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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

BCF value taken into consideration for zirconium tetrachloride is the value estimated on the microalgae Chlorella emersonii exposed to a hydrated form of zirconium dichloride oxide. The BCF value is 0.64 L/kg dw.  

Key value for chemical safety assessment

BCF (aquatic species):
0.64 L/kg ww

Additional information

The hydrated form of zirconium dichloride oxide was the substance used to evaluate the accumulation of zirconium by the microalgal and cyanobacterial species. The test item was suitable as read-across substance for zirconium tetrachloride because ZrCl4 does not exist in the evironment as such due to rapid decomposition into ZrOCl2 + HCL. However, in water, ZrOCl2 is also an instable form of zirconium and will dissociate instantaneously into an hydrated form of ZrO2 (the most stable form in aqueous solution). In that context, value form these studies can be regarded as relevant for zirconium tetrachloride in solution.

Accumulation of zirconium by microalgae or cyanobacteria was due to a single phase metabolism-independent "biosorption" because values of Zr accumulation after 5 min or 4 hours were equivalent. Metal-ion binding to algal cell walls occurs partly through an ion-exchange mechanism, with binding sites arising from amino and carboxyl groups as well as sulphates and imidiazoles associated with polysaccharides and proteins in the cell wall. Biosorption is therefore highly dependent on cell wall structure and differences in amounts of Zr bound between the microalgal species is probably due to differences in the cell walls. For the studies presented in the present dossier, the biosorption of Zr was dependent on competing cations. Differences between organims may be attributed to (1) differences in cell wall structure, (2) different amounts of extracellular polysaccharide and (3) the result expressed in dry weight which does not take into account differences in the surface area available for Zr binding (Garnham et al., 1993). Overall, BCF values showed little to nor bioaccumalation in microalage and ranged between 0,1 - 0,6 L/kg dw.

Another publication of E. Ferrand studied the transfer of Zr from 2 type of soils (acidic and calcareous) to tomato and pea plants during 7 -days exposure. The 2 soils were amended with 3 forms of zirconium: ZrOCl2 or Zr acetate or Zr(OH)4. This study has also been regarded as suitable study for a read-across with zirconium tetrachloride (cf. above explanation). In the latter study, Zr was accumulated mainly in the roots, with Zr adsoption to the root surface being minor relevance. Translocation to aerial parts was limited. In that context, BSAF values for root were the highest for Zr acetate and the lowest for Zr(OH)4. They were all <= 0.1 BSAF values for aerial parts.