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Read-across approach

In the assessment of the environmental fate and behaviour of vanadium dioxide, a read-across approach is followed based on all information available for inorganic V compounds. This grouping of vanadium compounds for estimating their properties is based on the assumption that properties are likely to be similar or follow a similar pattern as a result of the presence of the common vanadium ion. After emission of metal compounds to the environment, it is indeed the potentially bioavailable metal ion that is liberated (in greater or lesser amounts) upon contact with water that is the moiety of toxicological concern.

This assumption can be considered valid when

  • differences in solubility among V compounds do not affect the results for behaviour (adsorption, bioaccumulation etc.), and
  • there are no important differences in speciation of vanadium in the environment after emissions of the various V compounds.

The reliable data selected for the environmental fate and behaviour of vanadium are all based on either monitoring data of prevailing elemental vanadium concentrations in water, soil, sediment, suspended matter and organisms or on experimental results with soluble pentavalent (V2O5, NaVO3, NH4VO3 and Na3VO4) or tetravalent (VOSO4 and VOCl2) vanadium substances. Although vanadium dioxide itself is poorly soluble (see IUCLID section 4.8 or chapter 1.3 of the CSR), the liberated vanadium ion will follow the same fate and behaviour in the environment as observed for soluble vanadium substances.

Vanadium can exist in a multitude of different oxidation states from -2 to +5. However, being a first-row transition element, vanadium has the tendency to exist in high oxidation states (+3, +4 and +5), and vanadium ions will form oxy complexes in aqueous solutions (Cotton and Wilkinson, 1988; Crans et al., 1998). The aqueous chemistry of the metal is complex and involves a wide range of oxygenated species for which stabilities depend mainly on the acidity and oxygen level of receiving waters. Under conditions commonly found in oxic fresh waters (i.e., pH between 5 and 9; redox potential [Eh] between 0.5 and 1 V), the pentavalent forms will be the dominant species in solution (Brookins, 1988; Crans et al., 1998; Takeno, 2005). Tetravalent vanadium also may exist under some specific conditions (e.g. pH< 5). It is therefore assumed that upon dissolution of vanadium substances, the environmental conditions control the (redox) speciation of vanadium in water, soil and sediment, regardless of the V compound added.

This is confirmed by redox speciation analysis of dissolved vanadium during transformation/dissolution tests for vanadium metal and 5 vanadium compounds with different oxygenation states (VOSO4, NaVO3, V2O5, V2O3 and FeV) according to OECD guidance document 29 (2009). The tests were conducted at a loading of 1 mg/L over 28 days in standard OECD test media at pH 6 and pH 8 under a set of standard laboratory conditions representative of those in standard OECD aquatic ecotoxicity tests. The redox speciation of dissolved vanadium was measured by separating V(IV) and V(V) species by HPLC and analysis via ICP- MS. Regardless of the original redox state of V in the substance, dissolved V is at both pH 6 and 8 dominantly present as pentavalent V (75-97% of all V), with some traces of V(IV) (Table 1). Recovery of total dissolved V by the measured V(V) and V(IV) was on average 96% and did not differ significantly among the substances tested.

Table 1. Redox speciation of dissolved vanadium after dissolution of various V substances in standard artificial water.

 Substance  Original redox state     After 24 h     After 7 days     After 28 days
     V (IV)  V (V)  V (IV)  V (V)  V (IV)  V (V)
 pH 6              
 NaVO3  V 39*  319 31*  269   <18** 260 
 V2O5  V  76 380  67  329  61  313 
 VOSO4  IV  28* 269  27*  195  <18**  185 
 V2O3  III  5* 79  87  3*  100 
 V  0  <2.1** 16  2*  29  3*  39 
 FeV  0  <2.1** <2.1**  <2.1**  18  28  85 
 pH 8              
 NaVO3  V  37* 336  33*  248  <18**  240 
 V2O5 V 53* 442  33*  368  20*  327 
 VOSO4  IV  <18** 280  69  206  20*  214 
 V2O3  III  4* 65  4*  76  4*  97 
 V  0  <2.1** 22  <2.1**  20  6*  31 
 FeV  0  <2.1** 11  19  78  32  235 

*: extrapolated value below level of quantification (66 µg V/L for NaVO3, V2O5 and VOSO4, 6.6 µg V/L for V2O3, V and FeV); **: below level of detection (18 µg V/L for NaVO3, V2O5 and VOSO4, 2.1 µg V/L for V2O3, V and FeV).

Based on this information, it was concluded that the conditions stated above are met. Therefore, all data based on monitoring data or on soluble V substances (i.e. maximal bioavailability) are used in a read-across approach and results for environmental fate and behaviour are all expressed based on elemental vanadium concentrations.

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