Zirconium

Endpoint summary

Additional information

In contact with moisture/water, Zirconium metal is directly oxidised and a relatively stable passivation layer of ZrO2 is formed at the surface. As ZrO2 is very poorly soluble (0.055 mg/L), the behaviour of Zr in water is driven by the solubilisation and complexation of ZrO2. Therefore, as for other Zirconium compounds, the relevant substances for read-across purpose that enables to characterize the effect of zirconium towards aquatic organisms is ZrO2 and any other Zirconium compounds leading to the formation of ZrO2 (ZrOCl2, ZrCl4). Therefore, most of the studies identified in this dossier are used for a read-across approach from these Zirconium compounds. Results are expressed both in terms of testing material and Zr. No ecotoxicological data was available for other Zirconium compounds.

For the 3 trophic levels (fish, invertebrates and algae) only acute studies are available.

Fish:

The selected key study for short-term acute toxicity was performed with zirconium dioxide (ZrO2) to Danio rerio exposed during 96 hours with a loading rate of 100 mg/L. The NOELR and LL50 recorded were > 100 mgZrO2/L i.e 74.03 mg Zr/L.

Another reliable study based on read across was carried out with zirconium tetrachloride (ZrCl4). The result displayed a pH-induced effect at a loading rate of 100 mg/L, due to the decomposition of ZrCl4 into HCl and ZrO2 and its hydrated forms in contact with water. The LC50 that could nevertheless be derived is > 20 mg Zr/L.

A last study was disregarded since the authors conduct this test as an additional toxicity study rather than a proper toxicity test to fish. Nevertheless, after weeks of exposure the result displayed no adverse effect at a loading rate of 100 mg ZrOCl2/L.

Invertebrates:

The identified key study is a GLP study performed with ZrO2 on Daphnia magna during 48 hours with 100 mgZrO2/L. No toxic effect was observed (NOEC – EC50: > 74.03 mg Zr/L).

The study performed with Zr metal is a supporting study in which Hyallela azteca were exposed in static condition for a period of 7 days. Small deviations of the OECD guideline were noted and LC50 > 1 mgZr/L was determined, which was the maximum loading concentration used in this study.

The second supportive study was on Tubifex tubifex exposed to Zirconium in a water only system. No effect was observed after 96 hours exposure (EC50 > 100 mgZr/L).   

Algae:

One reliable study was identified to assess short term toxicity to algae. The testing material used was Zirconium dichloride oxide (ZrOCl2). In this study, no toxic effect was attributed to zirconium and a NOEC value of > 102.5 mg Zr/L was determined in a test medium complemented with suitable amount of phosphate. Indeed, authors scientifically demonstrated that zirconium formed complex with phosphates inducing a phosphate depletion in the culture medium causing the stop in algal growth. But not toxic effect could be attributed to Zirconium.

The other identified study is on the algae Selenastrum capricornutum exposed to zirconium tetrachloride. A EC50 of 2.6 mg Zr/L was determined. The toxicity observed in this study was due to the pH drop caused by the decomposition of ZrCl4 into HCl in water, and could not be attributed to zirconium. As the materials and methods are not enough detailed, it was not possible to assess the validity of the study which was therefore disregarded for this reason.

Microorganisms:

No study was available in scientific database. A waiver was stated for the present endpoint due to the low water solubility of zirconium (< 0.05 mg/L) and its affinity to form complexes with ligands in water. Therefore, zirconium is not expected to be bioavailable to aquatic organisms. Furthermore, due to the nature of the substance (inorganic), no biological treatment is expected for this substance but in case a WWTP with several treatment steps exists on site, Zirconium will be removed in the primary settling tank and exposure of micro-organisms is unlikely.