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No data is available on toxicity of diniobium pentaoxide to aquatic species.

In accordance with column 2 of Annex VII and VIII of Regulation (EC) No 1907/2006, short-term studies for the aquatic ecotoxicity do not need to be conducted if there are mitigating factors indicating that aquatic toxicity is unlikely to occur, for instance if the substance is highly insoluble in water. For diniobium pentaoxide a water solubility study has been performed resulting in a solubility <0.5 μg/L. An additionally performed oxide metal dissolution study came likewise to the result that the solubility is lower than 0.5 μg/L. Thus, diniobium pentaoxide is considered to be insoluble in water.

To prove whether a concentration of Diniobium pentaoxide lower than 0.5 μg/L, poses any potential risk to the aquatic environment, data from metals with a high toxicity to aquatic species can be considered for comparison. For example, Zinc is known to be very toxic to the aquatic environment (R50/53). For zinc a predicted no effect concentration (PNEC) of 7.8 μ/L was determined. This PNEC is still more than one order of magnitude above the water solubility of diniobium pentaoxide. Since this oxide cannot reasonably be considered to be more toxic than zinc, any adverse effect of diniobium pentaoxide can be excluded and testing is scientifically unjustified.

In column 2 of Annex IX of Regulation (EC) No 1907/2006, it is laid down that chronic toxicity tests shall be proposed by the registrant if the chemical safety assessment indicates the need to investigate further the effects on aquatic species. Since diniobium pentaoxide is not bioavailable, neither classified as dangerous to the environment nor it is a PBT or vPvB substance, there is no reason to perform long-term toxicity studies on aquatic species.

Diniobium pentaoxide is considered not to inhibit microorganisms in sewage treatment plants. Due to its insolubility in water the substance is assumed to be adsorbed and removed within the STP process.