Tungsten dioxide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

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

Adequacy of study:

key study

Study period:

2009-01-28 To: 2009-06

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The bioaccessability study described in this report was performed according to the "Draft Guidance for RIP 3.6: Bioavailability and Read-Across for Metals and Minerals". GLP study. Well documented, scientifically sound study. The reliability of this study for the substances 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. The data of the study serve as basis for the applied read-across approach.

Justification for type of information:

1. HYPOTHESIS FOR THE CATGEORY 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 Trioxide
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

Objective of study:

absorption

Qualifier:

according to guideline

Guideline:

other: Draft Guidance for RIP 3.6: Bioavailability and Read-Across for Metals and Minerals

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Species:

other: Human simulated fluids

Strain:

not specified

Sex:

not specified

Details on test animals or test system and environmental conditions:

no data

Route of administration:

other: In vitro study

Details on exposure:

Preparation of Testing Fluids: The simulated fluids used in this study were gastric, lung alveolar, lung interstitial, lysosomal and artificial sweat. All salts and reagents used for the simulated fluid preparation were obtained from Sigma-Aldrich (St. Louis, MO).

Extraction Experiments: Extractions of the test substances in the simulated fluids were performed at pre-set time periods (up to 72 hours) while protected from light, using 0.1 g of sample in 50 ml of simulated fluid, at 37 C and with continuous shaking (for all fluids except sweat, for which only initial shaking was performed). The experiments were carried out as follows:
- Simulated Gastric Fluid: The reactions were sampled for the determination of tungsten at 5 hours.
- Simulated Interstitial, Alveolar and Lysosomal Fluids: 5% CO2 in nitrogen was bubbled into solution at a rate of 50 ml/min. The reactions were sampled for the determination of tungsten at 2, 5, 24, and 72 hours.
- Simulated Sweat: The reactions were sampled for the determination of tungsten after 12 hours. No shaking was performed after the initial set up.

Sample Preparation: The simulated fluid extract samples were filtered immediately after sampling using 50 ml centrifuge tubes equipped with 0.45 microns PVDF filters (Grace Alltech, Deerfield, IL). The filtrates were stored in plastic bottles at 35 C until analysis.

The extracts were then analyzed for tungsten by inductively coupled plasma-mass spectrometry (ICP-MS).

Duration and frequency of treatment / exposure:

Single application of tungsten with fluids. Simulated Gastric Fluid was sampled for the determination of tungsten at 5 hours. Simulated Interstitial, Alveolar and Lysosomal Fluids were sampled for the determination of tungsten at 2, 5, 24, and 72 hours. Simulated Sweat was sampled for the determination of tungsten after 12 hours.

Remarks:

Doses / Concentrations:
0.1 g of test substance in 50 mL of simulated fluid

Control animals:

no

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: Simulated gastric fluid, Simulated interstitial fluid, Simulated alveolar fluid, Simulated lysosomal fluid and Simulated sweat
- Time and frequency of sampling: Simulated gastric fluid sampled at 5 hours, Simulated interstitial fluid sampled at 2, 5, 24, and 72 hours, Simulated alveolar fluid sampled at 2, 5, 24, and 72 hours, Simulated lysosomal fluid sampled at 2, 5, 24, and 72 hours and Simulated sweat sampled after 12 hours.

Sample analysis: Samples were diluted (if necessary), spiked with an internal standard [bismuth (Bi) at 1,000 pg/mL, prepared from dilution of a 1,000 ug/mL Certified Standard; Ultra Scientific, North Kingston, RI and analyzed directly on a Perkin Elmer Elan DRC II ICP-MS equipped with a dynamic reaction cell (DRC) and PerkinElmer AS-93 Plus autosampler instrument, according to methods established at IITRI for this study. A standard curve (prepared from dilutions of a 10,000 5%HNO3/6% HF; inorganic Ventures, Lakewood, NJ] was analyzed along with samples on each day of analysis. Instruments calibrators were prepared by diluting Certified Standard with 0.5% nitric acid to concentrations of approximately 200; 400; 800; 1,600; 3,200; 6,400; 13,000; and 25,000 pg/mL.

Statistics:

Calibration curves, regression coefficients and r-squared values were calculated using PerkinElmer ICP-MS software and Microsoft Excel software. Concentration values of tungsten in the study samples were calculated from linear regression coefficients derived from calibration standards that bracketed the expected concentration levels of tungsten in the study samples.

Details on absorption:

The fluid extracts were diluted 1:50 to 1:125000 for analysis. The average amount of tungsten found in the extracts was in the 0.0055 to 39% range. The maximum solubility was determined at 72 hours for the simulated alveolar, lysosomal and interstitial fluids (34, 38 and 39%, respectively). %RSDs ranged from 2.5 to 37%.

Toxicokinetic parameters:

other: not applicable

Gastric Fluid: The mean percent of available tungsten in simulated gastric fluid sampled at 5 hours was 0.0055 +/- 0.00026 % (4.7 % relative standard deviation). Sweat Fluid: The mean percent of available tungsten in simulated sweat fluid sampled at 12 hours was 7.9 +/- 1.3 % (17 % relative standard deviation). Alveolar Fluid: The mean percent of available tungsten in simulated alveolar fluid sampled at 2, 5, 24, and 72 hours was 2.4 +/- 0.18, 7.5 +/- 0.51, 18 +/- 2.5, and 34 +/- 6.1 %, respectively; the percent relative standard deviation for the 2, 5, 24, and 72 hours was 7.5, 6.8, 13 and 18 %RSD, respectively. Lysosomal Fluid: The mean percent of available tungsten in simulated lysosomal fluid sampled at 2, 5, 24, and 72 hours was 0.49 +/- 0.014, 1.3 +/- 0.032, 18 +/- 2.6, and 38 +/- 1.3 %, respectively; the percent relative standard deviation for the 2, 5, 24, and 72 hours was 2.8, 2.5, 15, and 3.5 %RSD, respectively. Interstitial Fluid: The mean percent of available tungsten in simulated interstitial fluid sampled at 2, 5, 24, and 72 hours was 2.3 +/- 0.83, 11 +/- 2.8, 23 +/- 4.3, and 39 +/- 1.6 %, respectively; the percent relative standard deviation for the 2, 5, 24, and 72 hours was 37, 25, 19, and 4.1 %RSD, respectively.

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
The bioavailability of tungsten trioxide was determine in artificail body fluids (simulated gastric, alveolar, lysosomal , and interstitial fluid). Solubility ranges form 0.0055% at pH 1.5 to 39 % in artificial interstitial fluid.

Executive summary:

In a GLP in vitro study conducted according to Draft Guidance for RIP 3.6: Bioavailability and Read-Across for Metals and Minerals, the bioavailability of tungsten trioxide was determine in human gastric, sweat, alveolar, lysosomal, and interstitial fluids. The mean percent of available tungsten in simulated gastric fluid sampled at 5 hours was 0.0055 % (4.7 % relative standard deviation). The mean percent of available tungsten in simulated sweat fluid sampled at 12 hours was 7.9 (17 % relative standard deviation). The mean percent of available tungsten in simulated alveolar fluid sampled at 2, 5, 24, and 72 hours was 2.4, 7.5, 18, and 34, respectively; the percent relative standard deviation for the 2, 5, 24, and 72 hours was 7.5, 6.8, 13 and 18 %RSD, respectively. The mean percent of available tungsten in simulated lysosomal fluid sampled at 2, 5, 24, and 72 hours was 0.49, 1.3, 18, and 38%, respectively; the percent relative standard deviation for the 2, 5, 24, and 72 hours was 2.8, 2.5, 15, and 3.5 %RSD, respectively. The mean percent of available tungsten in simulated interstitial fluid sampled at 2, 5, 24, and 72 hours was 2.3, 11, 23, and 39%, respectively; the percent relative standard deviation for the 2, 5, 24, and 72 hours was 37, 25, 19, and 4.1 %RSD, respectively. The bioavailability in the fluids ranged from 0.0055% (gastric fluid) to 39% (interstitial fluid). The maximum solubility was determined at 72 hours for the simulated alveolar, lysosomal and interstitial fluids (34, 38 and 39%, respectively). Based on the results, the bioavailability of tungsten trioxide would be expected to be low for the oral route of administration, but moderate for inhalation route.

These data are used for the read-across approach for tungsten dioxide.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

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

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well documented study with sufficient methods and results provided to accurately evaluate results. Due to similar physical-chemical properties, similar or lower transformation/dissolution results and similar or lower in vitro bioaccessibility in synthetic body fluids for tungsten dioxide (the target substance) than the source substances, 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: Tungsten Trioxide
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

Objective of study:

absorption

distribution

excretion

Qualifier:

no guideline followed

Principles of method if other than guideline:

Tissue distribution/retention and excretion of tungsten oxide after a single nose only inhalation exposure was evaluated based on urinary and fecal excretion over 165 days and an in vivo gamma globulin measurements of residual organ radioactivity at sacrifice.

GLP compliance:

no

Radiolabelling:

yes

Remarks:

[181]W

Species:

dog

Strain:

Beagle

Sex:

not specified

Details on test animals or test system and environmental conditions:

no data

Route of administration:

inhalation: aerosol

Vehicle:

not specified

Details on exposure:

- nose only inhalation
- All dogs were anesthetized with 27 mg pentobarbital per kilogram dog weight before exposure

Remarks:

Doses / Concentrations:
1.9 - 8 µCi of [181]WO3

No. of animals per sex per dose / concentration:

Six purebred beagle dogs (sex not specified)

Control animals:

not specified

Positive control reference chemical:

no

Details on study design:

- Several samples of expired air were collected at intervals during exposure; the activity in expired air was calculated from gamma-ray measurements of the electrostatic precipitator.
- The glass fiber filters, used to collect samples of the inhaled aerosol, were also measured by this technique.
- All samples were compared to known amounts of activity deposited on precipitator plates or glass fiber filters.
- The activity deposited in the respiratory tract of each experimental animal was estimated by three independent techniques: the first method involved subtraction of activity in expired air from that in inspired air; the second method estimated the deposited activity by means of in vivo gamma-ray measurements; and the third method was based on measurement of the activity excreted in the urine and and feces.

Details on dosing and sampling:

- Blood was sampled from the external jugular vein several times on the day of inhalation and at least daily for several days until the activity in the blood was less than the limit of detection.
- The blood, excreta and dogs were counted for gamma ray emission.
- Tissue samples were taken from all dogs at sacrifice, all samples were frozen.
- Tissue samples were counted between the two thin crystals in the dog counting configuration; the counting time for tissue samples was selected so that the coefficient of variation was less than 0.05 or 400 minutes, whichever was shorter.
- A few low level samples were counted 400 minutes without reaching the 0.05 level.
- The results were corrected for background, sample self-absorption and counting geometry and the activity in uCi was determined by comparison to an injection solution standard of known activity.

Statistics:

no data

Details on distribution in tissues:

- The values used for the deposition in the lung were based on the data from the excreta measurement.
- Deposition (fraction of the inhaled activity deposited in the nasopharyngeal, tracheobronchial and pulmonary compartments of the respiratory tract) in the respiratory tract ranged from 1.9 to 9.0 uCi; about 60% of the inhaled activity was deposited in the respiratory tract.
- The early lung position gamma-ray measurements detected about half of the deposited activity.
- In beagles breathing at a rate of about 30 inhalations per minute and a minute volume of 3.3 L, total deposition was about 60% of the inhaled activity, half of which was deposited in the lower portion of the respiratory tract lung clearance.
- Following inhalation, measurements indicated that the early increases in apparent activity in the lung area were due to removal of activity from the lungs and upper respiratory tract to the stomach.
- Initial measurements over the lung area represented less than the total deposited activity (average 42%), primarily due to activity deposited in the upper respiratory tract.
- A series of point source measurements located in the lungs, back of the throat near the epiglottis and the stomach, provided the following ratios of gamma-ray measurement efficiencies: lung/stomach, 1.17; throat/lung, 0.064; throat/stomach, 0.075.
- As the lung activity peaked, the visceral activity continued to rise until the lung position measurement returned to the value expected had the activity been removed from the body, rather than being swallowed.
- The available data tend to support the concept that the transport of activity via the ciliary escalator system to the esophagus, with a holdup in the throat due to the effect of anesthesia, is responsible for the observed early clearance pattern.

Details on excretion:

- An ingestion experiment carried out with a single beagle suggested that when a weakly acidic aqueous suspension of tungstic oxide (4% HCl) was given intragastrically, about 25% of the activity was excreted in the urine.
- 33% of the deposited activity appeared to enter the systemic circulation, most of it within 10 days after inhalation; this is relatively large and indicates that tungstic oxide is partially soluble in the lung fluid or that it is being removed to the systemic circulation by some mechanism such as phagocytosis, pinocytosis or direct penetration of the lung wall.
- The average half times was 69%, with a biological half-time of about 4 hours, 23% of the activity was removed with a biological half-time of about 20 hours, 4.6% of the activity was removed with a biological half-time of about 6.3 days and 3.0% of the activity was removed with a biological half-time of about 100 days.

Removal of inhaled tungstic oxide - visceral position:
- The pattern of clearance from the visceral position is similar to that seen in the lung position, with the exception of the measurements made during the first day (the visceral position measures most of the intestinal activity, as well as activity in the kidneys and bladder).

Removal of inhaled tungstic oxide - excretion measurements:
- The activity remaining in the body was calculated by subtracting the activity in the excreta from the initial body-burden.
- Approximately 90% of the activity was removed with a biological half-time of 14 hours; this is slightly longer than that measured in the visceral position whole-dog counts, probably due to the lack of fecal excretion in any of the dogs before 20 hours post-inhalation.
- Six percent of the activity was removed with a biological half-time of 5.8 days, which is just slightly less than that seen in the lung and visceral position whole-dog measurements.
- Four percent of the activity was removed with a biological half-time of 63 days, which is considerably shorter than that calculated from in vivo gamma-ray measurements.

Urine to Feces Ratios:
- Calculated using two different approaches; the total urine to feces ratio was calculated from the cumulative urinary and fecal activity at the termination if the excreta collection.
- These ratios showed much variation among the dogs; it was determined that the observed differences were due to different patterns of deposition or clearance.
- Comparison of these values with the values for the fraction of pulmonary activity entering the systemic circulation, indicating a relatively good relationship.
- The ratio of urinary to fecal excretion divided by the fraction going from lung to blood is between 3.0 and 3.8 for all dogs except one, and the average value was 3.28 with a standard deviation of 0.35; this appeared to indicate that the differences seen in the urine to feces ratios were due to variations in the lung clearance patterns of the various dogs.
- This one dog was excluded from the above calculations since one very early fecal sample was lost, and may have been responsible for the variation from other dogs.
- The second approach to the urine to feces ratio was calculation of the average daily urine to feces ratio.

Removal of tungstic oxide from the blood:
- Maximum blood activity averaged 64% of the systemic activity.
- Following inhalation of tungstic oxide, the rate of decrease in blood activity was clearly slower than that seen for injected sodium tungstate.
- By day 10 after inhalation, blood levels were just about equal to those seen one day after.

Metabolites identified:

not specified

Note: Some results are not reported here as they were unreadable in the availabe copy of the published report.

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
Following an inhalation exposure of tungsten trioxide 60% of the inhaled activity was deposited in the respiratory tract. Removal of the inhaled activity from the body was quite rapid with approximately 90% of the activity removed with a biological half-time of 14 hours.

Executive summary:

Tissue distribution/retention and excretion of tungsten oxide after a single nose only inhalation exposure was evaluated in 6 beagle dogs based on urinary and fecal excretion over 165 days and an in vivo gamma globulin measurements of residual organ radioactivity at sacrifice. 60% of the inhaled activity was deposited in the respiratory tract. Removal of the inhaled activity from the body was quite rapid with approximately 90% of the activity removed with a biological half-time of 14 hours.

Reference 3

Endpoint:

basic toxicokinetics

Type of information:

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

Adequacy of study:

key study

Study period:

2010-08-31 to 2010-01-29

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

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 physical-chemical properties, similar or lower transformation/dissolution results and similar or lower in vitro bioaccessibility in synthetic body fluids for tungsten dioxide (the target substance) than the source substances, 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: Tungsten Oxide
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:

reference to same study

Reason / purpose for cross-reference:

read-across: supporting information

Objective of study:

toxicokinetics

Qualifier:

according to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Principles of method if other than guideline:

The experimental design included toxicokinetic (TK) animals for analysis of tungstn oxide (also known as tungsten blue oxide or TBO) content during the 28 days of exposure (TK Sets 1-4) and to assess the elimination phase of the test substance after one day of exposure (TK Set 5).

GLP compliance:

yes

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, (St. Constant, Canada)
- Age at study initiation: approximately 8 weeks
- Weight at study initiation: One day following receipt, body weight ranges of the first shipment of rats 226 to 279 g (males). One day following receipt, body weight range of the second shipment of male rats was 207 to 234 g.
- Fasting period before study: no food or water was provided during exposures.
- Housing: At the start of food consumption measurements, the rats were individually housed in clear polycarbonate rodent cages (Allentown Caging Equipment Co., Allentown, NJ) equipped with an automatic watering system.
-Diet: Certified Rodent Chow 5002 meal (PMI Nutrition International, Inc., Brentwood, MO) was provided ad libitum, except during inhalation exposures and scheduled fasting periods. Diet analysis reports received from the supplier are maintained with facility records. The diet contained no known contaminants at levels that would be expected to interfere with the test substance or the animals or confound interpretation of the study.
- Water (e.g. ad libitum): Each rodent cage was provided with an automatic watering system (Edstrom Industries, Inc., Waterford, WI) supplying fresh city of Chicago water without additional treatment ad libitum, except during inhalation exposures.
- Acclimation period: The animals were quarantined for 2 weeks; To condition the animals for placement and restraint in the nose-only exposure tubes, and reduce stress during the exposure phase, the animals were acclimated to the restraining tubes during a three-day acclimation period. Animals were restrained for 1/4 (1.5 hours), 1/2 (3 hours), and 3/4 (4.5 hours) of the daily exposure duration (6 hours) on three non-holiday weekdays before the animals were exposed.


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18.6 to 23.0 degree C
- Humidity (%): 25.1-64.6%
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): automatic 12-hour light/dark cycle was maintained in the exposure and housing chamber laboratories.



IN-LIFE DATES: From: 2010-09-09 To: 2010-10-21

Route of administration:

inhalation: dust

Vehicle:

unchanged (no vehicle)

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: The nose-only chamber employed for test substance exposure was contained in an acrylic enclosure to isolate the exposure chamber and protect laboratory personnel. The dilution air to the atmosphere generator was of breathable quality and was filtered with a compressed air filter and a carbon absorber. The exhaust from the exposure chamber was moved through a particulate filter by a ring compressor and exhausted outside the building. Inlet and exhaust flows to and from the chamber were continuously monitored by rotameters.
- Method of holding animals in test chamber: During the inhalation exposures, the rats were restrained in nose-only exposure animal holding tubes (CH Technologies, Westwood, NJ). Animal tube loading and unloading, and tube insertion and removal from the exposure chamber were performed according to standard procedures designed to minimize stress to study rats. At all times that rats were restrained in holders, they were observed
frequently and when necessary, action was taken to avoid injury, death, or improper exposure. Prior to the start of the exposure, rats were transferred from their housing cages to the nose-only holding tubes. Following confirmation of correct animal number, the animals in the holders were inserted into the ports of the exposure chambers. Following the exposure, the holders were removed. The rats were removed from the holders and returned to their home cages. Chamber port rotation occurred weekly.
- System of generating particulates/aerosols: Test atmospheres in the exposure chambers were generated by aerosolizing the test substance using a compressed air-operated Wright Dust Aeorsol Generation System positioned over the chamber. Each inhalation exposure system was equipped with a separate aerosol generation system. The test substance was weighed out and packed into a dust reservoir daily. A constant speed rotating scraper separated a thin film of the test substance at the surface of the cake and delivered it into a dispersing unit, drawn in by aspiration and dispersed by a high velocity air jet. The resulting test atmosphere entered a mixing plenum where it was diluted with breathable quality compressed air to the target concentration prior to introduction to the nose-only inhalation exposure chamber.
- Air flow rate: The total airflow was set to produce an airflow range of approximately 0.5 to 1.0 L/min/exposure port.
- Method of particle size determination: The aerosol particle size distribution was monitored twice per week during the exposure phase of the study by an Aerodynamic Particle Sizer (APS) 3321 with Aerosol Diluter 3302A (both manufactured by TSI Inc., Shoreview, MN). The APS sizes particles in the range from 0.5 to 20 um using a time-of-flight technique that measures aerodynamic diameter in real time.


TEST ATMOSPHERE
- Brief description of analytical method used: The test atmosphere mass concentration was monitored gravimetrically by collecting gravimetric samples on pre-weighed glass fiber filters placed in closed-face filter holders. Samples were collected at a constant flow rate equal to the port flow of the delivery tube, and the total volume of air sampled was measured by a dry gas meter. Test atmosphere samples were collected at least three times during the exposure (generally, once during the first two hours, once during the middle two hours and once during the last two hours). The filter-collected samples were weighed and one filter per group per day (including the control to confirm the absence of test substance in the test atmosphere) was analyzed chemically to confirm the mass of TBO collected; percent recovery (chemical analysis concentration vs. gravimetric concentration) was calculated for each filter analyzed. Chemical analysis was conducted by means of ICP-mass spectrometry. In addition, the test atmosphere aerosol concentration in each chamber was monitored with a real-time aerosol sensor (model # pDR-1000AN, MIE, Inc. Bedford, MA). The sensors were employed only as a real-time indicator of short-term changes in aerosol concentration and were used in guiding laboratory personnel if concentration excursions were encountered.
- Samples taken from breathing zone: yes

Duration and frequency of treatment / exposure:

Set 1: 6 hours/day, 7 days/week for 28 days
Set 2: 6 hours/day for 3 days
Set 3: 6 hours/day for 7 days
Set 4: 6 hours/day for 14 days
Set 5: 6 hours with 7 day recovery

Remarks:

Doses / Concentrations:
0.08 and 0.65 mg/L (Target TBO concentration); 15.2 and 123.6 mg/kg/day (Target Inhaled Dose)

No. of animals per sex per dose / concentration:

Animals designated for toxicokinetic analysis were divided into five sets consisting of 4 males/set (time point) in each of the Low and High dose groups.

Control animals:

no

Positive control reference chemical:

no

Details on dosing and sampling:

PHARMACOKINETIC STUDY
- Tissues and body fluids sampled: at necropsy the brain, lungs, bone (femur), liver, kidney, spleen and reproductive organs were collected for analysis of TBO concentration. All toxicokinetic-designated animals were euthanized using sodium pentobarbital and exsanguinated from the abdominal aorta. Toxicokinetic animals were bled and necropsied as follows:

Set 1: Blood collection for the Low and High dose groups was performed on TK Day 0 [study Day 1 (pre-exposure)], and after the daily exposure on TK Days 1, 2, 3, 7, 14 and 28 (study Days 2, 3, 4, 8, 15 and 29); feces and urine were also collected from these animals overnight starting on TK Days 0, 1, 2, 3, 7, 14 and 28 (collection occurred the next day). These animals were necropsied on study Day 29. Blood was also collected on study Day 29, but was not chemically analyzed.

Set 2: Blood collection for the Low and High dose groups was performed on TK Day 3 (study Day 4) after the daily exposure and preserved for future evaluation. These animals were necropsied on TK Day 3.

Set 3: Blood collection for the Low and High dose groups was performed on TK Day 7 (study Day 8) after the daily exposure and preserved for future evaluation. These animals were necropsied on TK Day 7.

Set 4: Blood collection for the Low and High dose groups was performed on TK Day 14 (study Day 15) after the daily exposure and preserved for future evaluation. These animals were necropsied on TK Day 14.

Set 5: Blood collection for the Low and High dose groups was performed on this group on TK Day 0 [study Day 28 (pre-exposure)], after the exposure on TK Day 1 (study Day 29), and recovery Days 2, 3, 4, 5, 6 and 7) (study Days 30, 31, 32, 33, 34 and 35); feces and urine were also collected from these animals overnight starting on TK Days 0, 1, 2, 3, 4, 5, 6 and 7 (collection occurred the next day). These animals were necropsied on TK Day 8 (study Day 36) after the final urine and feces collection. Blood was also collected on TK Day 8, but was not chemically analyzed.

Statistics:

no data

Details on absorption:

In the single dose experiment, tungsten was absorbed systemically and blood tungsten concentration reached maximum (Tmax) at 0 hours post-exposure.

Details on distribution in tissues:

Repeat dose experiment:

From the repeat dose experiments, tungsten concentration in lung tissue was at least one order of magnitude greater than in any other organ collected, the lung being the primary organ for TBO (aka tungsten blue oxide or tungsten oxide) exposure via inhalation. In general, the femur and kidney ranked second and third highest in tungsten concentration on a per organ weight basis, respectively. The results indicated that the lung, femur and liver ranked first, second and third for total tungsten burden, respectively. The study day appeared to have little or no effect on the rank of tungsten distribution in tissue and organs. Tungsten concentration in tissue and organs increased with increasing dose, but not in a dose-proportionate manner.
Tungsten concentration in each organ increased with increasing inhalation exposure time for the lung, liver, kidney, spleen, testes, brain and femur, respectively. The increment was not significantly different between study Days 7 and 14, suggesting that steady-state absorption of inhaled TBO was reached on study Day 14. Compared with the steady-state concentration on study Day 14, tungsten in liver, kidney, testes and brain decreased at least 50% on study Day 29; however, unlike toxicokinetic Set 2 to 4 animals (necropsied immediately following termination of inhalation exposure on study Day 3, 7 or 14, respectively), the Set 1 animals were necropsied 24 hours after termination of exposure on study Day 29 to allow for overnight urine and feces collection. The results suggest that the functional elimination half-life of tungsten in those organs was less than 24 hours. On the contrary, tungsten in femur on study Day 29 was no different as compared to study Day 14, indicating that elimination of tungsten from femur was relatively slow as compared to other organs. The results were consistent with the Set 5 results (animals necropsied on Recovery Day 8 following a single inhalation exposure). Tungsten in femur on Recovery Day 8 (Set 5) was approximately one third as compared to that on study Day 3 (Set 2 animals) following multiple inhalation exposure, while tungsten concentration in the rest of organs was at least one order of magnitude lower.

Single administration experiment:

Following inhalation exposure of TBO, tungsten was absorbed systemically, as indicated by maximum blood concentration at 0 hour post-exposure. At 48 hours post-exposure, there was a slow elimination phase following an initial fast elimination phase for the 0.65 mg/L dose group (High). However, the second slow elimination phase was not evident for the 0.08 mg/L dose group (Low), which may be due to background noise of tungsten concentration. Based on the concentrations in the blood, the terminal phase half-life values were determined to be 23 ± 4.3 and 154 ± 92.8 hours for the 0.08 and 0.65 mg/L dose groups, respectively. Maximum blood tungsten concentration was 0.819 ± 0.215 and 10.9 ± 4.7 1.1g/g and area under the blood concentration-time curve extrapolated to infinity was 11.8 ± 3.29 and 148 ± 33.7 hr*ug/g for the 0.08 and 0.65 mg/L dose groups, respectively. These two exposure parameters increased proportionally with increasing TBO dose level. The systemic clearance based on the concentrations in the blood was 1.24 ± 0.39 and 0.78 ± 0.18 L/hr/kg for the 0.08 and 0.65 mg/L dose groups, respectively.

Details on excretion:

Repeat dose experiment:

The results from the repeat dose experiments indicate that the amount of tungsten excreted from feces was approximately three orders of magnitude greater than from urine. Since the nasal cavities are the major deposition site for inhaled particles in the rate, the study results suggest that most of the inhaled TBO(aka tungsten blue oxide or tungsten oxide) was deposited in the nasal passages and subsequently ingested into the gastrointestinal tract and excreted with the feces. The study results also indicate that the excretion rate of tungsten from feces and urine and tungsten concentration in blood increased with increasing TBO dose level; however, the effect of study day was sporadic and a discernible trend was not observed.

Single administration experiment:

From the single dose experiment, the results indicate that excretion of tungsten from the gastrointestinal tract was negligible after post-exposure Day 2 and 3 for Groups 2 (Low) and 4 (High), respectively. The results are consistent with the general consensus that insoluble particles deposited in the nasal and tracheobronchial airways would be cleared within 24 hours through mucus escalator followed by ingestion into gastrointestinal tract and excretion with the feces. In contrast, there was still detectable tungsten in urine on post-exposure Day 7.

Toxicokinetic parameters:

AUC: 11.8 ± 3.29 hr µg/g for the 0.08 mg/L dose group

Toxicokinetic parameters:

Cmax: 0.819 ± 0.215 µg/g for the 0.08 mg/L dose group

Toxicokinetic parameters:

half-life 1st: 23 ± 4.3 hours for the 0.08 mg/L dose group

Toxicokinetic parameters:

AUC: 148 ± 33.7 hr µg/g for the 0.65 mg/L dose group

Toxicokinetic parameters:

Cmax: 10.9 ± 4.7 µg/g for the 0.65 mg/L dose group

Toxicokinetic parameters:

half-life 1st: 154 ± 92.8 hours for the 0.65 mg/L dose group

Metabolites identified:

not measured

The mean MMADs of the test atmosphere were 2.63 and 2.74 um with GSDs of 1.89 and 1.92 for the low and high dose groups, respectively.

Overall means for TBO (aka tungsten blue oxide or tungsten oxide) concentrations were determined gravimetrically to be 0.081and 0.652 mg/L for the low and high dose groups, respectively. The TBO % recovery ranged from 100.83-102.38%. Small amounts of TBO in the chemically-analyzed filters for the Filtered Air Control group were attributed to contamination during the filter analysis processing and/or the calibration curve. The Filtered Air Control group filter-collected mean gravimetric value was 0.000 mg/L. The particle size distribution of the test atmosphere was within the respirable range. The overall mean TBO inhaled dose levels were 14.8 and 118.8 mg/kg/day for the lowand high dose groups, respectively. The overall mean male TBO inhaled dose levels were 13.7 and 110.2 mg/kg/day for the low and high dose groups, respectively. The overall mean female TBO inhaled dose levels were 15.8 and 127.3 mg/kg/day for the low and high dose groups, respectively. The male inhaled dose levels were 10-11% below the target levels for all groups, while the female inhaled dose levels were 3-5% above the target levels for all groups. Prior to exposure initiation, the homogeneity of the test atmosphere in each TBO exposure chamber was confirmed.

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results
Tungsten distribution in tissue and organs reached steady-state on study Day 14. With the exception of the femur, the functional elimination half-life of tungsten in most organs was less than 24 hours.

Executive summary:

Following inhalation exposure to TBO (aka tungsten blue oxide or tungsten oxide), tungsten was absorbed systemically with blood tungsten concentrations reaching maximum immediatly after exposure. The exposure parameters of Cmax and AUC increased proportionally with increasing TBO dose level: Cmax was 0.819 ± 0.215 and 10.9 ± 4.7 fig/g and AUC was 11.8 ± 3.29 and 148 ± 33.7 hr*Rg/g for the 0.08 and 0.65 mg/L dose groups, respectively. The systemic elimination half-life was 23 ± 4.3 and 154 ± 92.8 hours for the 0.08 and 0.65 mg/L dose groups, respectively, and the clearance rate was 1.24 ± 0.39 and 0.78 ± 0.18 L/hr/kg for the 0.08 and 0.65 mg/L dose groups, respectively. The majority of the inhaled TBO was excreted through the gastrointestinal tract. Tungsten concentration in lung tissue was at least one order of magnitude greater than in any other organ collected. In general, the femur and kidney ranked second and third highest, respectively, in tungsten concentration on a per organ weight basis. In terms of total tungsten burden in the organs, the lung, femur and liver ranked first, second and third, respectively. Tungsten distribution in tissue and organs reached steady-state on study Day 14. With the exception of the femur, the functional elimination half-life of tungsten in most organs was less than 24 hours.

Reference 4

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

January to March 2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Meets generally accepted scientific standards, well documented and acceptable for assessment.

Objective of study:

other: Leaching of Tungsten dioxide in syntethic biological fluids (termed bioaccessibility).

Qualifier:

no guideline available

Principles of method if other than guideline:

This report measured bioaccessibility of Tungsten dioxide in body fluid simulants as a surrogate for bioavailability.

GLP compliance:

no

Radiolabelling:

no

Species:

other: not applicable

Strain:

other: not applicable

Details on test animals or test system and environmental conditions:

Not applicable

Route of administration:

other: In vitro study

Vehicle:

other: not applicable

Details on exposure:

Not applicable

Duration and frequency of treatment / exposure:

Not applicable

Remarks:

Doses / Concentrations:
0.1 g of test substance in 50 mL of simulated fluid

No. of animals per sex per dose / concentration:

Not applicable

Control animals:

other: not applicable

Positive control reference chemical:

Not applicable

Details on study design:

Tungsten dioxide was extracted in leaching fluids for different time periods: 5hrs in simulated gastric fluid, 2 and 24 hrs in simulated interstitial and lysosomal solution and 12 hrs in artificial perspiration. The extractions were performed using 0.1 gram of sample in 50 ml of simulated fluid. A shaker water bath at a temperature of 37°C was used. All extractions were performed in triplicate. The extracts were analyzed for soluble tungsten using EPA Method #200.7 (ICP). Results were reported as ug W/g sample, % W/g sample and as % of total available W released.

Details on dosing and sampling:

Not applicable

Statistics:

Not applicable

Preliminary studies:

Not applicable

Details on absorption:

Not applicable

Details on distribution in tissues:

Not applicable

Details on excretion:

Not applicable

Metabolites identified:

not measured

Details on metabolites:

Not applicable

Table 1: Soluble Tungsten in gastric fluid

Extraction time in h	Weight used (g)	µg Tungsten/g Sample	% Tungsten release/Tungsten content
5	0.1003	1,994	0.23
(dup)	0.1034	1,886	0.22
(trip)	0.1048	2,052	0.24

 

Table 2: Soluble Tungsten in simulated interstitial fluid

Extraction time in h	Weight used (g)	µg Tungsten/g Sample	% Tungsten release/Tungsten content
2	0.1010	3,218	0.38
(dup)	0.1006	3,181	0.37
(trip)	0.1015	2,956	0.35
24	0.1039	7,267	0.85
(dup)	0.1046	6,597	0.77
(trip)	0.1036	6,226	0.73

 

Table 3: Soluble Tungsten in lysosomal fluid

Extraction time in h	Weight used (g)	µg Tungsten/g Sample	% Tungsten release/Tungsten content
2	0.1013	4,393	0.52
(dup)	0.1003	4,487	0.53
(trip)	0.1019	4,612	0.54
24	0.1024	29,150	3.42
(dup)	0.1008	26,835	3.15
(trip)	0.1026	28,606	3.36

 

Table 4: Soluble Tungsten in artificial perspiration

Extraction time in h	Weight used (g)	µg Tungsten/g Sample	% Tungsten release/Tungsten content
12	0.1028	38,473	4.52
(dup)	0.1017	39,381	4.62
(trip)	0.1036	37,645	4.42

 

 

 

Conclusions:

Interpretation of results (migrated information): bioaccumulation potential cannot be judged based on study results Data for read-across assessments for tungsten dioxide
Based on the results, the bioavailability of Tungsten dioxide would be expected to be low for all routes of administration and best at slightly acidic to neutral pH.

Executive summary:

This report measured bioaccessibility of Tungsten dioxide as a surrogate for bioavailability. To do this the soluble Tungsten was measured using the EPA method #200.7 (ICP) after incubation of Tungsten dioxide in simulated body fluids (simulated gastric fluid, simulated interstitial fluid, simulated lysosomal fluid, and artifical perspiration). Results were reported as ug W/g sample, % W/g sample and as % of total available W released.

Overview of W released in the different simulated body fluids:

Medium	T in h	% W-release from WO2
Simulated gastric fluid	5	0,23 %
Simulated interstitial fluid	2	0,37 %
	24	0,78 %
Simulated lysosomal fluid	2	0,53 %
	24	3,31 %
Artifical perspiration	12	4,52%

 

In summary, release of Tungsten from WO₂ was best in simulated lysosomal fluid and artificial perspiration. The bioavailability in the fluids ranged from 0,23 % (simulated gastric fluid) to 4,52 % (artificial perspiration). Thus, the maximum solubility was measured in artificial perspiration. Based on the results, the bioavailability of Tungsten dioxide would be expected to be low for all routes of administration and best at slightly acidic to neutral pH.

Description of key information

In vitro bioavailability studies in artificial body fluids were conducted with tungsten dioxide and other tungsten oxides providing the base for read-across of toxicological endpoints. In addition basic toxicokinetic was assessed according to OECD 417 on tungsten oxide (also known as tungsten blue oxide or TBO) and in a non-guideline inhalation study in beagles .

The solubility of tungsten dioxide was determined in artificial body fluids (gastric fluid, interstitial fluid, lysosomal fluid, and artificial perspiration; KMHC 2012). Results were reported as µg W/g sample, % W/g sample and as % of total available W released. The bioavailability ranged from 0.23 % (5h, gastric fluid) to 4.52 % (12h, artificial perspiration). Based on the results, the bioavailability of tungsten dioxide would be expected to be low for all routes of administration and best at slightly acidic to neutral pH.

Similar data are available for other tungsten oxides (IITRI, 2010) that were used to verify the applicability of each read across.The bioavailability of tungsten trioxide was determined in artificial gastric, alveolar, lysosomal, interstitial fluids, and sweat. The bioavailability ranged from 0.0055% (gastric fluid) to 39% (interstitial fluid). The maximum bioavailability of tungsten from tungsten trioxide was determined at 72 hours for the simulated alveolar, lysosomal and interstitial fluids (34, 38 and 39%, respectively). Based on the results, the bioavailability of tungsten from tungsten trioxide would be expected to be low for the oral route of administration, but moderate for the inhalation route. 

The bioaccessibility of tungsten from WO3 and WO2 is the basis for read-across. The release was consistently lower for WO2 compared to WO3. Only at very low pH WO3 was virtually not soluble (5h simulated gastric fluid; 0.0055%) compared to 0.23% for WO2. The value of 0.23% is rather low. As a potential oral toxicity would be elicited by the combined gastro-intestinal release, the higher solubility of WO3 in the gut (pH 5-8.3) is assumed to result in a significant higher total release of tungsten ions. Therefore the oral toxicity studies conducted with WO3 are considered to be protective when read-across to WO2.

In an in vivo study, tissue distribution, retention, and excretion were determined following administration of tungsten oxide after a single nose-only exposure to six beagle dogs. 60% of the inhaled activity was deposited in the respiratory tract. Removal of the inhaled activity from the body was quite rapid, with approximately 90% of the activity removed with a biological half-time of 14 hours.

In addition a toxicokinetic study conducted according to OECD 417 on TBO was used for read-across. When TBO was administered via inhalation, tungsten was absorbed systemically. Cmax and AUC increased proportionally with increasing TBO dose level: Cmax was 0.819 ± 0.215 and 10.9 ± 4.7 fig/g, and AUC was 11.8 ± 3.29 and 148 ± 33.7 hr*Rg/g for the 0.08 and 0.65 mg/L dose groups, respectively. The systemic elimination half-life was 23 ± 4.3 and 154 ± 92.8 hours for the 0.08 and 0.65 mg/L dose groups, respectively, and the clearance rate was 1.24 ± 0.39 and 0.78 ± 0.18 L/hr/kg for the 0.08 and 0.65 mg/L dose groups, respectively. The majority of the inhaled TBO was excreted through the gastrointestinal tract. Tungsten concentration in lung tissue was at least one order of magnitude greater than in any other organ collected. In general, the femur and kidney ranked second and third highest, respectively, in tungsten concentration on a per organ weight basis. In terms of total tungsten burden in the organs, the lung, femur and liver ranked first, second and third, respectively. Tungsten distribution in tissue and organs reached steady-state on study Day 14. With the exception of the femur, the functional elimination half-life of tungsten in most organs was less than 24 hours.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential