Ammonium wolframate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.574 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.705 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:

70 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

1 630 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

163 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:

no potential for bioaccumulation

Additional information

All PNECs derived are in concentration of tungsten ion, as toxicity is expected to occur from the metal ion.

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, Annex 10) [see Table 4 in Section 1.3 for results] with toxicity data for the soluble metal substance as described in the CLP technical guidance (section IV. 5 Application of classification criteria to metals and metal compounds) (EU, 2008). The T/D data is 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 ammonium paratungstate was derived at pH 8.5 (24-hour T/D testing) and found to be equal to 67200 μg tungsten/L (67.2 mg tungsten/L)(CANMET-MMSL, 2010). This T/D value was compared to the aquatic toxicity reference value derived as the lowest acute effect level from studies using sodium tungstate. In the context of the classification scheme for metals and metal compounds, the toxicity value of the metal ion (tungsten) is derived from the sodium tungstate toxicity testing of algae (E_rC50). This is the value used for toxicity classifications of all inorganic tungsten substances since the tungsten is readily soluble from sodium tungstate and the toxicity is not affected by the sodium anion. Since the toxicity of tungsten in ammonium paratungstate is potentially affected by the ammonium anion (see section 7.1.2 for more details), it is not appropriate to use the ammonium paratungstate toxicity value to evaluate the tungsten metal ion toxicity. The reference value was thus determined to be 31.0 mg tungsten/L based on the acute acceptable toxicity of sodium tungstate to algae (see section 7.1.2 for more details). Since the dissolution of ammonium paratungstate (67.2 mg tungsten/L) is greater than the reference toxicity value (31.0 mg tungsten/L, based on the E_rC50 from the algal inhibition test with sodium tungstate), the reference toxicity value based on tungsten ion concentration is then corrected for the molecular weight of ammonium paratungstate to determine its classification. This calculation is conducted as follows:

31.0 mg tungsten/L = 0.0310 g W/L

0.0310 g W/L x (1 mol W/183.84 g) x (1 mol APT/12 mol W) x (3132.2 g APT/1 mol APT) = 0.0440 g APT/L

0.0440 g APT/L = 44.0 mg APT/L

This toxicity value is used for classification by comparing to the aquatic toxicity cut-off values for classification. Since 44 mg APT/L is >10 mg/L and ≤100 mg/L, ammonium wolframate classifies as Acute Category 3 for aquatic toxicity according to the CLP. However, since the lowest no effect chronic value 4.80 mg ammonium wolframate/L (3.38 mg tungsten/L, based on the chronic reference value determined for sodium tungstate (E_rC10) and corrected for molecular weight of ammonium paratungstate) is greater than 1 mg/L, ammonium paratungstate 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 (eg 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).