Tungsten carbide

Bioaccumulation: aquatic / sediment

Link to relevant study record(s)

Reference

Endpoint:

bioaccumulation in aquatic species: fish

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

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 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

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OPP 72-6 (Aquatic Organism Accumulation Tests)

GLP compliance:

not specified

Remarks:

Research conducted by Center for Environmental Systems, Stevens Institute of Tec hnology, Castle Point on Hudson, Hoboken, NJ 07030, USA

Specific details on test material used for the study:

Sodium tungstate powder was obtained as the hydrate, Na2WO4 2H2O.

Radiolabelling:

no

Vehicle:

no

Test organisms (species):

Poecilia reticulata

Details on test organisms:

Guppies (Poecilia reticulate) were obtained from Ward’s Natural Science. Special attention was paid to provide healthy fish for the test and to reduce possible biases. After arriving, fish were kept for at least 4 weeks in the fish tanks (50 L) under constant temperature (23±1°C) to evaluate whether they were healthy enough to be used in the experiments and to acclimate the fish to the local tap water.

Route of exposure:

aqueous

Test type:

other: Static-Renewal

Water / sediment media type:

natural water: freshwater

Test temperature:

Water temperature was 23.5 ± 0.3°C

pH:

pH between 7.43 and 8.1 (sodium tungstate slightly increased water pH, from 7.4 to 8.02)

Dissolved oxygen:

Dissolved oxygen varied between 3.7 and 5.49 mg/L. Sodium tungstate decreased dissolved oxygen concentration (down to 3.7 mg/L).

Conductivity:

Water conductivity in the range 0.399–5.29 mS/cm.

Details on test conditions:

Ammonia concentration was lower than the detection limit (0.01 mg/L.), nitrates and nitrites did not statistically differ between the control tanks and experimental tanks and the concentrations did not exceed 5 and 0.1 mg/L, respectively. Redox potential between 265 and 291 mV. Sodium tungstate decreased redox potential (from 295 to 265 mV), and wWhile these changes are in agreement with water chemistry theory and somewhat expected, none of them were deemed significant enough to cause fish mortality.

Nominal and measured concentrations:

Animals were exposed to seven distinct concentrations of sodium tungstate and sodium metatungstate (9, 7.5, 5, 3.75, 2.5, 2.5, 0.75 g (Na2WO4 2H2O) L.

Reference substance (positive control):

no

Details on estimation of bioconcentration:

Tungsten uptake was measured in 10 fish used in experiments including 4 fish from control groups and 6 fish that were exposedto tungsten. Dead fish were washed in DI-water, weighed, then dried for 12 h in an oven at 80°C. Dried fish were weighed, chopped and placed in 50 mL digestion vials along with HNO3 (5 mL), HCl (1 mL), H3PO4 (0.5 mL), and H2O2 (3 mL). The vials were open heated in a heating block under the hood for 2 h at 180°C; up to 3 mL H2O2 were added during the digestion to compensate evaporation losses. Subsequently, samples were allowed to cool down, filtered through a Whatman 42 paper, and diluted to 50 mL with DI-water. Finally tungsten concentration in samples was measured by inductively coupled plasmaoptical emission spectroscopy (ICP-OES, wavelength 207.911 nm) calibrated up to 1 mg/mL W with the tungsten atomic absorption standard solution.

Tungsten bioconcentration factors (BCF) were calculated as the ratio between tungsten concentration in fish tissues (expressed in mg of W per kg of wet or dry tissue) to tungsten concentration in water (expressed in mg/L).

Key result

Conc. / dose:

ca. 7.5 g/L

Temp.:

> 23.2 - < 23.8 °C

pH:

7.2

Type:

BCF

Value:

> 0 - < 1.23 L/kg

Basis:

whole body w.w.

Remarks:

0.29 ± 0.94 L/Kg

Time of plateau:

24 h

Calculation basis:

steady state

Key result

Conc. / dose:

ca. 7.5 g/L

Temp.:

> 23.2 - < 23.8 °C

pH:

7.2

Type:

BCF

Value:

> 1.07 - < 2.07 L/kg

Basis:

whole body d.w.

Remarks:

1.57 ± 0.5 L/kg

Time of plateau:

24 h

Calculation basis:

steady state

Details on results:

Fish (3 per each tested chemical) died during the first 24 h after they were exposed to 7.5 g/L of sodium tungstate. The average tungsten concentrations in fish are 1230±390, and 30 ±2 mg of W per kg of fish, for sodium tungstate, and control fish, respectively. BCF for sodium tungstate are 0.29±0.94 and 1.57±0.5 L/kg.where the first coefficient has been calculated using the wet fish weight and the second number is for the dry fish weight.

Validity criteria fulfilled:

yes

Conclusions:

BCF for sodium tungstate are 0.29±0.94 and 1.57±0.5 L/kg.where the first coefficient has been calculated using the wet fish weight and the second number is for the dry fish weight. Sodium tungstate has a low potential for bioconcentration in freshwater fish.

Executive summary:

No aquatic bioaccumulation data of sufficient quality are available for tungsten carbide (target substance). However, 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 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 on Annex 3 in the CSR. 

Description of key information

No information on the bioconcentration or accumulation in aquatic organisms was found for tungsten carbide. However, data were available for sodium tungstate which was used for read-across. In a static renewal, toxicity test on Poecilia reticulatetesting sodium tungstate, Strigul et al (2010) measured tungsten uptake in 5 fish-2 controls, 3 exposed to 7.5 g/L (nominal sodium tungstate concentration). The fish from the test group had died within the first 24 hours of exposure. BCF was calculated as the ratio of tungsten concentration in fish tissue (in mg W per kg wet or dry) to tungsten concentration in water (in mg/L). The BCF was calculated on both wet and dry weight of fish. Wet weight BCF for the test substance was calculated as 0.29 +/- 0.94 L/kg. Dry weight BCF for the test substance was calculated as 1.57 +/- 0.5 L/kg. These BCFs are low, indicating little to no immediate accumulation even at toxic exposure levels.

Key value for chemical safety assessment

BCF (aquatic species):

0.29 L/kg ww