Hexaammonium 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):

0.31 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.057 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

No ecotoxicological toxicity data of sufficient quality are available for ammonium metatungstate (target substance). However, ecotoxicological data are available for ammonium paratungstate, sodium metatungstate and sodium tungstate (source substances). Due to similar or lower transformation/dissolution results for the target substance than the source substances, the resulting toxicity potential is expected to be similar or lower, so read-across is appropriate. In addition, read-across is justified because the classification and labelling is the same or less severe for the target substance and the PBT/vPvB profile is the same. Finally, the dose descriptors are, or are expected to be, sufficiently similar or higher for the target substance, and read-across to the source chemicals is adequately protective. For more details, refer to the read-across category approach description in the Category section of this IUCLID submission or Annex 3 of the CSR.

It is necessary, however, to note that in addition to dissociated tungstate anion, there will also be dissociated ammonium cations when ammonium metatungstate (AMT) dissociates in solution. The ammonium and the corresponding non-ionised ammonia, which exist in equilibrium in aqueous solutions, are widely known to be toxic to fish and aquatic invertebrates, with the extent of adverse effects and fraction of each form present, dependent upon temperature and pH (non-ionised ammonia being the more toxic form). While the toxicity of the ammonia/ammonium to aquatic species has been documented, effect concentrations (and the corresponding PNECs) for studies presented in the CSR are presented in terms of the soluble tungsten anion for the following reasons. First, ammonium paratungstate (APT) contains 10 moles of ammonium whereas AMT only contains 6 moles of ammonium, and, therefore, any ammonia/ammonium effects are taken into account using APT data. Second, the most sensitive species (P. subcapitata) in the available dataset of read-across substances was tested with both APT (which contains both ammonium and tungstate) and sodium tungstate. The resulting ErC10 for sodium tungstate was approximately 6.3 times more toxic than with APT, demonstrating that ammonia/ammonium is not the primary driver of toxicity. Hence, the toxicity of the tungsten ion, and not that of ammonia, are used in the risk assessment.

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) 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 transformation/dissolution (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 metatungstate was derived at pH 8.5 (24-hour T/D testing) and found to be equal to 67,200 ug W/L (67.2 mg W/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. 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 metatungstate (AMT) is potentially affected by the ammonium cation, it is not appropriate to use the toxicity values of ammonium-containing tungsten compounds to evaluate the tungsten metal ion toxicity. The toxicity of the tungsten metal ion was calculated by multiplying the toxicity value of the tungsten compound by the molar fraction of tungsten in that compound. Using this calculation, the reference concentration was thus determined to be 31.0 mg W/L based on the acute acceptable toxicity of sodium tungstate to green algae (P. subcapitata). Since the anticipated dissolution of AMT (65.5 mg W/L) is greater than the reference toxicity value (31.0 mg W/L), the reference toxicity concentration based on tungsten ion concentration is then corrected for the molecular weight of AMT to determine its classification. This calculation is as follows:

Acute reference concentration correction:

31.0 mg W/L x (1 mmol W/183.84 mg) x (1 mmol AMT/12 mmol W) x (3132.2 mg AMT/1 mmol AMT) = 44.0 mg AMT/L

Chronic reference concentration correction:

3.38 mg W/L x (1 mmol W/183.84 mg) x (1 mmol AMT/12 mmol W) x (3132.2 mg AMT/1 mmol AMT) = 4.80 mg AMT/L

These reference toxicity concentrations are used for classification by comparison to the aquatic toxicity cut-off values for classification. Since the lowest acute toxicity value for sodium tungstate translates to a 96-h ErC50 of 44 mg AMT/L for P. subcapitata, which is >10 mg/L and ≤100 mg/L, this datum meets the first criterion for classification as a Chronic Category 3 aquatic toxicant. However, chronic algal for sodium tungstate, a 96-h ErC10 of 3.38 mg W/L for P. subcapitata, translates to 4.80 mg AMT/L, which does not meet the second criterion for Chronic Category 3 classification: a chronic toxicity NOEC ≤ 1 mg/L. Therefore, AMT does not classify for Chronic Category 3 for aquatic toxicity.

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 (DSD), 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).

References:

CANMET-MMSL.2010. Transformation/Dissolution Studies on tungsten Compounds and Metal. Report No. 09-005(CR). Owner Company: International Tungsten Industry Association. Report Date: June, 2010

 

ECB (European Chemicals Bureau), 2001. ECBI/07/01 Rev. 3, 10 December 2001. SUMMARY RECORD: Commission Working Group on the Classification and Labelling of Dangerous Substances. Meeting on Environmental Effects. ECB - Ispra, 28 February - 2 March 2001.

 

ECB (European Chemicals Bureau), 2005. ECBI/124/04 Rev. 1, 11 July, 2005. Draft Summary Record: Commission Working Group on the Classification and Labelling of Dangerous Substances. Meeting on Environmental Effects of Existing Chemicals, Pesticides & New Chemicals. ECB - Ispra, September 15 - 17, 2004.

 

Official Journal of the European Union (EU), 2008. Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006

 

UN GHS (United Nations Globally Harmonized System of Classification and Labeling of Chemicals), 2007. Annex 10. Guidance on Transformation/Dissolution of Metals and Metal Compounds. http://www.unece.org/trans/danger/publi/ghs/ghs_rev02/02files_e.html