Disodium wolframate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.338 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.31 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.034 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

5.86 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

960 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

96 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

2.17 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

0.011 g/kg food

Assessment factor:

90

Additional information

All PNECs derived are in concentration of tungsten ion, as toxicity is expected to occur from the metal ion. In addition, the concentrations of inorganic ions present in typical ecotoxicity test media are in the mg/L-range, and well below the toxic thresholds of these ions for the test organisms of interest. On the other hand, the toxic threshold concentrations of several metals are in the µg/L-range, which is orders of magnitude lower. Therefore, the added counter-ions (e.g. sodium) dissociating from sodium tungstate, do not contribute significantly to the observed effect of the metal ion (eg. tungstate) on the test organism (for additional information on the counter ion effects refer to Annex 3 -Read-Across-Tungstate Category Approach).

Conclusion on classification

Aquatic toxicity classification of inorganic metals and metal compounds is conducted by comparing transformation/dissolution (T/D) data for the substance, generated using the standard protocol (UN GHS, 2007, Annex 10) [see Table 3 in Section 1.3 for results], with toxicity data for the most soluble metal substance as described in the CLP technical guidance (section IV. 5 Application of classification criteria to metals and metal compounds) (EU, 2008). In the case of sodium tungstate, T/D data for sodium tungstate are compared to the aquatic toxicity reference values of sodium tungstate. The T/D data are ideally tested at the pH at which the highest dissolution is expected, within the range defined by the test protocol (pH 5.5-8.5). Since inorganic tungsten substances have been demonstrated to have a higher T/D rate at pH 8.5 than pH 6, the data used for aquatic toxicity classification of sodium tungstate was derived at pH 8.5 (24-hour T/D testing) and found to be equal to 66900 μg W/L (CANMET-MMSL, 2010). These T/D values were compared to the acute aquatic toxicity reference value (31000 μg W/L, based on the ErC50) derived from sodium tungstate testing of algae, as the most sensitive standard aquatic species for sodium tungstate. Since the dissolution of sodium tungstate (66900 μg W/L) is more than the tungsten ion toxicity value (31000 μg W/L) derived from sodium tungstate testing, the toxicity value of the tungsten ion is then corrected for the molecular weight of sodium tungstate to determine its classification. This calculation is conducted as follows:

 

31000 μg W/L = 0.0310 g W/L

0.031 g W/L x (1 mol W/183.84 g) x (1 mol sodium tungstate/1 mol W) x (293.8 g sodium tungstate/1 mol sodium tungstate) = 0.0495 g sodium tungstate/L

0.0495 g sodium tungstate/L = 49.5 mg sodium tungstate/L

 

This toxicity value is used for classification by comparing to the aquatic toxicity cut-off values for classification. Since the acute value (49.5 mg sodium tungstate/L) is greater than 10 mg/L and less than or equal to100 mg/L, sodium tungstate classifies as Acute Category 3 for aquatic toxicity according to the CLP. However, since the lowest no effect chronic value of 5.76 mg for sodium tungstate/L, based on the ErC10 (3.38 mg tungsten/L) is greater than 1 mg/L, sodium tungstate does not receive an acute or chronic classification.

 

The CLP classification scheme for evaluating aquatic toxicity of metals and metal compounds is the same as that used to classify metals and metal compounds under the Dangerous Substances Directive, with the exception of the name of the classifications (e.g. DSD cites R phrases, CLP uses acute and chronic categories). Although the DSD does not specifically cite the classification scheme for metals and metal compounds, the scheme was outlined in the ECB documents used in the classification of nickel metal (massive and powder). In addition, this classification scheme was used to evaluate aquatic toxicity of nickel metal and some copper compounds (ECB, 2001; ECB, 2005).