Zirconium oxide, erbium and yttrium doped

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
The structurally similar read across substance, erbium gadolinium yttrium zirconium oxide is practically insoluble in water. The substance is considered to be a suitable substitute for the registered substance since the only difference between the substance being registered and the read-across substance is that the substance to be registered is missing the gadolinium oxide content (about 1.4 %). The absence of this compound at such a low % is considered highly unlikely to affect its properties.
The water solubility of the read-across substance was determined according to the column elution method. During the study, zirconium was measured because it is the dominant element in the material. Of the other elements, only erbium was measured, because based on comparison of the relative presence of erbium, gadolinium and yttrium in the material, as well as comparison of the water solubility of their oxide forms, erbium was concluded to be the element that would likely be released the most (if any) from the substance when added to water. However, both zirconium and erbium concentrations were below the LOQ (< 0.001 mg/L) in all samples analysed. Therefore the substance can be considered as insoluble in water. Although insoluble, due to their extremely high affinity for phosphate, zirconium, yttrium and lanthanides from poorly soluble compounds (such as their respective oxides) have been observed to affect the dissolved phosphate concentration in algal test media to an extent that algae may suffer from phosphate deprivation, resulting in significant growth inhibition. The observed effects however did not suggest classification of the (insoluble and poorly soluble) zirconium, yttrium and lanthanide compounds tested so far. Further, no tests have been identified yet demonstrating that zirconium, yttrium or lanthanides have a direct toxic effect on algae or other aquatic plants. The phosphate depletion in the test media is a technical issue that - at this point in time - cannot be solved, since it would require the identification of a phosphate complexing agent with higher affinity for phosphate than zirconium, yttrium and lanthanides while not resulting in precipitation of the formed complex from the test medium. Such a complexing agent has not been identified yet. Therefore, and because it is highly unlikely that a phosphate deprivation effect would occur at an environmentally relevant scale (e.g. ecosystem level) due to a hypothetical release of (insoluble or poorly soluble) zirconium, yttrium or lanthanide compounds to the environment, further algal growth inhibition tests with the registered substance, are not expected to provide further insights and are therefore not considered necessary.

Description of key information

In accordance with Column 2 of REACH Annex VII, information requirement section 9.1.2, this study does not need to be conducted since the substance is highly insoluble in water and therefore aquatic toxicity is unlikely to occur.

Additional information

The structurally similar read across substance, erbium gadolinium yttrium zirconium oxide is practically insoluble in water. The substance is considered to be a suitable substitute for the registered substance since the only difference between the substance being registered and the read-across substance is that the substance to be registered is missing the gadolinium oxide content (about 1.4 %). The absence of this compound at such a low % is considered highly unlikely to affect its properties.

The water solubility of the read-across substance was determined according to the column elution method. During the study, zirconium was measured because it is the dominant element in the material. Of the other elements, only erbium was measured, because based on comparison of the relative presence of erbium, gadolinium and yttrium in the material, as well as comparison of the water solubility of their oxide forms, erbium was concluded to be the element that would likely be released the most (if any) from the substance when added to water. However, both zirconium and erbium concentrations were below the LOQ (< 0.001 mg/L) in all samples analysed. Therefore the substance can be considered as insoluble in water. Although insoluble, due to their extremely high affinity for phosphate, zirconium, yttrium and lanthanides from poorly soluble compounds (such as their respective oxides) have been observed to affect the dissolved phosphate concentration in algal test media to an extent that algae may suffer from phosphate deprivation, resulting in significant growth inhibition. The observed effects however did not suggest classification of the (insoluble and poorly soluble) zirconium, yttrium and lanthanide compounds tested so far. Further, no tests have been identified yet demonstrating that zirconium, yttrium or lanthanides have a direct toxic effect on algae or other aquatic plants. The phosphate depletion in the test media is a technical issue that - at this point in time - cannot be solved, since it would require the identification of a phosphate complexing agent with higher affinity for phosphate than zirconium, yttrium and lanthanides while not resulting in precipitation of the formed complex from the test medium. Such a complexing agent has not been identified yet. Therefore, and because it is highly unlikely that a phosphate deprivation effect would occur at an environmentally relevant scale (e.g. ecosystem level) due to a hypothetical release of (insoluble or poorly soluble) zirconium, yttrium or lanthanide compounds to the environment, further algal growth inhibition tests with the registered substance, are not expected to provide further insights and are therefore not considered necessary.