Tungsten carbide

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation: terrestrial

Type of information:

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

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Accumulation data in earthworms were obtained after use in a toxicity study conducted according to modified ISO 11268-1 (Effects of Pollutants on Earthworms. 1. Determination of Acute Toxicity Using Artificial Soil Substrate), with sufficient information presented on materials and methods to adequately evaluate bioaccumulation results. Insufficient information was available on the levels of background tungsten, other metals, and environmental contaminants in the soil tested.

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: Tungsten metal
Target: Tungsten carbide
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

Principles of method if other than guideline:

Accumulation data in earthworms were obtained after use in a toxicity study conducted according to modified ISO 11268-1 (Effects of Pollutants on Earthworms. 1. Determination of Acute Toxicity Using Artificial Soil Substrate).

GLP compliance:

not specified

Radiolabelling:

no

Details on sampling:

- Sampling intervals/frequency for test organisms: After the 80 day exposure period, the surviving worms were collected.and placed in jars containing wet filter paper and no soil.
- Sample storage conditions before analysis: worms were placed in jars containing wet filter paper and no soil for 2 days.
- Details on sampling and analysis of test organisms and test media samples (e.g. sample preparation, analytical methods): Worms were frozen in liquid nitrogen, acid digested, and tungsten concentration measured by ICP.

Vehicle:

no

Details on preparation and application of test substrate:

- Method of mixing into soil (if used): mixed manually with tungsten powder
- Controls: Non-treated highway soil

Test organisms (species):

Eisenia fetida

Details on test organisms:

- Common name: Earthworm
- Source: Worm Farm Inc. Monroe Twp, NJ
- Age at test initiation (mean and range, SD): Not specified
- Weight at test initiation (mean and range, SD): Not specified

Total exposure / uptake duration:

80 d

Total depuration duration:

2 d

Test temperature:

Room temperature

pH:

Varied with tungsten concentration, 4.80-7.25.

TOC:

- Organic carbon (%): 2 %

Moisture:

Not specified; DI water added daily.

Details on test conditions:

TEST SYSTEM
- Test container (material, size): glass jar, covered with filter paper
- Amount of soil or substrate: 750 g
- No. of organisms per container (treatment): 10
- No. of replicates per treatment group: 3 or 4
- No. of replicates per control: 3 or 4
- One set of replicates ammended with 10,000 mg/kg CaCO3 in addition to the toxicant to
buffer pH change.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographic location: Highway soil (Exit 40, Hwy 78, The Plainfields, NJ)
- Pesticide use history at the collection site: Not specified
- Sampling depth (cm): 1-5 cm
- Organic carbon (%): 2 %
- Pretreatment of soil: Homogenized, plant roots and large particles removed, sieved through a
1 mm sieve.
- Storage (condition, duration): 4 °C until use- more than 1 year.

Nominal and measured concentrations:

Nominal-Control, 10, 100 and 10,000 mg/kg tungsten.

Key result

Type:

BCF

Value:

>= 0.03 - <= 0.35 dimensionless

Basis:

whole body d.w.

Time of plateau:

14 d

Calculation basis:

steady state

Remarks:

For soil concentrations of 10 and 1000 mg W/Kg soil

Kinetic parameters:

No data

Metabolites:

No data

Details on results:

Test with non-aged soil
- Mortality of test organisms: All worms in the 10 and 100 mg W/kg soil levels survived for 80 days. All worms in the 10,000 mg/kg soil died after 80 days.
- Other biological observations: All worms in all concentrations survived after 80 days in the soils amended with 10,000 mg/kg CaCO3. The pH of the soil decreased over time from its initial value of 5.6 in all soils without a CaCO3 supplement. The largest drop observed for the highest W concentration where a final soil pH of 4.80 was measured. However, for the replicates containing the same W concentration and supplemented with CaCO3, the pH after 80 days was 7.25.
- Mortality and/or behavioural abnormalities of control: all worms in the control group survived.
- Worms took up and accumulated tungsten in their tissue. Dry weight tissue concentrations were 1.52, 3.24, and 193.2 mg/kg tungsten
for the 10, 100, and 10,000 mg W/kg soil concentrations, respectively.

Test with aged soil
-The results of the second test are consistent with the results of the first test where all worms survived the 14-days exposure to soils amended with 10-1000 mg W/kg soil and all of them died at the 10,000 mg W/kg soil level.
- Tissue concentrations of 3.45 to 25.9 mg tungsten/kg dry weight were observed for tungsten soil concentrations ranging from 10 to 1000 mg/kg, respectively.

Conclusions:

Worms took up and accumulated tungsten in their tissue. Dry weight tissue concentrations were 1.52, 3.24, and 193.2 mg/kg tungsten
for the 10, 100, and 10,000 mg W/kg soil concentrations, respectively, in the test with unaged soils. In the test with tungsten-aged soil, tissue concentrations of 3.45 to 25.9 mg tungsten/kg dry weight were observed for tungsten soil concentrations ranging from 10 to 1000 mg/kg, respectively.

Executive summary:

No terrestrial bioaccumulation data of sufficient quality are available for tungsten carbide (target substance). However, terrestrial bioaccumulation data are available for tungsten metal (source substance), which are for read-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 on Annex 3 in the CSR.

Reference 2

Endpoint:

bioaccumulation: terrestrial

Type of information:

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

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well documented study, with accumulation results obtained during toxicity testing.

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: Tungsten metal
Target: Tungsten carbide
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

Principles of method if other than guideline:

Accumulation of tungsten in plant tissues obtained during toxicity testing.

GLP compliance:

not specified

Radiolabelling:

no

Details on sampling:

-Leaves were harvested several times over the 9 month vegetation period

Vehicle:

no

Details on preparation and application of test substrate:

- Method of mixing into soil (if used): Manually mixed with powder in different proportions to acheive metal concentrations ranging from 0.0001% to 10% on a mass basis.
- Controls: Non-amended urban soil

Test organisms (species):

other: Ryegrass

Details on test organisms:

- Common name: Ryegrass
- Plant family: Poaceae
- Source of seed: Ward's Biology (Rochester, NY)

Total exposure / uptake duration:

ca. 36 wk

Test temperature:

20 °C or room temperature (not specified)

pH:

No data

TOC:

urban: 5.3%

Moisture:

35%

Details on test conditions:

TEST SYSTEM
- Test container (type, material, size): Plastic jars
- Amount of soil: 100-200 g (held constant within each experiment)
- No. of seeds per container: 5
- No. of replicates per treatment group: three
- No. of replicates per control: Not specified

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographic location: urban soil (Stevens Institute of Technology campus, Hoboken, NJ, USA)
- Pesticide use history at the collection site: Not specified
- Sampling depth (cm): 1-5 cm
- Pretreatment of soil: Homogenized, large particles and plant roots removed, sieved through a 1 mm sieve.
- Storage (condition, duration): Stored at 4°C until use.

GROWTH CONDITIONS
- Photoperiod: 12/12 or natural light (held constant within each experiment)
- Light source: no data
- Light intensity and quality: no data
- Day/night temperatures: no data
- Watering regime and schedules: daily
- Water source/type: DI water
- Volume applied: 15 g/ day


EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Growth and tungsten concentration in plant tissue.

VEHICLE CONTROL PERFORMED: no

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10x

Nominal and measured concentrations:

0.1-10000 mg W/kg soil

Key result

Type:

BCF

Value:

>= 0.2 - <= 56.7 dimensionless

Basis:

other: whole plant

Time of plateau:

12 wk

Calculation basis:

steady state

Kinetic parameters:

No data

Metabolites:

No data

Details on results:

-Mean concentrations of W in ryegrass leaves (mg/kg) after 9 months were 5.67, 9.13, 10.5, 42.2, 201.7, and 13,535* corresponding to W concentrations in soil (mg/kg) of 0.1, 1.0, 10, 100, 1000, and 10,000; respectively. The 13,535 mg/kg level was obtained after only two months due to die off after this time point at this exposure level.
-The W uptake for the highest W concentration in soil was 13500 mg/kg (standard deviation 6100 mg/kg). These plants died off after 2 months of
incubation.
-Most significant uptake of tungsten by plants occurs at concentrations greater than 1000 mg/kg.

Conclusions:

Mean concentrations of W in ryegrass leaves (mg/kg) were 5.67, 9.13, 10.5, 42.2, 201.7, and 13,535 corresponding to W concentrations in soil (mg/kg) of 0.1, 1.0, 10, 100, 1000, and 10,000; respectively. Ryegrass takes up signiifcant amounts of tungsten from the soil over a 9 month period at high soil W concentrations.

Executive summary:

No terrestrial bioaccumulation data of sufficient quality are available for tungsten carbide (target substance). However, terrestrial bioaccumulation data are available for tungsten metal (source substance), which are used for read-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 on Annex 3 in the CSR.

Description of key information

Relatively low bioaccumulation of tungsten is observed in sunflower leaves at soil concentrations of 3900 mg W/kg soil, with calculated concentration factors plateauing at approximately 0.05 (Johnson et al, 2009). Tungsten concentrations factors calculated for ryegrass were higher and ranged from 56.1-0.202 (Strigul et al, 2005). However, it should be noted that background levels of tungsten in the collected soils used for testing were not determined prior to testing. Tungsten concentrations measured in earthworm tissue ranged from 1.52-193.2 mg/kg wet weight in soils with tungsten concentrations of 10-10000 mg/kg soil, respectively (non-aged soil) (Strigul et al, 2005). Additionally, tungsten concentrations of 10 and 10000 mg/kg soil yielded earthworm tissue concentrations of 3.45 and 25.9 mg/kg wet weight, respectively (Strigul et al, 2005). Using these paired concentration data the BCFs for earthworms in non-aged soils ranged 0.152-0.019 and BCFs for aged soils ranged 0.345-0.00259. However, it should be noted that background levels of tungsten in the collected soils used for testing were not determined prior to testing. Tungsten is not expected to bioaccumulate in terrestrial organisms.

Key value for chemical safety assessment

BCF (terrestrial species):

0.152 dimensionless