Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

In contact with water, Zirconium tetrachloride decomposes instantaneously into HCl and ZrOCl2. Then, ZrOCl2 is also not stable in water and hydrolyses rapidly and precipitates into Zirconium dioxide and Hydrochloric acid, under environmental conditions. As HCl is not toxic to aquatic organisms (only pH effect), it will not be considered as a relevant degradation product to assess ZrCl4 toxicity. Therefore, as for other Zirconium compounds, the relevant degradation product to characterize the effect of zirconium tetrachloride for the aquatic toxicity is ZrO2 (or indirectly ZrOCl2). Therefore, most of the studies identified in this dossier are used for a read-across approach from Zirconium compounds leading to the formation of ZrO2 or its hydrated forms in water. Results are expressed both in terms of testing material and ZrCl4. 

For the 3 trophic levels (fish, algae and invertebrates) 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 190 mg ZrCl4/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 > 51 mg ZrCl4/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 onDaphnia magnaduring 48 hours with 100 mgZrO2/L. No toxic effect was observed (NOEC – EC50: > 190 mg ZrCl4/L).

A supporting study performed on Tubifex tubifex exposed to ZrOCl2 in a water only system has been reported. No effect was observed after 96 hours exposure (EC50 > 100 mgZr/L i.e EC50> 255 mgZrCl4/L).   

Another supporting study on Hyallela azteca exposed to Zr metal in static conditions for a period of 7 days has been identified. Small deviations of the OECD guideline were noted and LC50 > 1 mgZr/L i.e LC50> 255 mgZrCl4/L was determined, which was the maximum loading concentration used in this study.

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 > 262 mg ZrCl4/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 ZrCl4. A EC50 of 2.6 mg Zr/L was determined (i.e 6.64 mgZrCl4/L). 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.

Microorganism:

No study was available in scientific database. Due to the behaviour of ZrCl4 in water, a waiver was proposed for the present endpoint due to the low water solubility of ZrO2 (0.055 mg/L) and its affinity to form complexes with ligands in water. Therefore, ZrO2 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, Zr compounds will be removed in the primary settling tank and exposure of micro-organisms is unlikely.