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Studies investigating the acute toxicity of ytterbium oxide to fish (Ablitt, 2017) and daphnids (Noack, 2014) demonstrated that ytterbium oxide is not harmful to these organisms when exposing them to saturated solutions with a nominal loading rate equal to the limit test concentration for aquatic toxicity testing, i.e. 100 mg/L.

For algae, all available data for both water soluble, sparingly soluble, and insoluble rare earth 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 insoluble and sparingly soluble rare earth compounds, EC50 values (loading rate-based) were consistently > 100 mg/L (or > 100% v/v of a saturated solution with nominal loading rate 100 mg/L). Based on this information, ytterbium oxide can be concluded not to be harmful to algae either.

Finally, based on water solubility and exposure considerations, it is considered very unlikely that ytterbium oxide would be harmful to aquatic microorganisms and/or pose risks for adverse effects to occur in microorganisms in biological sewage treatment plants. Therefore, it was considered not necessary to perform an activated sludge respiration inhibition test with ytterbium oxide.

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