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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

Because erbium zirconium oxide as well as its individual 'components' in the solid solution erbium oxide and zirconium dioxide have an extremely low water solubility, it is anticipated that erbium zirconium oxide has no potential for bioconcentration and bioaccumulation. Although this endpoint (REACH Annex IX) is not required for this Annex VII dossier, the available literature data on bioconcentration/bioaccumulation of zirconium are included in this dossier to confirm this statement. The experiments by Garnham et al. (1993) on bioconcentration of zirconium in cyanobacteria and microalgae were performed using zirconium dichloride oxide, a 'water soluble' zirconium substance. Therefore the results from these tests represent conservative information on bioconcentration of zirconium compared to when an insoluble substance such as zirconium dioxide would have been used. This key study reported very low bioconcentration factors. A key BCF value of 0.064 L/kg ww was selected as a worst case key value. This value indicates that zirconium has an extremely low potential for bioconcentration/bioaccumulation.

Key value for chemical safety assessment

Additional information

1. Information on zirconium

The accumulation of zirconium by cyanobacteria and microalgae was characterized by Garnham et al. (1993). In this study the organisms were exposed to solutions of zirconium dichloride oxide. Actual exposure however was rather to zirconium dioxide, since zirconium dichloride oxide hydrolyses rapidly in aqueous solutions at environmentally relevant pH, resulting in the precipitation of zirconium as zirconium dioxide or hydroxide. In all cyanobacterial and microalgal species examined, accumulation consisted of a single rapid energy-independent phase ("biosorption"). No energy-dependent accumulation was observed. Biosorption of zirconium was concentration-dependent, followed a Freundlich adsorption isotherm, and was dependent on pH, showing decreasing accumulation with decreasing pH. Zirconium desorption from micro-algae and cyanobacteria was increased by increasing external cation concentrations or by decreasing the pH of the desorption agent. Overall, biosorption/bioaccumulation was very limited. BCF values between 0.0525 and 0.64 L/kg dw were obtained. Assuming 90% water content in the organisms, the highest value can be recalculated to a BCF of 0.064 L/kg ww. This highest value can be considered as a key value for zirconium.

2. Information on erbium

Based on the low water solubility of erbium oxide the bioconcentration/bioaccumulation of erbium is anticipated to be extremely low. It was not considered necessary to add experimental data to the dossier.

3. Conclusion on erbium zirconium oxide

Based on the low water solubility of erbium zirconium oxide as well as the individual components of the solid solution (zirconium dioxide and erbium oxide), bioconcentration/bioaccumulation of erbium and zirconium from erbium zirconium oxide is anticipated to be extremely low. This is confirmed in this dossier by the available literature data on bioconcentration of zirconium in microalgae and cyanobacteria (Garnham et al., 1993). Based on the key study for zirconium dioxide (read across from zirconium dichloride oxide), it can be concluded that there is no concern for bioconcentration/bioaccumulation of zirconium.