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The maximum water solubility of Ta2O5 was determined according to the OECD Guideline 105.  Test solutions were stirred up to 5 days at 10 °C and 20 °C, loading: 50 mg/L. Solubility measurements were conducted daily. The water solubility of the test substance was determined to be < 5 µg/L for all time points (see Wenighöfer & Fröschl, 2012). Thus, it can be concluded that Ta2O5 is highly insoluble in water. Therefore, aquatic toxicity is unlikely to occur.

This is confirmed by the acute aquatic toxicity studies conducted with fish, daphnia and algae (see Caspers, 2000 & 2001; Müller, 2001). In each test, the test substance was applied at a nominal concentration of 1 mg/L. Test media were prepared by direct addition of Ta2O5 to the dilution water, ultrasonication (1 h), stirring (24 h) and filtration of any undissolved particles.

Due to the procedures for the preparation of the test solutions, it can be assumed that the maximum dissolved Ta2O5 concentration was achieved in the test solutions.

Typically, the dissolved concentration of a test substance in these test media is lower than in OECD 105 tests. Thus, it can be concluded that the saturation concentration in the aquatic toxicity tests were < 5 µg/L.

No toxic effects could be observed in any of the acute aquatic toxicity tests at saturation. In addition, Ta2O5 does not meet the criteria for classification as dangerous according to Regulation (EC) No 1272/2008 or is assessed to be a PBT or vPvB. The hazard assessment reveals neither a need to classify the substance as dangerous to the environment, nor that it is a PBT or vPvB substance. In accordance with Column 2 of REACH Annex IX, endpoints 9.1.5 & 9.1.6, testing proposals for a long-term aquatic toxicity do not need to be provided.  

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