Digadolinium trioxide

Endpoint summary

Description of key information

Gadolinium oxide is an inorganic poorly water soluble solid compound which may give rise to very small dissolved gadolinium concentrations in water. Any dissolved gadolinium will be subject to speciation, and because of the complexation behaviour of gadolinium with environmentally relevant ligands such as phosphates, carbonates, etc. under environmentally relevant conditions, and the consequent precipitation of its complexes formed with these ligands, only very small concentrations of dissolved gadolinium can be expected to occur in the aquatic environment.

The behaviour of gadolinium oxide and its capacity to elicit hazardous effects in the environment are assessed following an elemental approach, i.e. with the focus on (dissolved) gadolinium. It is clear that in this respect, hydrolysis resulting in abiotic degradation is not a relevant parameter for this compound. Similarly, biodegradation is not considered relevant for inorganic compounds such as gadolinium oxide.

Although only limited concentrations of dissolved gadolinium are to be expected as a result of potential emissions of gadolinium oxide to the aquatic environment, the gadolinium in solution may adsorb to particulate matter in the relevant environmental compartments or may be taken up by or adsorbed to living organisms. Therefore, the endpoints bioaccumulation and adsorption have been assessed in this dossier.

For aquatic bioaccumulation, a bibliographical review based on ca. 60 publications (1964-2016), containing information on the accumulation of lanthanides (including gadolinium), yttrium and/or zirconium in aquatic organisms, was written to cover this endpoint. Based on the pool of evidence discussed in this review, the overall conclusion was drawn that lanthanides such as gadolinium are unlikely to biomagnify in predatory organisms or humans exposed via the environment.

For adsorption, based on all available information, a log Kp of 5.78 L/kg was obtained for suspended matter-water and a log Kp of 5.15 L/kg was obtained for sediment-water. No sufficiently reliable data have been identified to allow setting a key log Kp value for soil-water. Nevertheless, the overall conclusion is that gadolinium strongly adsorbs to particulate matter. As a result, partitioning to sediment may be expected over time upon release to the aquatic environment.

Gadolinium oxide has no significant vapour pressure and therefore emissions to air could only occur as particulate matter. In such case, gadolinium oxide would end up in the terrestrial and/or aquatic environment through dry or wet deposition.