Registration Dossier

Environmental fate & pathways

Bioaccumulation: terrestrial

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Description of key information

As for aquatic bioaccumulation, this endpoint is not required for an Annex VII dossier. Based on the results of the water solubility experiment of erbium zirconium oxide, erbium and zirconium can be expected to be released to pore water only to an extremely limited content. Further, based on the data on zirconium bioconcentration in microalgae and cyanobacteria, it is clear that even when zirconium is added to the test medium as 'water soluble' test substance, bioavailability of zirconium for uptake is extremely low (due to transformation to and precipitation of insoluble zirconium substances at environmentally relevant pH levels). A similar behaviour is known for erbium. Erbium zirconium oxide is therefore assumed to have an extremely low potential for bioaccumulation in the terrestrial foodchain too. To support this assumption, the available literature data on terrestrial bioaccumulation of zirconium were added to this dossier. From the available study (Ferrand et al., 2006; Klimisch 2), it can be concluded that there is no concern for bioaccumulation of zirconium in terrestrial organisms, as all BSAF values (obtained for roots and aerial parts of plants) were well below 1. 

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Additional information

1. Information on zirconium

In the study of Ferrand et al. (2006), transfer of zirconium from soil to tomato and pea plants was studied during a 7-day exposure period in two soils (an acidic and a calcareous soil) amended with either a soluble (zirconium dichloride oxide or zirconium acetate) or an insoluble zirconium compound (Zr(OH)4, covered by the ZrO2 registration dossier). Zirconium accumulated mainly in the roots, with zirconium adsorption to the root surface being of minor relevance. Translocation to aerial parts was limited. BSAF values for roots were the highest for zirconium acetate and the lowest for Zr(OH)4. They were all <= 0.1. BSAF values for aerial parts were all <= 0.005 and were also generally the highest for zirconium acetate and the lowest for Zr(OH)4. These values are however all below 1, indicating that zirconium has a very limited potential for bioaccumulation in terrestrial organisms.

2. Information on erbium

It is not deemed necessary to add individual data on terrestrial bioaccumulation of erbium. Individual data on zirconium are considered sufficient for concluding on erbium zirconium oxide, because erbium bioavailability can reasonably be assumed to be similarly low as zirconium bioavailability after release of erbium zirconium oxide to the environment.

3. Conclusion on erbium zirconium oxide

Based on the available data on terrestrial bioaccumulation of zirconium, and taking into account the similar extremely low bioavailability of erbium and zirconium (extremely low water solubility of erbium zirconium oxide), and the similar environmental behaviour of erbium and zirconium (precipitation from solution at environmentally relevant pH levels), it can be concluded hat erbium zirconium oxide has no potential for terrestrial bioaccumulation of erbium or zirconium.