Tungsten

Toxicity to microorganisms

Link to relevant study record(s)

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:

2008-09-18 to: 2009-03-13

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well documented, scientifically sound study that was conducted in accordance to GLP and OECD Guideline 209 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 lower transformation/dissolution results for tungsten metal (the target substance) than sodium tungstate (the source substance), the resulting toxicity potential would also be expected to be lower, so read-across is appropriate. In addition, read-across is justified because the classification and labelling is the less severe for the target substance and the PBT/vPvB profile is the same. Finally, the dose descriptor for the target substance is expected to be sufficiently higher than the source chemical, and read-across to the source chemical is adequately protective. For more details refer to the attached description of the read across approach on Annex 3 in the CSR.

Justification for type of information:

1. HYPOTHESIS FOR THE CATEGORY 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: Sodium Tungstate
Target: Tungsten metal
3. CATEGORY APPROACH JUSTIFICATION: See Annex 3 in CSR
4. DATA MATRIX: See Annex 3 in CSR

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

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:

- Concentrations: A stock solution of the test substance was prepared in reagent water at a concentration of 2.00 mg total product/mL. Stock solution volumes of 2.5, 8.0, 25, 80, and 250 mL were added to the 10, 32, 100, 320, and 1,000 mg total product/L test flasks, respectively, for the range finding test. Since there was no appreciable inhibition (eg >50%) up to a nominal of 1,000 mg/L, no further testing was required.

- A stock solution of the reference substance was prepared in reagent water at a concentration of 0.500 mg/mL and was used to add reference substance to the appropriate flasks. Stock solution volumes of 3.2, 10, and 32 mL were added to the 3.2, 10, and 32 mg/L test flasks, respectively.

Vehicle:

no

Details on test solutions:

no data

Test organisms (species):

activated sludge, domestic

Details on inoculum:

-Source of inoculum: Activated sludge, Columbia Wastewater Treatment Plant, Columbia, Missouri
- Preparation of inoculum for exposure: Repeated (11 times) centrifugation of 250 mL aliquots to concentrate the inoculum, followed by 3 rinses in ABC well water, and final suspension in a carboy with stirring and aeration with compressed air. The inoculum was sustained with a synthetic feed solution overnight. Suspended solids concentration was determined in triplicate, and the solution diluted with well water to a final suspended solids concentration between 3.6 and 4.4 g/L.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

30 min

Post exposure observation period:

None

Hardness:

n/a

Test temperature:

19.8-20.2 °C

pH:

8.03- microbial inoculum
8.23-8.35-test flasks, reference, and controls
8.23- abiotic control contact flask (containing no micorbial inoculum)

Dissolved oxygen:

Tested parameter- see Results

Salinity:

n/a

Nominal and measured concentrations:

Nominal concentrations:
Test substance- 0 (control), 10, 32, 100, 320, and 1000 mg test substance/L
Reference substance- 3.2, 10 and 32 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): closed
- Material, size, headspace, fill volume: Glass 1 L, 200 mL inoculum added to flask for 30 min exposure, 500 mL final volume
- Aeration: 500-1000 mL/min
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2 control, 1 abiotic control, 3 concentrations (1 each) reference substance

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: ABC Labs well water

OTHER TEST CONDITIONS
- Adjustment of pH: None
- Light intensity: Ambient

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Oxygen consumption mg/L/hr, one reading per concentration.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2

Reference substance (positive control):

yes

Remarks:

3,5 Dichlorophenol

Duration:

30 min

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

Test Substance:
The test substance showed 12.4, 31.1, 11.3, 14.8, and 17.9% inhibition at concentrations of 10, 32, 100, 320, and 1,000 mg/L, respectively. Thus, the estimated 30-minute-EC50 value for sodium tungstate was estimated to be >1,000 mg (total product)/L and no further testing was required.

Controls:
- Respiration rates for the control flasks were 81.0 and 71.7 mg O2L-1hr-1 during the 30-minute exposure. These respiration rates were within 15% of each other. The respiration rate of the abiotic control was 0.0 mg O2L-1hr-1, indicating that rate of oxygen uptake by sodium tungstate dihydrate was effectively 0% of the mean respiration rate of the controls, 76.4 mg O2L-1hr-1.

Results with reference substance (positive control):

- Results with reference substance valid? Yes. The 30 minute EC50 based on respiration rate for 3,5 dichlorophenol was 14.4 mg/L.
- Relevant effect levels: The percent inhibitions for the three reference toxicant substance flasks were 22.6, 34.3, and 83.8% at 3,5 dichlorophenol nominal concentrations of 3.2, 10, and 32 mg/L, respectively
- Other: 30 min EC50 was 14.4 mg/L- well within the 5-30 mg/L acceptance range required by the method.

Reported statistics and error estimates:

no data

- The ASR system provided the oxygen consumption/depletion curve as a plot of the dissolved oxygen concentration (mg O2/L) versus time (seconds). The analyst selected the appropriate start and end times between which the oxygen depletion curve was linear, and the ASR system automatically calculated the oxygen consumption rate (respiration rate) and expressed these rates as mg O2L-1hr-1.

Conclusions:

The 30 minute EC50 value for sodium tungstate dihydrate to activated sludge is > 1000 mg/ L.

Executive summary:

No microorganisms toxicity data of sufficient quality are available for tungsten metal (target substance). However, microorganisms toxicity data are available for sodium tungstate (source substance), which are used for read-across. Due to lower water solubility and lower toxicity for the target substance compared to the source substance, the resulting read-across from the source substance to the target substance is appropriate as a conservative estimate of potential toxicity for this endpoint. In addition, read-across is appropriate because the PBT/vPvB profile is the same, and the dose descriptors are, or are expected to be, higher for the source substance. For more details, refer to the read-across category approach in the Category section of this IUCLID submission or Annex 3 in the CSR.

Description of key information

A 30-min. EC50 of >1000 mg sodium tungstate/L (586 mg tungsten/L) was found in a OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test) using domestic activated sludge.

Key value for chemical safety assessment

EC50 for microorganisms:

586 mg/L

Additional information

Due to lower transformation/dissolution results for tungsten metal (the target substance) than sodium tungstate (the source substance), the resulting toxicity potential would also be expected to be lower, so read-across is appropriate. In addition, read-across is justified because the classification and labelling is the less severe for the target substance and the PBT/vPvB profile is the same. Finally, the dose descriptor for the target substance is expected to be sufficiently higher than the source chemical, and read-across to the source chemical is adequately protective. For more details, refer to the read-across category approach in the Category section or Annex 3 in the CSR.