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A reliable study investigating the acute toxicity of yttrium trinitrate to fish (Muckle, 2016) demonstrated that yttrium trinitrate is very toxic to fish, acutely.

To conclude on the acute toxicity of yttrium (trinitrate) to aquatic invertebrates, a lumped data set for yttrium trinitrate and yttrium trichloride (i.e. a similar water-soluble yttrium compound as yttrium trinitrate) was considered. Two reliable studies are available, one performed with yttrium trinitrate (Hefner, 2014) and another performed with yttrium trichloride (Ablitt, 2017). Based on the study performed with yttrium trichloride, which yielded the lowest yttrium-based EC50 value, yttrium trinitrate was concluded to be toxic to aquatic invertebrates, acutely.

For algae, all available data for both water-soluble, sparingly soluble, and insoluble rare earth compounds (including yttrium compounds) have been summarised and thoroughly evaluated in the document attached to IUCLID Section 13. In this expert statement, it is concluded that there is no scientific added value in the performance of further algal growth inhibition studies with rare earth compounds. For water-soluble compounds, the observed adverse effects on algal growth were always concurrent with phosphate depletion. So far, it has not convincingly been demonstrated that rare earths are capable of causing direct toxic effects in algae or aquatic plants. Moreover, the issue with the precipitation of phosphate from the test medium at test concentrations where the rare earth is in excess of the phosphate (and vice versa) cannot be technically overcome at this point in time. Since the phosphate depletion effect observed in the confined test systems is not considered to be relevant at an ecosystem level, and since NOEC and EC50 values obtained in algal growth inhibition experiments were never the driver for PNEC derivation or classification for the aquatic environment (instead, either fish or aquatic invertebrates were the driver for this), it was not considered useful to perform further algal growth inhibition experiments with rare earth compounds at this point in time.

Finally, based on a key read across study performed with yttrium trichloride (Bayliss, 2018), yttrium was concluded to be able to cause adverse effects on the respiration of activated sludge, however, due to the fact that no dissolved yttrium or phosphate concentrations were determined over the course of the study, it cannot be excluded that the observed adverse effects were concurrent with phosphate depletion from the test medium, and do not necessarily represent a direct toxic effect, as is the case in algal growth inhibition tests.

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