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EC number: 234-373-8 | CAS number: 11129-15-0
Bioaccumulation: aquatic / sediment
Administrative data
Link to relevant study record(s)
Description of key information
Because calcium zirconium oxide has a low water solubility, only small amounts of calcium and zirconium may become available for uptake when the substance is released to the environment. Experimental data for zirconium (key BCF of 0.064 L/kg ww for microalgae and cyanobacteria, Garnham et al., 1993) confirm that there is no concern for bioaccumulation of this element. For calcium, no data are available, however, calcium is an essential element and therefore internal calcium levels are actively regulated by organisms. Consequently, bioaccumulation of calcium would be very unlikely too. Based on the available information, it is concluded that there is no concern for bioaccumulation of zirconium or calcium released from calcium zirconium oxide.
Key value for chemical safety assessment
Additional information
1. Information on zirconium (dioxide)
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 of zirconium was very limited. BCF values between 0.0525 and 0.64 L/kg dw were obtained (element-based). Assuming 90% water content in the organisms, the highest value can be recalculated to a BCF of 0.064 L/kg ww. Since no bioconcentration/bioaccumulation data are available for zirconium for other groups of organisms, this BCF can be considered as the key BCF for zirconium.
2. Information on calcium (oxide)
In the aquatic environment and in soil, exposure to calcium oxide actually comes down to exposure to calcium and hydroxyl ions, with the formation of hydroxyl ions resulting in a pH increase (magnitude of pH-effect dependent on buffer capacity of the receiving system). However, both the intake of the essential element calcium and the internal pH (hydroxyl ions) of an organism are actively regulated (homeostasis) and therefore bioaccumulation is not considered a relevant endpoint for calcium.
3. Conclusion on calcium zirconium oxide
Calcium zirconium oxide has a low water solubility and only small amounts of calcium and zirconium will become available for uptake when the substance is released to the environment (see Eidam, 2014, 2015). For zirconium, experimental data confirm that there is no concern for bioaccumulation. For calcium, no data are available, but bioaccumulation is not considered a relevant endpoint because calcium is an essential element and internal calcium levels are actively regulated in organisms. Based on this information, it can be concluded that there is no concern for bioaccumulation of calcium or zirconium released from calcium zirconium oxide.
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