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EC number: 238-694-4
CAS number: 14644-61-2
Following the read-across strategy, it is considered appropriate to cover this endpoint by a key study performed with zirconium dichloride oxide. This study (Garnham et al., 1993) was assigned a Klimisch score of 2 (reliable with restrictions). Bioconcentration factors were measured in cyanobacteria and microalgae and observed to be low. A key BCF value of 0.064 L/kg ww was selected as a worst case key value for use in case exposure calculations are needed for secondary poisoning (aquatic foodchain) or man via the environment.
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 key value.
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