mangrove ecosystem food web. Journal of hazardous materials 408: 124424.

Winterbourn et al. (2000) Aluminium and iron burdens of aquatic biota in New Zealand streams contaminated by acid mine drainage: effects of trophic level. The Science of The Total Environment 254, 45-54.