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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
This information is used in a read-across approach in the assessment of the target substance.
Reason / purpose for cross-reference:
read-across source
GLP compliance:
yes
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 10 000 mg/L
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
- Tungsten trioxide showed 3.1 % respiration inhibition of activated sludge at a test substance concentration of 10,000 mg/L.
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- Relevant effect levels: EC50 = 6.1 mg/L
Reported statistics and error estimates:
- The EC values were determined by statistical methods (probit analysis)

Test concentration: 1000 mg/L - Inhibition: 0.0 % Test Concentration: 1800 mg/L - Inhibition: 15.4 % Test Concentration: 3200 mg/L - Inhibition: 7.7 % Test Concentration: 5600 mg/L - Inhibition: 7.7 % Test Concentration: 10000 mg/L - Inhibition: 3.1 % Physical-Chemical oxygen consumption was 0 mg/L/h for all test concentrations. The Respiratory rate-physical-chemical oxygen consumption ranged from 22.0 mg/L/h to 27.0 mg/L/h

Conclusions:
Tungsten trioxide showed 3.1 % respiration inhibition of activated sludge at the test substance concentration of 10,000 mg/L. The EC50 > 10,000 mg/L
Executive summary:

The effect of tungsten trioxide on the respiration of activated sludge microorganisms (predominantly domestic sewage) was tested in accordance with OECD Guideline 209 at nominal test concentrations of 1000, 1800, 3200, 5600, and 10000 mg/L. The total exposure duration was 3 h. Tungsten trioxide showed 3.1% respiration inhibition of activated sludge at the test substance concentration of 10,000 mg/L. The EC50 is above 10,000 mg/L.

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Description of key information

Tungsten dioxide was not tested for toxicity to microorganisms and read-across to tungsten trioxide 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 (corresponding to 7,900 mg W/L). The EC50 was determined to be > 10,000 mg/L.

This information is used in a read-across approach in the assessment of the target substance.

For details and justification of read-across please refer to the attached report in section 13 of IUCLID.

Recalculation of this values to the corresponding concentrations of tungsten hexachloride result in a theoretic value of EC50 > 17,000 mg WCl6/L

However, this value considerably exceeds the water solubility of the substance which is in the range of 20 - 46.1 µg/L and 44.8 µg/L after adjustment to pH 7 (Golz, 2017). Therefore, no adverse effects in microorganisms are expected through the amount of soluble tungsten ions released from tungsten hexachloride in water.

Key value for chemical safety assessment

Additional information