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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
2002-07-01 to: 2002-07-12
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Well documented, scientifically sound study conducted in accordance to GLP and Commission Directive 88/302/EEC with no deviation to the protocol. The reliability of this study for the substance tested is a K1, but in application of read-across to a different substance ECHA’s guidance specifies that the score can be a maximum of K2. Due to similar or lower transformation/dissolution results for tungsten dioxide (the target substance) than tungsten trioxide (the source substance), the resulting toxicity potential would also be expected to be similar or lower, so read-across is appropriate. Therefore, the dose descriptors are expected to be sufficiently similar or higher for the target substance, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read-across approach.
Justification for type of information:
REPORTING FORMAT FOR THE CATEGORY APPROACH
1. HYPOTHESIS FOR THE ANALOGUE APPROACH: The hypothesis is that properties are likely to be similar or follow a similar pattern because of the presence of a common metal ion, in this case tungstate.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES):
Source: Tungsten Trioxide
Target: Tungsten Dioxide
3. CATEGORY APPROACH JUSTIFICATION: See Annex 1 in CSR
4. DATA MATRIX: See Annex 1 in CSR
Reason / purpose:
read-across: supporting information
Qualifier:
according to
Guideline:
other: Commission Directive 88/302/EEC
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
no data
Analytical monitoring:
no
Details on sampling:
no data
Vehicle:
no
Details on test solutions:
The test substance was added to about 130 mL of deionized water and stirred overnight before testing (equilibration phase)
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
no data
Test type:
not specified
Water media type:
not specified
Limit test:
no
Total exposure duration:
3 h
Remarks on exposure duration:
permanent aeration
Post exposure observation period:
no data
Hardness:
no data
Test temperature:
20+2 degree C
pH:
pH of the suspension before application : 6.1
pH of the various test substance concentratoins: 7.2 - 7.4
Dissolved oxygen:
no data
Salinity:
N/A
Nominal and measured concentrations:
Nominal test concentrations (mg/L): 1000, 1800, 3200, 5600, 10000
Details on test conditions:
TEST SYSTEM
- Test vessel: aeration tank of waste water treatment plant treating predominately domestic sewage (Wupper area water authority)
- Test concentration of the activated sludge : 480 mg/L suspended solids
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol (purity of 97%)
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:
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, 10000 of mg/L. The total exposure duration was 3h. 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.
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:

No toxicity to microorganisms data of sufficient quality are available for tungsten dioxide (target substance). However, toxicity to microorganisms data are available for tungsten trioxide (source substance), which will be used for reading across. Due to similar water solubility and toxicity for the target substance compared to the source substance, the resulting read across from the source substance to the target substance is appropriate. In addition, read across is appropriate because the classification and labelling is similar for the source substance than the target substance, the PBT/vPvB profile is the same, and the dose descriptors are, or are expected to be, lower for the source substance. For more details, refer to the read-across category approach included in the Category section of this IUCLID submission and/or as an Annex in the CSR.

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. 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.

Key value for chemical safety assessment

EC50 for microorganisms:
7 900 mg/L
EC10 or NOEC for microorganisms:
7 900 mg/L

Additional information

Due to similar or lower transformation/dissolution results for tungsten dioxide (the target substance) than tungsten trioxide (the source substance), the resulting toxicity potential would also be expected to be similar or lower, so read-across is appropriate. Therefore, the dose descriptors are expected to be sufficiently similar or higher for the target substance, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read-across approach.

The respiration rate of an activated sludge was measured in accordance to GLP and Commission Directive 88/302/EEC after a contact time of 3 hours. The respiration rate of the same activated sludge in the presence of various concentrations of the test substance under otherwise identical conditions was also measured. The inhibitory effect of the test substance at a particular concentration was expressed as a percentage of the mean respiration rates of two controls. An EC50 value was calculated from determinations at different concentrations.

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.