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Tungsten dioxide was not tested for acute and chronic aquatic toxicity and read-across to tungsten trioxide and/or sodium tungstate was used for these endpoints. The speciation work in the T/D studies (see IUCLID section 4.8) supports the read-across approach for tungsten substances and confirms that properties are likely to be similar or follow a similar pattern as a result of the release of a common WO42-ion. As such, the data available on Na2WO4 (or sodium tungstate dihydrate) can be used to estimate the worst-case systemic toxicity and ecotoxicity in order to address data gaps for WO2. These data support read across between WO2 and WO3 as tungsten substance of slightly higher water solubility (→ T/D protocol) being protective for WO2. Read-across from Na2WO4 as highly soluble tungsten substance can be used as an estimate of worst-case toxicity.

 

The short-term toxicity of sodium tungstate to fish and aquatic invertebrates was determined to be LC50 > 181 mg sodium tungstate/L (~106 mg W/L) and EC50 > 163 mg sodium tungstate/L (~ 95.5 mg W/L), respectively.

Algae was more sensitive to sodium tungstate with an ErC50 of 52.9 mg sodium tungstate (33.10 mg tungsten/L), an ErC10 of 6.54 sodium tungstate (3.83 mg tungsten/L) and a NOEC (based on growth rate) of 0.85 sodium tungstate. The ErC10 from this study was considered to be more appropriate and will be carried forward to the classification and risk characterization.

 

In addition to the test regarding acute toxicity to fish and aquatic invertebrates chronic studies have been conducted with sodium tungstate. The NOEC determined in an early-life stage test on zebra fish was found to be greater than or equal to the highest concentration tested (≥ 9.82 mg sodium tungstate/L or approximately 5.74 mg W/L). The 21-day NOEC for reproduction and growth of daphnia magna was found to be 44.2 mg/L sodium tungstate dihydrate/L (or approximately 25.9 mg W/L).

 

Besides, tungsten trioxide was tested for toxicity to microorganisms and read-across to tungsten dioxide was used for this endpoint. Tungsten trioxide showed 3.1% respiration inhibition of activated sludge at the test substance concentration of 10,000 mg/L. The EC50 was determined to be > 10,000 mg/L. Tungsten trioxide showed 3.1 % respiration inhibition of activated sludge at a test substance concentration of 10,000 mg/L (corresponding to 7,900 mg W/L). Therefore, this value being between the NOEC and EC10 is further considered the assessment.

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