Tungsten dioxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

2008-10-06 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 211 with no deviation to the protocol. The reliability of this study for the substance tested is 1, but in application of read-across to a different substance ECHA’s guidance specifies that the score can be a maximum of 2. On the basis of transformation/dissolution results for tungsten dioxide (the target substance) similar as or lower than sodium tungstate (the source substance), the resulting toxicity potential is also expected to be similar or lower, so read-across is appropriate. Therefore, the dose descriptors are expected to be sufficiently similar or more conservative 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:

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 Dioxide
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 211 (Daphnia magna Reproduction 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:

yes

Details on sampling:

- Concentrations: Control and each treatment level, from freshly prepared solution and on day 0, 9, 14 and 18; and from composites of aged solution on day 2, 11, 16, and 21
- Sampling method: 0.05 mL aliquot of each sample was taken, diluted if necessary with 2 % HNO3, capped and shaken to mix.
- Sample storage conditions before analysis: Room temperature

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: 0.2002 g sodium tungstate dihydrate was dissolved in 2 L aged-blended freshwater. Test concentrations were diluted from this solution.
- Controls: Aged-blended freshwater only
- Evidence of undissolved material: None

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water flea
- Source: In-house daphnid culture
- Age of parental stock: < 24 hours old
- Feeding during test
- Food type: Nanochloropis micro algae and/or the algal species Pseudokirchneriella subcapitata, supplemented by an artificial diet that was prepared according to ABC standard operating procedure.
- Amount: 0.58 mL of 3.0E+07 cells/L, and 0.02 mL of 5 mg/mL artificial diet
- Frequency: At least once a day

ACCLIMATION
- Acclimation period: None, because culturing conditions are the same as test conditions.
- Health during acclimation: No adult mortality observed in the 48 prior to test initiation

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES:
- Individual adults were isolated in a container with fresh food suspention.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Post exposure observation period:

None

Hardness:

130-160 mg/L CaCO3

Test temperature:

19.2-19.9 °C

pH:

8.1-8.5

Dissolved oxygen:

7.2-8.6 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal: 0 (control), 6.5, 13, 25, 50, and 100 mg/L
Time-weighted mean: < MQL, (control), 5.71, 11.5, 21.2, 44.2, and 85.1 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type: Closed
- Material, size, headspace, fill volume: 150 mL glass jars with plastic lids, 80 mL of control and treatment solutions. The test chambers were covered with plastic lids. The test chambers were maintained at 20 ± 1 °C in a temperature-controlled water bath.
- Aeration: None
- Renewal rate of test solution (frequency): Every 2-3 days
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: ABC well water mixed with well water demineralized by reverse osmosis, then aged in a tank containing aquaticorganisms. Water was then passed through a sediment filter, a UV sterilizer, and aerated prior to use.
- Metals: B (0.415 mg/L), Ca (83.1 mg/L), Mg (33.1 mg/L), K (7.93 mg/L), Na (32.2 mg/L); all others below DL.
- Pesticides: Below DL
- Alkalinity: 144-170 mg/L CaCO3
- Conductivity: 340-410 µS/cm
- Culture medium different from test medium: No
- Intervals of water quality measurement: Daily

OTHER TEST CONDITIONS
- Adjustment of pH: No
- Photoperiod: 16 hr light, 8 hr dark, with 30 min simulated dawn and dusk periods
- Light intensity: 443 lux as measured on day 0 with a LI COR Model LI 189 light meter equipped with a photometric sensor.

EFFECT PARAMETERS MEASURED: Mortality, daily

VEHICLE CONTROL PERFORMED: no

RANGE-FINDING STUDY
- Range-finding study was not performed because previous data indicated low toxicity to aquatic organisms.

Reference substance (positive control):

no

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

44.2 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

reproduction

Remarks:

Live young per surviving adult

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

44.2 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

growth

Remarks:

mean length per surviving adult

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

>= 85.1 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

78.7 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

reproduction

Remarks:

Live young per surviving adult

Remarks on result:

other: 95 % CL= 74.5 to 83.0 mg/L

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

> 85.1 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

85.1 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

growth

Remarks:

mean length per surviving adult

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

85.1 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

reproduction

Remarks:

Live young per surviving adult

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

> 85.1 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Remarks:

mean calculated sodium tungstate concentrations

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

immobilisation

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

92.1 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks:

Live young per surviving adult

Remarks on result:

other: 95 % CL = 86.8-97.4 mg/L

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

50 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks:

Live young per surviving adult

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks:

Live young per surviving adult

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth

Remarks:

Mean length per surviving adult

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

50 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth

Remarks:

Mean length per surviving adult

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth

Remarks:

Mean length per surviving adult

Details on results:

Biological Results:
- Mortality of parent animals: 10, 10, 0, 0, 0, and 20 % in the control, 6.5, 13, 25, 50, and 100 mg/L treatments, respectively.
- Mean no. of offspring produced per female: 98, 115, 107, 109, 93, and 40 in the control, 6.5, 13, 25, 50, and 100 mg/L treatments, respectively.
- Mean lengths of daphnids: 4,2, 4.3, 4.3, 4.3, 4.2, and 3.7 mm in the control, 6.5, 13, 25, 50, and 100 mg/L treatments, respectively
- The mortality of the parent animal in the control did not exceed 20 % at the end of the test.  The mean number of live young produced per parent animal surviving at the end of the test was ≥ 60.  The coefficient of variation of the number of living young produced per surviving parent animal in the control was 28 %.  This study is considered to be acceptable and satisfies the guideline requirement for a reproduction test with Daphnia magna.

Reported statistics and error estimates:

All statistical analyses were performed using SAS software. Inferences of statistical significance were based upon a p = 0.05 unless otherwise noted. The no-observed-effect concentration (NOEC) and lowest-observed-effect concentration (LOEC) for mortality/immobility were determined by a one-tailed Dunnett’s test and Fisher’s exact test with the alternative hypothesis being that the mean of the test parameter is lower than the control mean. A Hochberg adjustment was used to control the experiment-wise error rate for Fisher's exact test at the same level (p = 0.05). Reproduction and length data were analyzed with one-way analysis of variance (ANOVA) and a one-tailed Dunnett’s test with the alternate hypothesis being that the mean of the test parameter is lower than the control mean. Prior to the Dunnett’s test, a Shapiro Wilk’s test and a Levene’s test were conducted to test for normality and homogeneity of variance, respectively, over treatments at each time point. The results from the Shapiro-Wilk’s and Levene’s tests indicated that the assumptions of normality and homogeneity of variance were not met for the survival, reproduction, and length data. Therefore, these parameters were analyzed with a non-parametric ANOVA and Dunnett’s test on the ranks of the values. Estimates of the EC50 values and their 95 % confidence limits for reproduction and length were calculated by a four-parameter logistic (sigmoid-shaped) model with two parameters fixed (100 and 0 % inhibition) that were fitted to the data with percent inhibition as the dependent variable and log concentration as the independent variable.

Reported statistics and error estimates (continued):

Estimates of the EC50 concentration values and their 95 % confidence limits for immobilisation were calculated using the probit method and trimmed Spearman-Karber method. When the p value for goodness of fit was > 0.05 and there was no other evidence of questionable convergence, the probit method was selected for reporting.  When this criterion was not met, the trimmed Spearman-Karber method was selected for reporting.

Conclusions:

The 21 day EC50 for survival of D. magna exposed to sodium tungstate dihydrate (reported as time-weighted mean calculated concentrations) was >85.1 mg/L, with an NOEC of >= 85.1 mg/L, and an LOEC of >85.1 mg/L. The 21 day EC50 based on number of young per surviving adult was 78.7 mg/L (95% CL 74.5-83.0 mg/L) , with an NOEC of 44.2 mg/L, and an LOEC of mg/L. The 21 day EC50 based on the mean length per surviving adult was >100 mg/L, with an NOEC of 50 mg/L, and an LOEC of 100 mg/L.

Executive summary:

No long-term toxicity to aquatc invertebrates of sufficient quality are available for tungsten dioxide (target substance). However, long-term toxicity to aquatic invertebrates data are available for sodium tungstate (source substance), which will be 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 classification and labelling is more protective 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 Annex 3 in the CSR.

Description of key information

Tungsten dioxide was not tested for chronic toxicity to invertebrates and read-across to sodium tungstate dihydrate was used for this endpoint. In a reproduction test using Daphnia magna and testing sodium tungstate dihydrate, the 21-day NOEC for reproduction and growth was found to be 44.2 mg/L sodium tungstate dihydrate/L or approximately 25.9 mg W/L). Read-across to sodium tungstate is appropriate as sodium tungstate is of higher solubility under simulated environmental conditions and has the same classification and PBT profile as tungsten dioxide.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

25.9 mg/L

Additional information

Due to similar or lower transformation/dissolution results for tungsten dioxide (the target substance) than sodium tungstate dihydrate (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 description of the read-across category approach.