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REACH

Tungsten hexachloride

EC number: 236-293-9 | CAS number: 13283-01-7

Life Cycle description
Uses advised against

Environmental fate & pathways

Adsorption / desorption

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference 1

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

yes

Remarks:

-detailed characterization of the test substance was not provided

GLP compliance:

not specified

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

Test temperature:

25 °C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: high (5 mg/L, nominal) and low (1 mg/L)
- Sampling interval: after 3 week contact time
- Sample storage before analysis: no data

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: Eglin Airforce Base, Florida
- Collection procedures: no data
- Sampling depth (cm): no data
- Storage conditions: no data
- Storage length: no data
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): no data

PROPERTIES OF SOIL MATRICES
The two soil types used were designated as "sand" and "clay". The "sand" sample was collected from the upper layer (A-horizon) of the Lakeland series soil. The "clay" soil sample was collected from the sandy clay loam sub surface layer (Bt-horizon) of the Lucy series. The Lakeland series "sand" soil was generally light tan in color. Quartz grains of sand size were the main component of the Lakeland series sample. These grains were sparingly coated by clays. The sample also contained approximately 1% organic fragments. The Lucy series soil was also dominated by quartz grains but these grains had more extensive clay coatings colored red by iron oxides.

PROPERTIES OF WATER MATRICES
Three types of artificial waters were used in the experiments: surface water, groundwater, and sea water.
See Table 1 in other information on Materials and Methods section for water characterization.

Details on test conditions:

TEST CONDITIONS
- pH: 4.5, 6.5, and 8.5
- Suspended solids concentration: no data

TEST SYSTEM
- Type, size and further details on reaction vessel: no data
- Water filtered (i.e. yes/no; type of size of filter used, if any): yes, no data
- Amount of soil/sediment/sludge and water per treatment (if simulation test): no data
- Soil/sediment/sludge-water ratio (if simulation test): no data
- Number of reaction vessels/concentration: one (per set of unique conditions)
- Measuring equipment: no data
- Method of preparation of test solution: metals were dissolved in the water matrices and then contacted with soil
- Other: The samples were periodically agitated to ensure equilibration of metals with soil. After a contact time of three weekes, the water was separated from the soil, filtered, and prepared for metal analysis.

Computational methods:

Scatter plots of Kd versus pH were used to evaluate the characteristic trends of each metal in different environments.

Sample No.:

Phase system:

soil-water

Type:

Remarks:

Value:

>= 100 - <= 31 600 dimensionless

Temp.:

25 °C

pH:

4.5

Matrix:

sand, clay

% Org. carbon:

ca. 1

Sample No.:

Phase system:

soil-water

Type:

Remarks:

Value:

>= 10 - <= 3 160 dimensionless

Temp.:

25 °C

pH:

6.5

Matrix:

sand, clay

% Org. carbon:

ca. 1

Sample No.:

Phase system:

soil-water

Type:

Remarks:

Value:

>= 3.16 - <= 100 dimensionless

Temp.:

25 °C

pH:

8.5

Matrix:

sand, clay

% Org. carbon:

ca. 1

Adsorption and desorption constants:

The Kds for tungsten increased with decreasing pH. At pH 4.5 Kd values ranged approximately from 100-31,600; at pH 6.5 Kd values ranged from approximately from 10-3160; and at pH 8.5 Kd values ranged approximately from 3.16-100 (values presented in figure format in study).

In general, the trend for Kds as related to water type was as follows for tungsten: Kd(suface water)> Kd(ground water)>Kd(sea water), regardless of pH.

In general, the trend for Kds as related to soil type was as follows for tungsten: Kd(clay)> Kd(sand), regradless of pH.

There was no clear relationship between the intial metal concentration and the sorption coefficient over the concentration ranges tested, which may indicate that the range of initial metal concentrations tested falls on the linear part of the adsorption isotherm.

It should be noted that at Kd values greater than 100, the differences in values were significantly affected by the error in the analysis of the ver small concentration of metals remaining in solution.

Recovery of test material:

No data

Concentration of test substance at end of adsorption equilibration period:

Not explicitly provided

Concentration of test substance at end of desorption equilibration period:

Not applicable

Validity criteria fulfilled:

not applicable

Conclusions:

The Kds for tungsten increased with decreasing pH.

Executive summary:

A study similar to OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method) was conducted with tungsten at nominal concentrations of 1 mg/l and 5 mg/L. Sampling was conducted after 3 week contact time. The two soil types used were designated as "sand" and "clay". Three types of artificial waters were used in the experiments: surface water, groundwater, and sea water. The test was conducted at pH 4.5, 6.5, and 8.5.

As a result the Kd values for tungsten increased with decreasing pH. At pH 4.5 Kd values ranged approximately from 100-31,600; at pH 6.5 Kd values ranged from approximately from 10-3160; and at pH 8.5 Kd values ranged approximately from 3.16-100.

Reference 2

Endpoint:

adsorption / desorption

Remarks:

adsorption

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

In this study, solubilization and sorption of various tungstate species with a model soil was investigated in four sets of experiments. All leachates were processed through a 0.45 µm filter to obtain dissolved constituents and removed suspended soil particles.

In the first set of experiment, to determine the effect of polymerization on sorption and thus dissolved phase concentrations, the partition coefficients for four commercially available tungsten compounds (sodium tungstate dihydrate, sodium phosphotungstate, sodium polytungstate, and tungstosilicic acid n-hydrate) on clean test soil in deionized water matrix were determined. All sorption partition coefficient studies had a minimum equilibration time of 3 days, with some experiments performed to 4 months.

In a second experiment, the effects of pH, phosphate (at various pH values), ionic strength, and humic acid on the tungstate Kd value were determined after an equilibration of 14-days.

In a third experiment, partition coefficients for the two most abundant metal oxides in the Grenada Loring soil (Al and Fe) were determined to elucidate tungstate’s affinity for pure metal oxides.

In order to examine the affect of soil-aging on the speciation of extractable, soluble tungsten compounds a fourth experiment was performed. In this experiment, the leachate obtained from extracting tungsten metal-spiked soil, after the soil had been aged for one year, with deionized water for 168 hrs. The leachate solution was then used as the spike solution for clean Grenada Loring soil to determine the effective partitioning for the tungsten species (undetermined) extractable from the soil.

GLP compliance:

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

- Name of test material (as cited in study report): Na2WO4.2H2O

Radiolabelling:

Analytical monitoring:

yes

Details on sampling:

- Sampling interval: equilibration times of 3 days or 4 months
- Sampling storage: up to 1 year
- Sample storage before analysis: no data

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: Grenada Loring Soil was collected from the Brown Loam Experimental Station (Learned, MS)
- Collection procedures: The silty loam soil was collected with a front-end loader after the top 12 cm were removed to eliminate unwanted vegetation.
- Sampling depth (cm): > 12 cm
- Storage conditions: no data
- Soil preparation: < 1 cm sieved

PROPERTIES
- Soil texture
- % sand: 3
- % silt: 72
- % clay: 26
- Horizon: no data
- Soil taxonomic classification: no data
- Soil classification system: no data
- Soil series: no data
- Soil order: no data
- pH: 6.7
- Organic carbon (%): 0.7
- CEC (meq/g): 0.075 (cation), 0.025 (anion)
- Carbonate as CaCO3: no data
- Insoluble carbonates (%): no data
- Extractable Cations: no data
- Special chemical/mineralogical features: no data
- Clay fraction mineralogy: no data
- Moisture at 1/3 atm (%): no data
- Bulk density (g/cm3): no data
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): no data

Details on test conditions:

TEST CONDITIONS
- Buffer: no data
- pH: no data
- Suspended solids concentration: no data
- Other: no data

TEST SYSTEM
- Type, size and further details on reaction vessel: no data
- Measuring equipment: Tungstate analysis was performed using an Agilent (Palo Alto, CA) 1100 HPLC interfaced to the PerkinElmer Elan 6000 ICP–MS with a cross-flow pneumatic nebulizer.
- Test performed in closed vessels due to significant volatility of test substance: no
- Test performed in open system: yes

Computational methods:

The Kd values were determined following the linear Freundlich model with associated linear fit correlation.

Adsorption and desorption constants:

Adsorption coefficient (Kd) for tungstate in non-aged soil, extraction with deionized water:
3 d: 284 L/kg
4 mo: 845 L/kg

Details on results (Batch equilibrium method):

In the experiment designed to examine the effects of tungstate polymerization on the Kd value, tungstate showed a marked increase in Kd values over the 4 month study, (Kd 3 days= 284 L/kg; Kd 100 days = 845 L/kg) suggesting that it interacts with the soil to become less mobile with time, either through precipitation or sorption mechanisms or further changes in speciation. Kds for the other compounds tested were lower with the 3-day and 100-day Kds ranging from 92-112 L/kg and 97-500 L/kg, respectively. In the experiment designed to examine the effects of tungstate polymerization on the Kd value, phosphotungstate showed a marked increase in Kd values over the 4 month study (112 and 500 L/kg at 3 d and 4 mo, respectively), suggesting it interacts with the soil to become less mobile with time, either through precipitation or sorption mechanisms or further changes in speciation. The polytungstate and tungstosilicate compound Kd values remained relatively unchanged over the 4-month Kd study (92 and 135 L/kg and 103 and 97 L/kg for polytungstate and tungstosilicate at 3 d and 4 mo, respectively), suggesting that they do not undergo significant geochemical changes in this system over the time period studied.

In the second experiment, which determined the effects of pH, phosphate, ionic strength and humic acid content on the tungstate Kd, the data suggest that increased pH (either from sodium hydroxide or phosphate, both at pH = 11) decreased the Kd value (the Kd values at pH 3, 7 and 11 were 414, 141, and 62 L/kg, respectively, compared to 673 L/kg for deionized water), as would be expected with an anionic compound (i.e. surface exchange sites become negatively charged). Humic acid and sodium sulfate as concomitant compounds had little effect on tungstate Kd values in comparison to the deionized water system (863 L/kg for Na2SO4 pH=7.0, and 749 L/kg for 10 mg/L humic acid). This was likely due to the fact that tungstate has a higher affinity for sorption sites than these compounds, which may not be the case with phosphate, or the humic substance behaves as a surfactant to the soil particle surface. Additionally, substantial amounts of naturally occurring salts will dissolve from the soil into the deionized water system, essentially making the ionic strength of the deionized water system similar to the sodium sulfate and humic acid matrices. Because the Grenada Loring soil has substantial amounts of oxide-forming metals (1.1% Al, 1.5% Fe 0.06% Mn), it is likely that some combination of these phases will influence tungsten sorption processes.

In order to elucidate tungsten's affinity for pure metal oxides, the Kd values were obtained for the most abundant metal oxides in the soil. Aluminum and iron (III) oxides have tungstate Kd values of approximately 1970 and 1780 L/kg, respectively, using the same procedure previously described for the soil experiments. In comparison, arsenic oxyanion compounds have partition coefficients on freshly precipitated aluminum, iron, and manganese oxyhydroxides that range from <1 to over 200 L/kg depending on pH conditions, suggesting tungstate sorption to metal oxide phases will be extensive in this system.

The the overall Kd value for all dissolved, extractable tungsten species obtained using leachate from the extraction of aged, tungsten-metal spiked soil, after 3 days of equilibration was 110 L/kg (R2 = 0.98), which is almost a factor of 3 lower than the value obtained for tungstate, but close to the values obtained for polytungstate and tungstosilicate 284 L/kg for tungstate, 92 L/kg for polytungstate, and 103 L/kg for tungstosilicate) obtained in the first set of experiments. The Kd value measured for the geochemical form of tungstate in the tungsten spiked soil closely matches those of commercially available polymer tungsten compounds, indicating that a large portion of soluble tungsten in the Grenada Loring soil exists as polymeric species.

Elemental analysis of the soil yielded the following concentrations in mg/kg: aluminum (10,900); barium (81); calcium (925); iron (14,900); potassium (778); magnesium (1336); manganese (660); sodium (85); phosphorous (455); sulfur (172); titanium (37); and tungsten (12). In the tungsten metal-spiked soil the tungsten content was 7080 mg/kg.

Validity criteria fulfilled:

not applicable

Conclusions:

When extracted in deionized water, the mobility of tungstate in the soil decreased from 3 days to 4 months with Kd values increasing from 284 to 845 L/kg. Kd values of tungstate (measured after 14-days) decreased with increasing pH with values of 414, 141 and 62 L/kg at pH 3.0, 7.0 and 11.0; however, in the presence of sodium sulfate and humic acid the Kd values were similar to that obtained for deionized water (673 L/kg), 863 and 749 L/kg, respectively, likely due to the fact that tungstate has a higher affinity for sorption sites than these compounds. For the tungsten species extracted from the tungsten metal-spiked soil that had aged for 1 year, the overall Kd value obtained after 3 days of equilibration was 110 L/kg.

Executive summary:

Solubilization and sorption of tungstate species with a model soil was investigated in four sets of experiments. All leachates were processed through a 0.45-µm filter to obtain dissolved constituents and removed suspended soil particles.

Tungsten-containing soil was created by adding metallic tungsten (<1-μm particles) to a Grenada Loring soil (test soil), mixing, and allowing it to age in plastic drums at ambient outdoor conditions for up to 1 year.

To determine the effect of polymerization on sorption and thus dissolved phase concentrations, the partition coefficients of for four commercially available tungsten compounds (sodium tungstate dihydrate, sodium phosphotungstate, sodium polytungstate, and tungstosilicic acid n-hydrate) on the clean Grenada Loring soil in deionized water matrix were determined. All sorption partition coefficient studies had a minimum equilibration time of 3 days, with some experiments performed to 4 months.

In a second experiment, the effects of pH, phosphate (at various pH values), ionic strength, and humic acid on the tungstate Kd value were determined.

Since the Grenada Loring Soil has substantial amounts of oxide-forming metals (1.1% Al, 1.5% Fe, 0.06% Mn), it is likely that some combination of these phases will influence tungsten sorption processes; therefore, in a third experiment, partition coefficients for the two most abundant metal oxides in the Grenada Loring soil (Al and Fe) were determined to elucidate tungstate’s affinity for pure metal oxides.

In the fourth experiment, a partition coefficient experiment was performed using the tungsten species extracted from tungsten-spiked soil (spiked with tungsten metal) after the soil had aged for 1 year. For this test, the tungsten soil was extracted with deionized water for 168 h. The leachate was then filtered and analyzed for dissolved tungsten (~150 mg/L). This solution was then used as the spike solution for clean Grenada Loring soil to determine the partition coefficient for the tungsten species extractable from the soil.

As a result, when extracted in deionized water, the mobility of tungstate in the soil decreased from 3 days to 4 months with Kd values increasing from 284 to 845 L/kg. Kd values of tungstate (measured after 14-days) decreased with increasing pH with values of 414, 141 and 62 L/kg at pH 3.0, 7.0 and 11.0; however, in the presence of sodium sulfate and humic acid the Kd values were similar to that obtained for deionized water (673 L/kg), 863 and 749 L/kg, respectively, likely due to the fact that tungstate has a higher affinity for sorption sites than these compounds. For the tungsten species extracted from the tungsten metal-spiked soil that had aged for 1 year, the overall Kd value obtained after 3 days of equilibration was 110 L/kg.

Reference 3

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

yes

Remarks:

: 1) CaCl2 solution not used; 2)samples were settled gravimetrically and not by centrifugation

GLP compliance:

Remarks:

Information from scientiifc research; scientific research is usually not conducted under GLP.

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

- Name of test material (as cited in study report): sodium tungstate dihydrate, CAS 10213-10-2

Radiolabelling:

Test temperature:

no data

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 5, 10, 15, 20, 25, 50, 75, 100, 150 and 200 mg metal/L
- Sampling interval: 1, 20, 40, 60, 80 and 100 days
- Sample storage before analysis: no data

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: no data
- Collection procedures: no data
- Sampling depth (cm): no data
- Storage conditions: no data
- Storage length: no data
- Soil preparation: no data

PROPERTIES
- Soil texture
- % sand: 81.9, 90.40 and 77.20 for soils SM(1), SM(2) and SM(3), respectively
- % silt: 18.10, 9.60 and 22.30 for soils SM(1), SM(2) and SM(3), respectively
- % clay: no data
- Horizon: no data
- Soil taxonomic classification: no data
- Soil classification system: no data
- Soil series: no data
- Soil order: no data
- pH: 5.74, 4.85 and 5.50 for soils SM(1), SM(2) and SM(3), respectively
- Organic carbon (%): 0.89, 0.57 and 0.83 for soils SM(1), SM(2) and SM(3), respectively
- CEC (meq/100 g): 4.50, 4.30 and 6.50 for soils SM(1), SM(2) and SM(3), respectively
- AEC (meq/100 g): 5.03, 2.69 and 4.25 for soils SM(1), SM(2) and SM(3), respectively
-BET surface area: 2.30, 1.98, and 2.80 for soils SM(1), SM(2) and SM(3), respectively
- Carbonate as CaCO3: no data
- Insoluble carbonates (%): no data
- Extractable Cations (Ca, Mg, Na, K, H): no data
- Special chemical/mineralogical features: no data
- Clay fraction mineralogy: no data
- Moisture at 1/3 atm (%): no data
- Bulk density (g/cm3): no data
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): no data.

Details on test conditions:

TEST CONDITIONS
- Buffer: no data
- pH: no data
- Suspended solids concentration: no data
- Other: no data

TEST SYSTEM
- Type, size and further details on reaction vessel: no data
- Water filtered: no data
- Number of reaction vessels/concentration: 3
- Are the residues from the adsorption phase used for desorption: no

Computational methods:

- Adsorption and desorption coefficients (Kd): no data
- Freundlich adsorption and desorption coefficients: no data
- Slope of Freundlich adsorption/desorption isotherms: no data
- Adsorption coefficient per organic carbon (Koc): no data
- Regression coefficient of Freundlich equation: yes, these correlation coefficients were generated
- Other: A least squares fit was performed to determine the sorptive parameters of each soil-metal system according to the power law relation: Cs = KdCw^(1/n), where Kd is the distribution coefficient, and n is a constant specific to the soil-metal system. For each soil-metal system, the distribution coefficient and exponent were determined by nonlinear regression according to the Marquardt-Levenberg algorithm, using the software package Sig-maplot.

Sample No.:

Type:

Value:

16.6 dimensionless

Matrix:

SM1

Remarks on result:

other: Result of day 1

Sample No.:

Type:

Value:

325.8 dimensionless

Matrix:

SM1

Remarks on result:

other: Result of day 100

Sample No.:

Type:

Value:

27.1 dimensionless

Matrix:

SM2

Remarks on result:

other: Result of day 1

Sample No.:

Type:

Value:

167.9 dimensionless

Matrix:

SM2

Remarks on result:

other: Result of day 100

Sample No.:

Type:

Value:

75.8 dimensionless

Matrix:

SM3

Remarks on result:

other: Result of day 1

Sample No.:

Type:

Value:

181.8 dimensionless

Matrix:

SM3

Remarks on result:

other: Result of day 100

Adsorption and desorption constants:

SM1: Kd 1-day = 16.6 ± 2.1; Kd 100-day = 325.8 ± 20.6
SM2: Kd 1-day = 27.1 ± 5.5; Kd 100-day = 167.9 ± 8.7
SM3: Kd 1-day = 75.8 ± 5.5; Kd 100-day = 181.8 ± 13.5

Soil	Equilibration	Kd(including 95% CI)	*n (including 95% CI)**	Freundlichisotherm R²	Kd¹⁰⁰/Kd¹
SM1	1 day	16.6 ± 2.1	2.11 ± 0.11	0.9551	19.6
	100 days	325.8 ± 20.6	2.87 ± 0.14	0.97
SM2	1 day	27.1 ± 5.5	3.18 ± 0.40	0.736	6.2
	100 days	167.9 ± 8.7	2.85 ± 0.10	0.9854
SM3	1 day	75.8 ± 5.5	2.79 ± 0.12	0.9722	2.4
	100 days	181.8 ± 13.5	3.91 ± 0.26	0.9374

Table 1. Freundlich distribution coefficients and exponents for three soil-tungsten systems

Tungsten Kd100 results indicate that in some systems a longer equilibration time will produce a Kd that more closely predicts the behavior of the metals in the soil under equilibrium conditions. In this case, large increases in the distribution coefficient were observed between one and 100 days. The ratios of Day 100 to Day 1 distribution coefficients were 19.6, 6.2 and 2.4 for tungsten in SM1, SM2 and SM3, respectively.

For each of the soil–tungsten systems studied the 20-day distribution coefficient is significantly greater than the one-day distribution coefficient (>95 % confidence). Following a 100-day equilibration, the observed distribution coefficients are not significantly greater than the 80-day distribution coefficient (Kd 80), though the Kd 100 is significantly (>95 % confidence) greater than the Kd 60. This indicates that equilibrium may have been reached by the 100-day mark, but not before.

Validity criteria fulfilled:

not applicable

Conclusions:

Tungsten requires a long stabilization period, as evidenced by the comparison of Freundlich distribution coefficients over a 100-day period.

Executive summary:

In a study similar to OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method) sodium tungstate dehydrate was used in concentrations of 5, 10, 15, 20, 25, 50, 75, 100, 150 and 200 mg metal/L in three natural silty sand soils (SM(1), SM(2) and SM(3)) to identify the sorption characteristics associated with tungsten. Partitioning coefficients were obtained both at the traditional 24-hour contact time (Kd1) and again after 100 days (Kd100).

To determine the Kd values of tungsten–soil systems, initial batch slurries were prepared using 10 g of soil and 100 mL of sodium tungstate, respectively. Soil–metal systems were prepared in triplicate using each of three natural silty sand soils (SM1, SM2, SM3), and each of ten stock concentrations. The batch slurries were placed on a shaker table, agitated for 24 hours, and allowed to settle for ten minutes. A sub-sample of supernatant was removed and analyzed for total tungsten or lead content. The directly determined aqueous concentrations were then used to calculate the total sorbed concentration of metal in the system.

The batch slurries were returned to the shaker table, and additional sub-samples were collected from the systems at 100 days to obtain the Kd 100 values. Samples were taken at 1, 20, 40, 60, 80 and 100 days to observe equilibrium kinetics. Control experiments were performed to eliminate artificial adsorption phenomena such as adsorption to container surfaces and precipitation.

Resulting adsorption constants are as follows:

SM1: Kd 1-day = 16.6 ± 2.1; Kd 100-day = 325.8 ± 20.6

SM2: Kd 1-day = 27.1 ± 5.5; Kd 100-day = 167.9 ± 8.7

SM3: Kd 1-day = 75.8 ± 5.5; Kd 100-day = 181.8 ± 13.5

A comparison of Freundlich distribution coefficients over a 100-day period demonstrates that tungsten requires a long stabilization period.

Reference 4

Endpoint:

adsorption / desorption, other

Remarks:

partitioning in the environment

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

The sampling process was well documented and sampling, metal analysis, and media characterization was orchestrated under scientifically sound principles. No data on the behavior of tungsten dioxide in the environment are available. Adsorption data for tungsten metal are appropriate for read-across for this endpoint as the soluble species released are expected to be similar for each of the compounds, and are thus expected to behave similarly in the environment. For more details refer to the attached description of the read across approach.

Principles of method if other than guideline:

Tungsten partition coefficients for water-sediment were derived using paired environmental monitoring samples of tungsten in water and sediment collected in various parts of the EU.

GLP compliance:

Type of method:

other: adsorption desorption based on paired sediment-water samples

Media:

sediment

Radiolabelling:

Test temperature:

Ambient temperature

Details on sampling:

- 875 samples taken
- Each stream sediment sample was comprised of material taken from 5-10 points over a stretch of 250-500 m along the stream.
- Sites were located at least 100 m upstream of roads and settlements.
- Sampling was started from the stream water sampling point, and the other sub-samples were collected up-stream. A composite sediment sample was made from sub-samples taken from beds of similar nature.
- Running stream water was collected from the small, second order, drainage basins (<100 km2) at the same site as the stream sediment.
- In dry terrain, such as Southern Europe, streams had no running water for most of the year. Hence, the sampling, whenever possible, was carried out during the winter and early spring months.
- Sub-samples of stream water were separately collected from each site: unfiltered water for major IC ion analysis, filtered water (0.45 μm) for ICP-MS and ICP-AES analysis, and DOC analysis.
- Sampling during rainy periods and flood events was avoided. The water sample was collected from the first, lowermost stream sediment sampling point.
- The pH and EC were measured, and alkalinity estimated by titration at the site.

Phase system: