Tungsten dioxide

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Type of information:

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

Adequacy of study:

key study

Study period:

2008-12-30 to 2009-07-23

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 222. A deviation in the protocol included the prepared diet was provided first to the test organisms on the day of test initiation and not one day later as specified by the protocol. There was no effect on the integrity of the study. 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 sodium tungstate (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:

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 222 (Earthworm Reproduction Test (Eisenia fetida/Eisenia andrei))

Deviations:

yes

Remarks:

the prepared diet was provided first to the test organisms on the day of test initiation and not one day later as specified by the protocol but this did not affect the integrity of the study.

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:

no data

Vehicle:

no

Details on preparation and application of test substrate:

A 2.69 mg/mL primary standard was prepared on March 4, 2009, by transferring 5.3755 g of sodium tungstate (5.73 g corrected for purity) to a 2-L volumetric flask and bringing the flask to volume with deionized water. The 2.69 mg/mL primary standard was serially diluted with 2,000 mL volumes of deionized water to prepare working standards at concentrations of 0.169, 0.338, 0.675, and 1.35 mg/mL. A 931 mL aliquot of each working standard solution and the primary standard were added to 2,533.8 grams of air dry soil (equivalent to 2.5 kg of oven dry soil). The soil from the control and each treatment batch was mixed for approximately two to three minutes in a Hamilton Beach commercial mixer. This produced dosed soils with nominal concentrations of 0 (control), 62.9, 126, 251, 503, and 1,000 mg sodium tungstate/kg dry soil and a hydration level of approximately 60% of the soil water holding capacity (i.e., 38.6% moisture). Approximately 831 g of hydrated soil (approximately 600 g dry weight equivalent) was added to each replicate test vessel.

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Details on test organisms:

TEST ORGANISM
- Common name: Earthworms (clitellate adults)
- Source: Vicker’s Farms, Orlando, Florida
- Age at test initiation (mean and range, SD): The adult animals selected for acclimation and testing were approximately 3 months of age with a developed clitellum.
- Weight at test initiation (mean and range, SD): 337 to 595 mg wet weight; initial mean weight of the treatment worms used in this exposure ranged from 411 to 450 mg/worm, based upon the replicate weights of ten worms.
- Weight of control worms at test initiation (mean and range, SD): initial mean weight of the control earthworms used for the definitive exposure was 462 mg/worm based upon the mean of the replicate weights of ten worms in each control replicate.
- The worms were maintained in commercial worm bedding prior to testing.
- An invertebrate diet similar to the diet utilized in the test was provided during the culture period.

ACCLIMATION
- Acclimation period: The adult animals selected for acclimation and testing were approximately 3 months of age with a developed clitellum. Four days prior to test initiation, adult earthworms were removed from the culture bedding and placed in artificial soil to acclimate the worms to the test conditions.
- Acclimation conditions (same as test or not): Same as test
- Health during acclimation (any mortality observed): No mortality observed

Study type:

extended laboratory study

Substrate type:

artificial soil

Limit test:

no

Total exposure duration:

56 d

Post exposure observation period:

no data

Test temperature:

19 to 21 ⁰C

pH:

Soil pH (day 0): 6.09 to 6.45
Soil pH (day 56): 5.59 to 5.73

Moisture:

Soil Moisture (day 0): 37.04 to 38.92%
Soil Moisture (day 56): 44.60 to 48.22%
Soil Moisture at 60% WHC: 38.6%

Details on test conditions:

TEST SYSTEM
- Test container (material, size): The test chambers were glass containers that have an approximate volume of 1.8 L.
- Amount of soil or substrate: A total of 500 or 600 g (dry weight) of prepared soil was added to each test chamber.
- No. of organisms per container (treatment): 10; Each replicate test chamber contained ten worms for a total of 40 worms per test substance treatment.
- No. of replicates per treatment group: four
- No. of replicates per control: Eight replicate test chambers were prepared for the control treatment; Each replicate test chamber contained ten worms for a total of 80 control worms.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Composition (if artificial substrate): The artificial soil used for both definitive exposures was prepared to approximate a sandy loam soil by mixing the following ratio of constituents: 70% silica sand, 20% kaolin clay, and 10% sphagnum peat based on dry weight equivalents. Calcium carbonate, CaCO3, was added to the soil to adjust the pH to fall within the 6.5 ± 0.5 range specified by the protocol. The peat moss was sieved to a finely ground consistency and did not contain any visible plant remains.
- Organic carbon (%): low total content
- Maximum water holding capacity (in % dry weigth): The water holding capacity (WHC) was determined to be 64.4 mL per 100 grams dry soil for the soil used in the definitive exposure.
- Storage (condition, duration): After preparation, the soil was stored at room temperature.

OTHER TEST CONDITIONS
- Photoperiod: 16-hr light to 8-hr dark
- Light intensity: 560.8 to 708.1 lux

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: A 28-day range-finding test was conducted using nominal concentrations of 0 (control), 1.0, 10, 100, and 1,000 mg/kg dry soil. Two replicates were used for the control and test substance treatments with 10 worms added per replicate.
- Results used to determine the conditions for the definitive study: After 28 days there was no mortality or sublethal effects observed in the control or test substance treatments. At the termination of the range-finding test there was an average of 34, 33, 31, 30, and 28 cocoons per replicate for the control, 1.0, 10, 100, and 1,000 mg/kg dry soil treatments, respectively. Based on these results, a definitive test was performed at target nominal
concentrations of 0 (control), 62.5, 125, 250, 500, and 1,000 mg/kg dry soil.

Nominal and measured concentrations:

Calculated Nominal Soil Concentrations: 0 (Control), 62.9, 126, 251, 503, and 1,000 mg/kg dry soil

Duration:

56 d

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks on result:

other: The highest concentration tested

Duration:

56 d

Dose descriptor:

LOEC

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks on result:

other: The highest concentration tested

Duration:

56 d

Dose descriptor:

EC10

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks on result:

other: The highest concentration tested

Duration:

56 d

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Remarks on result:

other: The highest concentration tested

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: survival

Remarks on result:

other: The highest concentration tested

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: suvival

Remarks on result:

other: The highest concentration tested

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: survival

Remarks on result:

other: The highest concentration tested

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: survival

Remarks on result:

other: The highest concentration tested

Details on results:

- Mortality at end of exposure period: After 28 days of exposure to sodium tungstate, percent mortality of the adult worms was 0% in the control and all treatment.
- Other biological observations: Observations of general health and behavior of the worms were also noted (i.e., normal, lethargic, softness, absence of burrowing, and discoloration). All of the live earthworms were normal in appearance and behavior with the exception of five lethargic worms in the 1,000 mg/Kg dry soil treatment. No abnormal burrowing or avoidance behaviors were recorded during testing.
- The weights of surviving earthworms were measured on a replicate basis. The control worms gained an average of 2.164 g per replicate or 47% in replicate mass during the 28-day exposure . The treatment worms also gained weight during the study. The mean replicate weight gain of the surviving treatment animals ranged from 2.004 to 2.671 grams. The mean percent weight gain for the treatment animals ranged from 47 to 65% in replicate animal mass over the initial 28 days of exposure.
- At test termination, the number of juvenile worms will be determined by rinsing the test soil through a series of sieves (e.g., 710, 500, and 425 um mesh), collecting and enumerating the animals retained within the sieves.
- The average reproduction for the control animals was 547 juveniles per replicate. The percent coefficient of variation (%CV) for the control data was 14%. The average reproduction values were 447, 447, 483, 459, and 518 juveniles for nominal concentrations of 62.9, 126, 251, 503, and 1,000 mg sodium tungstate per kilogram dry soil treatments, respectively. There was no statistically significant reduction (p < 0.05) in the reproductive output of the adult worms exposed to the test substance. The EC10 and EC50 for reproduction was > 1,000 mg sodium tungstate/kg dry soil, the highest concentration tested. The NOEC and LOEC for reproduction was 1,000 and > 1,000 mg sodium tungstate/kg dry soil, respectively.
- The survival of the control adult animals was 100%, which met the acceptability of the test protocol and guidance document. Each control replicate containing 10 adult worms after the first 28 days of exposure produced more than the minimum acceptability criterion of 30 juvenile worms and the %CV value for the control reproduction was less than the maximum acceptability of 30% as specified by the protocol and the test guideline.

Results with reference substance (positive control):

- The analytical reference substance, Tungsten ICP Standard (1,000 ppm W) was received from Ricca Chemical Company on September 11, 2008, and was stored at room temperature. The sample was assigned ABC reference no. PS-22260. A certificate of analysis reported the concentration of solution to be 1,000 ppm W (Appendix A). This material was used to prepare analytical reference standard solutions. All solutions were corrected for the purity of the reference substance.

The reference substance (ie toxic standard) was carbendazim (received from Chem Service (West Chester, Pennsylvania)). The certificate of analysis showed the purity to be 99.4%

Reported statistics and error estimates:

All statistical analyses were performed using SAS software. Inferences of statistical significance were based upon p ≤ 0.05. Since there was no mortality in the control or treatments the noobserved-effect concentration (NOEC) for the survival data was equal to the highest level tested. The reproduction NOEC value was estimated using a one-way analysis of variance (ANOVA) procedure and a one-tailed Dunnett's test. Prior to the Dunnett's test, a Shapiro-Wilk’s and the Levene’s tests were performed to determine data normality and homogeneity of the treatment variances. The reproductive data met the criterion for normality and homogeneity of variance, therefore a parametric analysis was performed on the reproductive data.

The soil moisture and pH were measured in samples collected from the parent control and treatment soils on day 0. At test termination (study day 56), the moisture content and soil pH were determined from samples of test medium collected from a single replicate test chamber (ie replicate A) for all treatment levels. The soil samples were collected prior to the enumeration of the juvenile worms. The pH was measured using a WTW Model pH 330i pH meter. The percent moisture was calculated as the difference between the wet and dry soil samples and presented as percent of the soil dry weight using a Mettler Toledo HR73 Halogen Moisture Analyzer. A continuous temperature record was measured with an electronic data logger in a chamber containing moistened control soil and placed in the water bath. Light intensity was measured at test initiation with a LI-COR Model LI-189 light meter equipped with a photometric sensor.

Validity criteria fulfilled:

yes

Conclusions:

The survival of the control adult animals was 100%, which met the acceptability of the test protocol and guidance document. Each control replicate containing 10 adult worms after the first 28 days of exposure produced more than the minimum acceptability criterion of 30 juvenile worms and the %CV value for the control reproduction was less than the maximum acceptability of 30% as specified by the protocol and the test guideline.

Under the conditions of this study and based upon nominal concentrations, the 56-day reproduction NOEC value was 1,000 mg sodium tungstate/kg dry soil and the estimated EC10 and EC50 value for average reproduction was > 1,000 mg sodium tungstate/kg, the highest concentration tested.

Description of key information

Tungsten dioxide was not tested for toxicity to soil macro-organisms and read-across to sodium tungstate was used for this endpoint. In a 56-day long-term toxicity study, earthworms (Eisenia fetida) were exposed to sodium tungstate at calculated nominal soil concentrations of 0 (Control), 62.9, 126, 251, 503, and 1,000 mg/kg dry soil. The experiment was carried out in accordance with OECD Guideline 222. The 56-day NOEC, based on reproduction, was 1,000 mg/kg dw of soil/substrate. The LOEC, based on reproduction was > 1000 mg/kg dw of soil (626 mg W/kg dry soil). Tungsten dioxide is considered to be non-toxic to earthworms up to the concentration of 1,000 mg/kg dw of soil.

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for soil macroorganisms:

626 mg/kg soil dw

Additional information

Due to similar or lower transformation/dissolution results for tungsten dioxide (the target substance) than sodium tungstate (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.