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Description of key information

Ytterbium trinitrate is registered as an intermediate under strictly controlled conditions for a tonnage inferior to 100 t/y. Therefore, the data requirement is to submit the available existing information. Rather than concluding on the sole basis of the available data on Danio rerio and Carassius auratus (see IUCLID sections 6.1.1 and 6.1.2) and Hyalella azteca (see IUCLID section 6.1.3), it was preferred to follow a weight-of-evidence approach and to consider all the data available on the rare earth trinitrates family in order to apply a worst-case classification as a matter of precaution. As it can be evidenced from rare earth trinitrates that have been already tested, these ones are:

 

- Toxic to very toxic fish:

    > Lanthanum trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 1.01 mg/L (Klimisch 1, key study)

    > Cerium trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 0.3 mg/L (Klimisch 1, key study)

    > Praseodymium trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 0.71 mg/L (Klimisch 3, supporting study*)

    > Neodymium trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 2 mg/L (Klimisch 3, supporting study*)

    > Gadolinium trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 0.93 mg/L (Klimisch 3, supporting study*)

    > Dysprosium trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 2 mg/L (Klimisch 3, supporting study*)

    > Yttrium trinitrate: 96h-LC50 (Oncorhynchus mykiss) = 0.62 mg/L (Klimisch 1, key study) and 96h-LC50 (Oncorhynchus mykiss) = 2.3 mg/L (Klimisch 3, supporting study*)

 

N.B. Studies on praseodymium, neodymium, praseodymium, gadolinium, dysprosium and yttrium trinitrates legended with * did not include any analytical monitoring to investigate the stability of the test items in the test media. Precipitation of rare earths may have occurred; which could have led to an underestimation of the ecotoxicity. Therefore, the results should not be considered entirely reliable. However, as relatively important adverse effects were observed in these studies underestimating toxicity, they may be used as supporting studies.

 

- Harmful to toxic to daphnids:

    > Lanthanum trinitrate: 48h-EC50 (Daphnia magna) = 3 mg/L (Klimisch 1, weight-of-evidence)

    > Cerium trinitrate: 48h-EC50 (Daphnia magna) = 16 mg/L (Klimisch 1, key study)

    > Praseodymium trinitrate: 48h-EC50 (Daphnia magna) = 2 mg/L (Klimisch 1, key study)

    > Neodymium trinitrate: 48h-EC50 (Daphnia magna) = 8.1 mg/L (Klimisch 1, key study)

    > Gadolinium trinitrate: 48h-EC50 (Daphnia magna) = 2.9 mg/L (Klimisch 1, key study)

    > Yttrium trinitrate: 48h-EC50 (Daphnia magna) = 11.5 mg/L (Klimisch 1, key study)

 

Considering this pool of data, it was decided to apply the worst-case conclusion to ytterbium trinitrate and to consider it as very toxic to aquatic life. In spite of its Klimisch score of 3, the available data on Hyalella azteca (see IUCLID section 6.1.3) goes in the same direction by concluding that ytterbium trinitrate is very toxic to Hyalella azteca in soft water (7d-LC50 = 0.143 mg/L based on measured concentration). This further supports the decision to apply the worst-case conclusion. The Klimisch 2 data on Danio rerio (see IUCLID section 6.1.1) confirms the toxicity of ytterbium to fish, by demonstrating acute adverse effects on survival, hatching and tail morphology in zebrafish embryos. It has to be noticed that the 96h-LC50 of 3.59 to 35.91 mg/L (expressed in ytterbium trinitrate) is higher than the other LC50 in fish cited above for other rare earth trinitrates. However, another life stage was tested here (i.e. embryo). Considering this life stage could be less sensitive, it was preferred to keep the conclusion very toxic to fish as a matter of safety. Finally, the Klimisch 3 data on Carassius auratus also brings some evidences of the toxicity of ytterbium to enzymatic activities in fish.

 

Toxicity to algae was not considered in this rationale based on the arguments provided in section 6.1.5.

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