Registration Dossier
Registration Dossier
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EC number: 235-013-2 | CAS number: 12055-23-1
Endpoint summary
Administrative data
Description of key information
Additional information
Hafnium dioxide is a stable compound present in the environment, poorly water soluble and quite inert. Hf(OH)22+is the hydrated form of HfO2 and is therefore taken into consideration for behavior of HfO2 in the environment.
Degradation:
Concerning degradation, HfO2 cannot be degraded in a biotic way because it is an inorganic element, and it is not relevant to consider a hydrolysis test because of the very low solubility in water.
Bioaccumulation:
The extremely low water solubility of HfO2 <5 µg/L and its affinity to form complexes with organic matter (Kd values are reported for Hf metal, with a range of 1500 – 8500 L/kg: that show a strong affinity of the metal for particulate matter) make HfO2 very unlikely to be bioavailable to aquatic organisms, fish and then fish-eating predators. No potential for bioaccumulation is then expected.
Adsorption:
In the terrestrial compartment, the availability of metal compounds for uptake by biota can differ from site to site and may change over time due to many processes, including weathering and (de)sorption processes. It should also be noted that Kd are accurate only during an equilibrium state, which is difficult to reach for metals in the environment. As a consequence, part of the metal present in the solid phase may be encapsulated in the mineral fraction and is therefore not available.
The IAEA Technical Reports Series No. 364 (Handbook of Parameter Values for the Prediction of Radionuclide Transfer in Temperate Environments, 1994) publication reported Kd values for Hf within the range of 1500 to 5400 L/kg, with a Kd of 2500 L/kg for all soils in general.
These values and IAEA assessor were considered reliable enough to be used for HfO2, as the common metal form Hf is retrieved in soils.
The typical value kept for assessment: Kd of 2500 L/kg. This coefficient confirmed a high adsorptivity of the substance on particulate matter and low mobility in soils, leading to a poor availability to biota via interstitial water.
Atmospheric behavior:
Volatilization can be ignored for metals compounds, except for mercury compounds and several organometallic compounds.
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