Registration Dossier

Categories

Categories

Category name:
Tungstate Speciation Read Across Category

Justifications and discussions

Category definition:
The read across approach has generally been based on the occurrence of a common metal ion or anion and the use of read-across to fill data gaps
Category order description:
The read across approach is to read from sparingly soluble to the water-soluble category, but not the other way around.
Category rationale:
1. CATEGORY HYPOTHESIS
The main assumption is that it is the metal ion that is responsible for the effects to be assessed. Since the toxicity of metals and their inorganic substances is primarily associated with the release of soluble metal ions, their bioavailability is defined as the extent to which the soluble metal ion is available at the target organ/site.

2. CATEGORY JUSTIFICATION
The basis of this read-across category approach is the relative bioavailability of tungstate at target site(s) that in most cases determines the potential occurrence and the severity of the systemic effects to be assessed for the read-across of tungsten substances. Therefore, tungsten substances of similar release of the tungsten ionic species at the exposure site are expected to result in similar systemic and local toxicity (provided there is not an effect of physical form on the toxicity).
With the help of T/D, bioaccessibility (bioelution), and toxicokinetic studies the read-across category approach was confirmed and justified. Once the tungstate speciation has been established and together with WO42- bioavailability in simulated human fluids a read-across grouping and hierarchy for tungsten-bearing sparingly water-soluble and water-soluble substances was established.

3. APPLICABILITY DOMAIN OF THE CATEGORY
Once the tungstate speciation has been established and based on WO42- bioavailability in simulated human fluids the following read-across grouping and hierarchy for tungsten-bearing sparingly water-soluble and water-soluble substances can be established:
Grouping 1: Tungsten Disulphide, Tungsten Metal, Tungsten Carbide, Reaction Mass of ditungsten carbide and tungsten carbide
Grouping 2: Tungsten Trioxide and its hydrated form Tungstic Acid, and Tungsten Oxide
Grouping 3: Sodium Tungstate, Ammonium Metatungstate and Ammonium Paratungstate
If no relevant REACH endpoint information is available the approach is to read-across within the same bioavailability group, and if there is it no data within the same group, then the read-across should be conducted using data of the next group, but always read-across from sparingly soluble to the water-soluble category, but not the other way around.