Zirconium tetrachloride

Toxicity to aquatic algae and cyanobacteria

Description of key information

Considering the 2 studies identified for toxicity to aquatic algae and cyanobacteria, key study on Chlorella vulgaris displays no effect on growth with a NOEC value of 262 mg ZrCl4/L. However, zirconium induces systematically a precipitation of the posphate in the medium leading to a direct impact on growth of the algae. Therefore, by adding suitable amount of phosphate in the medium of alage exposed to Zr, the growth of algae was restored.

Key value for chemical safety assessment

EC50 for freshwater algae:

262 mg/L

Additional information

Two studies have been identified to assess the toxicity to aquatic algae based on read-across susbtances for zirconium tetrachloride. The key study identified had exposed Chlorella vulgaris to zirconium dichloride oxide (ZrOCl2). ZrOCl2 is a suitable compound for zirconium tetrachloride read-across. Indeed, ZrCl4 does not exist in the environment because in water, it decomposes instantaneously into HCl and ZrOCl2. Then, ZrOCl2 is also not stable in water and hydrolises rapidly and precipitates into Zirconium dioxide. Therefore, once the pH neutralized, zirconium dioxide is the substance tested due to the particular physico-chemical properties of the zirconium tetrachloride.Chlorella vulgaris was not impacted by zirconium showing a NOEC of 200 mg ZrOCl2/L i.e 262 mg ZrCl4/L. These conclusions are valide only if the medium is supplemented with phosphate. Actually, Kumar at al. (1978) experimentally proved that the toxic effect observed on growth algae was due to the lack of phosphate which is precipitated by the zirconium in the growth medium. Therefore, by adding suitable amount of phosphate, growth of the algae could be restored with no toxic effect induced by zirconium. The other disregarded study (Couture et al. (1989) shows an effect with an EC50 of 6.64 mg ZrCl4/L. However, the authors mentioned that the observed effect was also due to phosphate-induced toxic effect (depletion) instead of a direct toxicity effect of zirconium on algae growth. However, as this study does not enable to derive a suitable EC50, it has been disregarded. There is no available study to assess the toxicity to algae of ZrO2 alone.Indeed, another study using reaction mass of a lanthanide element and zirconium dioxide displayed no toxic effect. However, since the testing material used is not the zirconium dioxide pure, results have not been considered for the present dossier.