Terbium trinitrate

Endpoint summary

Description of key information

Terbium 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. Considering the importance of those parameters in the determination of environmental classification, biotic/abiotic degradation and bioaccumulation were further investigated:

 

Biotic degradation:

According to column 2 of REACH Annex VII, the study does not need to be performed for inorganic substances as terbium trinitrate.

 

Abiotic degradation:

According to REACH Annex XI, testing for a specific endpoint may be omitted if testing does not appear to be scientifically necessary or if it is technically not possible to conduct the study as a consequence of the properties of the substance. Under REACH (ECHA 2016, Chapter R.7B - Endpoint Specific Guidance), the term "hydrolysis" refers to the "decomposition or degradation of a chemical by reaction with water", and this as a function of pH. In the case of inorganic substances, like terbium trinitrate, the assessment of environmental fate is generally based on the elemental concentration, regardless of the element's speciation which depends on the prevailing environmental conditions. In other words, formation of different terbium species may occur in the environment, but discriminating those species will add no value to the environmental fate assessment. The element-based evaluation (pooling all speciation forms together) can be effectively considered as a worst-case assumption. As a result, abiotic processes, like degradation or transformation by reaction with water, are irrelevant for inorganic substances as long as they are assessed on an elemental basis.

 

Bioaccumulation:

A bibliographical review based on ca. 60 publications (1964-2016), containing information on the accumulation of lanthanides (including terbium, the rare earth element under consideration in this registration dossier), yttrium and/or zirconium in aquatic organisms, was written to cover this endpoint. Because of the similarity between findings for the elements under consideration and those for (other) metals, such as the influence of environmental conditions on bioaccumulation, the observation of inverse relationships between bioaccumulation values and concentrations in water, and the evidence for the existence of internal regulatory mechanisms, the bioaccumulation thresholds (e.g. for classification) used for organic substances are considered not applicable, and the evaluation of aquatic bioaccumulation was evaluated through expert judgment. This has led to the following conclusions:

•A considerable decrease of bioaccumulation was observed when ascending the trophic levels, this being obvious when comparing data in fish to those in lower trophic levels.

•Lanthanides, yttrium and zirconium do not biomagnify through the aquatic food web.

Based on this pool of evidence, it was concluded that lanthanides, yttrium and zirconium are unlikely to biomagnify in predatory organisms or humans exposed via the environment.