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Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Sodium tungstate was negative for mutagenicity in an in vitro bacterial reverse mutation assay conducted according to OECD 471, anin vitro chromosome aberration assay conducted according to OECD 473, an in vitro L5178Y TK +/- Mouse Lymphoma Forward Mutation Assay conducted according to OECD 476.

Link to relevant study records

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Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003-07-16 to 2003-12-22
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)
Deviations:
no
GLP compliance:
yes
Type of assay:
in vitro mammalian chromosome aberration test
Species / strain / cell type:
Chinese hamster Ovary (CHO)
Details on mammalian cell type (if applicable):
- Type and identity of media: The CHO cells were grown in McCoy's 5a culture medium, which was supplemented
with approx. 10% heat-inactivated fetal bovine serum (FBS), L-glutatnine (2mM), penicillin G (100 units/mL), and streptomycin (100 ug/mL).
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes
- Periodically checked for karyotype stability: yes
Additional strain / cell type characteristics:
other: permanent cell line with an average cycle time of 12 to 14 hours and a modal chromosome number of 21
Metabolic activation:
with and without
Metabolic activation system:
Aroclor 1254 induced rat liver S9
Test concentrations with justification for top dose:
Initial Assay (3 hour treatment with and without S9)-23.7, 33.9, 48.4, 69.2, 98.9, 141, 202, 288, 412, 588, 840, 1200, 1720, 2450, and 3500 ug/ml
Confirmatory assay (3 hour treatment with S9)-500, 1000, 1400, 2100, 2880, and 3500 ug/ml
Confirmatory assay (20 hour treatment without S9)-250, 500, 1000, 1400, 2100, 2800, and 3500 ug/ml

Vehicle / solvent:
- Vehicle(s)/solvent(s) used: Cell culture grade water
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
mitomycin C
Remarks:
Non-activated test system Migrated to IUCLID6: 0.750 and 1.50 ug/mL, for the 3-hour treatment, 0.200 and 0.400 ug/mL, for 20-hour treatment
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
cyclophosphamide
Remarks:
Activated test system Migrated to IUCLID6: 7.50 and 12.5 ug/mL, initial assay; 7.50 ug/mL, confirmatory assay
Details on test system and experimental conditions:
METHOD OF APPLICATION: in medium

DURATION
- Exposure duration: Initial assay (3 hours in the presence and absence of S9); Confirmatory assay (3 hours in the presence of S9 and 20 hours in the absence of S9)
- Fixation time (start of exposure up to fixation or harvest of cells): 20 hours with Colcemid present during the last 2 +/- 0.5 hours
SPINDLE INHIBITOR (cytogenetic assays): Colcemid
STAIN (for cytogenetic assays): Giemsa

NUMBER OF REPLICATIONS: 2

NUMBER OF CELLS EVALUATED: 100 hundred cells, when possible, from each replicate were anlyzed for the different types of chromosomal aberrations. At least 25 cells were analyzed from those cultures that had greater than 25 % of cells with one or more aberrations.

DETERMINATION OF CYTOTOXICITY
- Method: Prior to the harvest of the cultures, visual observations of cytotoxicity were made. These observations included an assessment of the percent confluence of the cell monolayers within the culture flasks. The cultures were also evaluated for the presence of mitotic (large rounded cells) or dead cells floating in the medium; mitotic index

OTHER EXAMINATIONS:
- Determination of polyploidy: yes
- Determination of endoreplication: yes



Evaluation criteria:
Evaluation of a Positive Response- The test substance was considered positive for inducing chromosomal aberrations if a significant increase (the difference was considered significant when pEvaluation of a Negative Response- The test substance was considered negative for inducing chromosomal aberrations if no significant increase was observed in the number of cells with chromosomal aberrations at any of the concentrations.
Equivocal Evaluation- Although most assays give clearly positive or negative results, in rare cases the data set would preclude making a definitive judgment about the activity of the test substance. Results might remain equivocal or questionable regardless of the number of times the assay is repeated.
Statistics:
Statistical analysis employed a Cochran-Amitage test for linear trend and Fisher's Exact Test to compare the percentage of cells with aberrations in treated cells to the results obtained for the vehicle controls.
Statistical analysis was also performed for cells exhibiting polyploidy and/or endoreduplication in order to indicate significant (p
Key result
Species / strain:
Chinese hamster Ovary (CHO)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
In the 20 hour treatment confirmatory assay.
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
TEST-SPECIFIC CONFOUNDING FACTORS
- Effects of pH: At a dose concentration of 20000 ug/mL, the pH was 8.5 (pH of the culture medium was 8.0) and at 3300 ug/mL, the pH was 8.0.
- Water solubility: In the cell culture grade water, the test substance formed transparent, colorless solutions at 33.0 and 200 mg/mL.
- Precipitation: At a dose concentration of 20000 ug/mL, no precipitate was observed and the culture medium became a slightly darker shade of red. At 3300 ug/mL, no precipitate was observed and no change in the appearance of the culture medium was observed.

ADDITIONAL INFORMATION ON CYTOTOXICITY:
1. Initial assay in the absence of S9 with a 3-hour treatment period: A slight reduction in the number of dividing cells was visible. Reductions of 0 and 8 % were observed in the mitotic indices of the cultures treated with 2450 and 3500 ug/ml, respectively, as compared with the vehicle control cultures.
2. Initial assay in the presence of S9 with a 3-hour treatment period: Reductions of 0 and 6 % were observed in the mitotic indices of the cultures treated with 2450 and 3500 ug/ml, respectively, as compared with the vehicle control cultures.
3. Confirmatory assay in the absence of S9 with a 20-hour treatment period: A slight reduction in dividing cells was visible at 500 and 1000 ug/ml and a reduction was visible at 1400-3500 ug/ml. Monolayer confluence as compared to the vehicle control for 1000, 1400, 2100, 2800, and 3500 ug/ml were 71, 57, 57, 57, and 57 %, respectively. Reductions of 29, 60, 77, 86, 82, 91, and 100 % were observed in the mitotic indices of the cultures treated with 250, 500, 1000, 1400, 2100, 2800, and 3500 ug/ml, respectively, as compared with the vehicle control cultures.
4. Confirmatory assay in the presence of S9 with a 3-hour treatment period- Reductions of 0 and 1 % were observed in the mitotic indices of the cultures treated with 2800 and 3500 ug/ml, respectively, as compared with the vehicle control cultures.

CHROMOSOME ABERRATIONS:
1. Initial assay in the absence of S9 with a 3-hour treatment period: Chromosomal aberrations were analyzed from the cultures treated with 1200, 1720, 2450, and 3500 ug/ml. No significant increase in cells with chromosomal aberrations, polyploidy, or endoreduplication was observed in the cultures analyzed.
2. Initial assay in the presence of S9 with a 3-hour treatment period: Chromosome aberrations were analyzed from the cultures treated with 1200, 1720, 2450, and 3500 ug/ml. No significant increase in cells with chromosome aberrations, polyploidy, or endoreduplication was observed in the cultures analyzed.
3. Confirmatory assay in the absence of S9 with a 20-hour treatment period-Chromosomal aberrations were analyzed from the cultures treated with 250, 500, and 1000 mg/ml. No significant increase in cells with chromosomal aberrations or polyploidy was observed in the cultures analyzed. A weakly significant increase in endoreduplication was observed in the cultures treated with 1000 ug/ml. There was no clear understanding of the mechanism or meaning of this induction. The weak increase was observed at a single toxic dose level and the significance was probably a statistical anomaly due to 0% endoreduplication in the vehicle controls. Thus, the significance of the observation of endoreduplication is debatable since the increase observed was probably related to toxicity and not to any potential of the test substance to inhibit mitotic processes.
4. Confirmatory assay in the presence of S9 with a 3-hour treatment period- Chromosomal aberrations were analyzed from the cultures treated with 1400, 2100, 2800, and 3500 ug/ml. No significant increase in the cells with chromosomal aberrations, polyploidy, or endoreduplication was observed in the cultures analyzed.
5. Positive control- Both positive controls induced chromosomal aberrations.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.
Conclusions:
The test substance was considered negative for inducing stuctural chromosomal aberrations in CHO cells with and without metabolic activation.
Executive summary:

The objective of this in vitro assay was to evaluate the ability of sodium tungstate to induce chromosomal aberrations in cultured Chinese hamster ovary (CHO) cells with and without an exogenous metabolic activation system.

The test article was dissolved in cell culture grade water for the assay. The highest concentration tested in the assay was 3500 ug/mL, which is slightly >10 mM of Sodium tungstate dihydrate (molecular weight=329.86; 10 mM=3299 ug/mL), the high dose recommended for this assay by the OECD Testing Guidelines. All dosing was achieved using dosing volumes of 10% (100 uL/mL) and the vehicle control cultures were treated with 100 uL/mL of cell culture grade water.

In the initial chromosomal aberrations assay, the treatment period was for approx. 3 hours without and with metabolic activation. Cultures were harvested approx. 20 hours from the initiation of treatment. Concentrations of 23.7, 33.9, 48.4, 69.2, 98.9, 141, 202, 288, 412, 588, 840, 1200, 1720, 2450, and 3500 ug/mL were tested with and without metabolic activation. Cultures treated with concentrations of 1200, 1720, 2450, and 3500 ug/mL without and with metabolic activation were analyzed for chromosomal aberrations. No significant increase in cells with chromosomal aberrations, polyploidy, or endoreduplication was observed in the cultures analyzed.

In a confirmatory chromosomal aberrations assay, the treatment period was for approx. 20 hours without metabolic activation and approx. 3 hours with metabolic activation and the cultures were harvested approx. 20 hours from the initiation of treatment. Concentrations of 250, 500, 1000, 1400, 2100, 2800, and 3500 ug/mL, were tested without metabolic activation and 500, 1000, 1400, 2100, 2800, and 3500 ug/mL were tested with metabolic activation. Cultures treated with concentrations of 250, 500, and 1000 ug/mL without metabolic activation and 1400, 2100, 2800, and 3500 ug/mL with metabolic activation were analyzed for chromosomal aberrations. No significant increase in cells with chromosomal aberrations or polyploidy, and no biologically relevant increase in endoreduplication was observed in the cultures analyzed.

The test article, sodium tungstate, was considered negative for inducing structural chromosomal aberrations in CHO cells with and without metabolic activation.


Endpoint:
in vitro gene mutation study in mammalian cells
Remarks:
Type of genotoxicity: gene mutation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003-07-17 to 2004-01-07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)
Deviations:
yes
Remarks:
The top concentration used in the assay (3500 ug/mL) is slightly above the recommended testing limit (10 mM) for the assay.
GLP compliance:
yes
Type of assay:
mammalian cell gene mutation assay
Target gene:
Thymidine kinase locus
Species / strain / cell type:
mouse lymphoma L5178Y cells
Details on mammalian cell type (if applicable):
- Type and identity of media: The medium used for the study was RPMI 1640 supplemented with horse serum (10 % by volume), pluronic F68, L-glutamine, sodium pyruvate, penicillin and streptomycin. Treatment medium was Fischer's medium with the same medium supplements used in the culture medium except that the horse serum concentration was reduced to 5 % by volume. Cloning medium consisted of the RPMI 1640 culture medium with up to 20 % horse serum, without Pluronic F68 and with the addition of 0.24 % Noble agar to achieve a semi-solid state. Selection medium was cloning medium that contained 3 ug/mL of 5-trifluorothymidine.
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes
- Periodically checked for karyotype stability: yes
- Periodically "cleansed" against high spontaneous background: yes
Additional strain / cell type characteristics:
other: heterozygous at the TK locus
Metabolic activation:
with and without
Metabolic activation system:
Aroclor 1254 induced rat liver S9
Test concentrations with justification for top dose:
62.5, 125, 250, 500, 1000, 1500, 2000, 2500, 3000 and 3500 ug/mL
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: Water
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
methylmethanesulfonate
Remarks:
Non-activation assay Migrated to IUCLID6: 13 ug/mL
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: Methylcholanthrene-2 and 4 ug/mL
Remarks:
Activation assay
Details on test system and experimental conditions:
METHOD OF APPLICATION: in medium


DURATION
- Exposure duration: 4 hours
- Expression time (cells in growth medium): 2 days
- Selection time (if incubation with a selection agent): 14 days


SELECTION AGENT (mutation assays): 5-trifluorothymidine


NUMBER OF REPLICATIONS: 3


NUMBER OF CELLS EVALUATED: 3 x 10^6 cells


DETERMINATION OF CYTOTOXICITY
- Method: relative total growth


OTHER: Sizing Analysis- Both the small and large colonies were quantified for all cultures. A bimodal curve was generated and small and large colonies were quantitated by the areas under the curves. The large colonies presumably arose from point mutations and the small colonies from chromosome changes.

Evaluation criteria:
See below
Statistics:
no data
Key result
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
TEST-SPECIFIC CONFOUNDING FACTORS:
- Precipitation: The test substance formed a transparent, colorless solution in water at 35 mg/mL, the highest concentration prepared for use in the assay. The test substance remained soluble at all concentrations tested.

RANGE-FINDING/SCREENING STUDIES: Cells were treated with the test substance for approximately 4 hours in the presence and absence of S9 activation at concentrations ranging from 6.90-3500 ug/mL. Test substance concentration for the main gene mutation assay were chosen to cover a toxicity range from 10 % to 20 % survival to no apparent effect on growth compared to the vehicle control. If little or no toxicity was observed and solubility was maintained, the mutation experiment was initiated with a maximum concentration of 5 mg/mL or 10 mM (whichever was lowest). If precipitation of the test substance occurred in the culture medium, the maximum applied dose was at least twice the solubility limit in culture medium. In this assay, the high dose was slightly higher than the OECD recommended guideline of 10 mM.
In the non-activation and activation assays, the test substance induced no cytotoxicity to weak cytotoxicity up to and including 1750 ug/mL and moderate cytotoxicity at 3500 ug/mL.


COMPARISON WITH HISTORICAL CONTROL DATA: One of the vehicle control cultures for the initial assay in the absence of metabolic activation (144.8 x 10^-6) was slightly above historical data range (36.4 to 135.7 x 10^-6) for mutant frequency. In this same assay one of the positive control cultures (522.0 x 10^-6) was also above the historical data range (227.0 to 487.4 x 10^-6) for mutant frequency. In addition, one vehicle control culture (139.1 x 10^-6) in the initial mutation assay with activation was slightly above the historical data range (34.0 to 123.9 x 10^-6) for mutant frequency.


ADDITIONAL INFORMATION ON CYTOTOXICITY:
1. Initial Non-activation Mutation Assay-Concentrations at 62.5 and 125 ug/mL were discarded because a sufficient number of higher concentrations were available. The remaining eight treatments induced no cytotoxicity to moderate cytotoxicity (88.3 % (250 ug/mL) to 34.0 % (3000 ug/mL) relative growths).
2. Confirmatory Non-activation Mutation Assay- Concentrations at 62.5 and 125 ug/mL were terminated because there were sufficient higher concentrations available for analysis. The remaining eight concentrations induced no cytotoxicity to high cytotoxicity (120.3 % (250 ug/mL) to 13 % (3500 ug/mL) relative growth).
3. Initial Activation Mutation Assay- Concentrations at 62.5 and 125 ug/mL were terminated because there were sufficient higher concentrations available for analysis. The remaining eight concentrations induced no cytotoxicity (117.2 % to 81.8 % relative growths).
4. Confirmatory Activation Mutation Assay- Concentrations at 62.5 and 125 ug/mL were terminated because there were sufficient higher concentrations available for analysis. The remaining eight concentrations induced no cytotoxicity to moderate cytotoxicity (95.5 % (250 ug/mL) to 39.9 % (3500 ug/mL) relative growths).


OTHER: The average cloning efficiencies for the vehicle control were 91.4 % and 110.9 % without metabolic activation and 96.6 % and 109.5 % with metabolic activation, which demonstrated acceptable cloning conditions for the assays. The positive control cultures induced large increases in mutant frequencies that were greatly in excess of the minimum criteria.
Mutant colonies from all the cultures showed the expected bimodal distribution, and mutant colonies from the positive control cultures showed both small and large colonies.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.
Conclusions:
The test substance was reported as negative for inducing forward mutations at the TK locus in L5178Y mouse lymphoma cells in the presence and absence of Aroclor 1254 induced rat liver S9.
Executive summary:

The objective of thisin vitroassay was to evaluate the ability of sodium tungstate to induce forward mutations at the thymidine kinase (TK) locus in the mouse lymphoma L5178Y cell line. The test article, Sodium Tungstate Dihydrate, formed a transparent, colorless solution in the vehicle (water) at 35 mg/mL. Thirty-five mg/mL was the highest concentration prepared for use in the assay and is slightly greater than the OECD Testing Guidelines of 10 mM (molecular weight=329.86; 10 mM=3299 ug/mL). The test article remained soluble at all concentrations tested.

The test article, sodium tungstate dihydrate, was tested in a preliminary dose range finding assay with a treatment period of approximately 4 hours both with and without S9 metabolic activation. Ten dose levels were used in each case that ranged from 6.90 to 3500 ug/mL; a vehicle control was included under each activation condition.

In both the nonactivation and activation dose range finding assays, sodium tungstate dihydrate induced no cytotoxicity to weak cytotoxicity up to and including 1750 ug/mL, and moderate cytotoxicity at 3500 ug/mL. The test article concentrations chosen for the mutation assays were based on these results.

In the initial nonactivation mutation assay, eight doses ranging from 250 to 3500 ug/ml were analyzed for mutant induction and no cytotoxicity to moderate cytotoxicity was induced. None of the concentrations induced a mutant frequency that exceeded the minimum criteria for a positive response. A confirmatory assay was performed. In the confirmatory nonactivation mutation assay, eight doses ranging from 250 to 3500 ug/mL were also analyzed and no cytotoxicity to high cytotoxicity was induced. None of the concentrations induced a mutant frequency that exceeded the minimum criteria for a positive response. Therefore, the test article was evaluated as negative without metabolic activation.

In the initial activation mutation assay, eight doses ranging from 250 to 3500 ug/mL were analyzed and no cytotoxicity was induced. None of the concentrations induced a mutant frequency that exceeded the minimum criteria for a positive response. A confirmatory assay was performed.

In the confirmatory activation mutation assay, eight doses ranging from 250 to 3500 ug/mL were also analyzed and no cytotoxicity to moderate cytotoxicity was induced. None of the concentrations induced a mutant frequency that exceeded the minimum criteria for a positive response. Therefore, the test article was evaluated as negative without metabolic activation.

The test article, sodium tungstate, was evaluated as negative for inducing forward mutations at the TK locus in L5178Y mouse lymphoma cells, under activation and nonactivation conditions used for this assay.

Endpoint:
in vitro gene mutation study in bacteria
Remarks:
Type of genotoxicity: gene mutation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003-07-16 to 2004-01-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to other study
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
no
GLP compliance:
yes
Type of assay:
bacterial forward mutation assay
Target gene:
Histidine locus and tryptophan locus
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Species / strain / cell type:
E. coli WP2 uvr A
Metabolic activation:
with and without
Metabolic activation system:
Aroclor 1254 induced rat liver S9
Test concentrations with justification for top dose:
33.3, 100, 333, 1000, 3330, and 5000 ug/plate
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: deionized water
- Justification for choice of solvent/vehicle: In solubility testing, the test substance was observed to form a transparent, colorless solution in deionized water at concentrations of 200 and 33.0 mg/ml.
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
benzo(a)pyrene
Remarks:
Activated test system Migrated to IUCLID6: Used for strain TA98 at 2.5 ug/plate
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
2-nitrofluorene
Remarks:
Non-activated test system Migrated to IUCLID6: Used for strain TA98 at 1.0 ug/plate
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 2-aminoanthracene-used for strains TA100, TA1535, TA1537 and WP2uvrA at 2.5, 2.5, 2.5, and 25.0 ug/plate, respectively.
Remarks:
Activated test system
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
sodium azide
Remarks:
Non-activated test system Migrated to IUCLID6: Used for strains TA100 and TA1535 at 2.0 ug/plate.
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: ICR-191-used for strain TA1537 at 2.0 ug/plate.
Remarks:
Non-activated test system
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
4-nitroquinoline-N-oxide
Remarks:
Non-activated test system Migrated to IUCLID6: Used for strain WP2uvrA at 1.0 ug/plate.
Details on test system and experimental conditions:
METHOD OF APPLICATION: in agar (plate incorporation)


DURATION
- Exposure duration: 52 +/- 4 hours
- Selection time (if incubation with a selection agent):

SELECTION AGENT (mutation assays): histidine (Salmonella strains) and trypophan (E. coli strain)

NUMBER OF REPLICATIONS: 3

DETERMINATION OF CYTOTOXICITY
- Method: Evaluation of the bacterial background lawn


Evaluation criteria:
Tester Strains TA98, TA100, and WP2uvrA- For the test substance to be considered positive, it had to produce at least a 2-fold increase in the mean revertants per plate of at least one of the tester strains over the mean revertants per plate of the appropriate vehicle control. This increase in the mean number of revertants per plate had to be accompanied by a dose response to increasing concentrations of the test substance.

Tester Strains TA1535 and TA1537-For the test substance to be considered positive, it had to produce at least a 3-fold increase in the mean revertants per plate of at least one of the tester strains over the mean revertant per plate of the appropriate vehicle control. This increase in the mean number of revertants per plate had to be accompanied by a dose response to increasing concentrations of the test substance.
Species / strain:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Species / strain:
E. coli WP2 uvr A
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
TEST-SPECIFIC CONFOUNDING FACTORS
- Water solubility: The test substance was observed to form a transparent, colorless, non-viscous solution in deionized water at 100 mg/ml, and remained in solution at all succeeding dilutions prepared.

RANGE-FINDING/SCREENING STUDIES: The test substance was tested for toxicity using tester strains TA100 and WP2uvrA in the presence and absence of metabolic activation at concentrations ranging from 6.67-5000 ug/plate. No indications of cytotoxicity were observed at any concentration in the presence or absence of metabolic activation, therefore, 5000 ug/plate was chosen as the high dose for the mutagenicity assays.

COMPARISON WITH HISTORICAL CONTROL DATA: All values were within historical control range.

OTHER: In the initial mutagenicity assay, tester strain TA98 did not exhibit the characteristic mean number of spontaneous revertants per plate in the absence of S9 as specified in the protocol, and for this reason the data was not used to evaluate the test substance. The test substance was retested in TA98 in the absence of S9. All other data generated in the initial mutagenicity assay were acceptable, and no positive increases were observed in the mean number of revertants per plate with any of the tester strains in the presence or absence of S9.
In the confirmatory mutagenicity assay, tester strain TA100 did not exhibit the characteristic number of mean spontaneous revertants per plate in the absence of S9 mix as specified in the protocol, and for this reason the data was not used to evaluate the test substance. The test substance was re-tested in TA100 in the absence of S9. All other data generated in the confirmatory assay were acceptable, and no positive increases were observed in the mean number of revertants per plate with any of the tester strains in either the presence or absence of S9.
In the repeat assays with TA100 and TA98, no positive increases in the mean number of revertants were observed.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.
Conclusions:
Under the conditions of the study, the test substance did not cause a positive increase in the mean number of revertants per plate with any of the tester strains either in the presence or absence of metabolic activation.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

Sodium tungstate was negative for mutagenicity in an in vivo micronucleus assay conducted according to OECD 474.

Link to relevant study records
Reference
Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003-07-16 to 2004-01-06
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study was conducted according to OECD guideline 474 and GLP.
Qualifier:
according to guideline
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Deviations:
no
GLP compliance:
yes
Type of assay:
micronucleus assay
Species:
mouse
Strain:
other: Crl:CD-1 (ICR)BR
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories, Portage MI
- Age at study initiation: 9 weeks at time of dosing
- Weight at study initiation: 30.3 to 37.9 grams at the time of dosing
- Assigned to test groups randomly: yes, by a computer program
- Housing: The animals were housed in sanitary polycarbonate cages containing Sani-Chips Hardwood Chip Laboratory bedding. The animals were housed, separated by gender, up to five animals per cage during acclimation, and by full dose group/harvest timepoint after randomization.
- Diet: PMI Feeds, Inc. Certified Rodent Diet #5002 ad libitum
- Water: tap water ad libitum
- Acclimation period: at least 5 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 64-79 degrees F
- Humidity (%): 30-70
- Air changes (per hr): at least 10 per hour
- Photoperiod (hrs dark / hrs light): 12 hours light/12 hours dark


IN-LIFE DATES: From: 2003-08-25 and 2003-08-26
Route of administration:
oral: gavage
Vehicle:
- Vehicle(s)/solvent(s) used: corn oil
- Concentration of test material in vehicle: 25, 50, and 100 mg/ml for initial test and 75 mg/ml for repeat test
- Amount of vehicle (if gavage or dermal): 10 ml/kg
- Lot/batch no. (if required): 12-406
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: Prior to dosing, each concentration of the test substance was prepared by adding the appropriate volume of the vehicle to a pre-weighed quantitiy of the test substance and mixing, forming homogeneous suspensions. The formulations were held at room temperature prior to dosing and stirred during the dosing procedure.

Duration of treatment / exposure:
Animals received a single oral gavage dose of the test substance.
Frequency of treatment:
Animals received a single oral gavage dose of the test substance.
Post exposure period:
24 hours (all dose groups) and 48 hours (vehicle control, positive control, 750 mg/kg and 1000 mg/kg groups only)
Remarks:
Doses / Concentrations:
250, 500, and 1000 mg/kg
Basis:
actual ingested
initial assay
Remarks:
Doses / Concentrations:
750 mg/kg
Basis:
actual ingested
repeat assay
No. of animals per sex per dose:
6 male animals/dose/time point (only 5 animals/dose/time point were used for the actual analysis)
Control animals:
yes, concurrent vehicle
Positive control(s):
Cyclophosphamide
- Route of administration: oral gavage
- Doses / concentrations: 80 mg/kg
Tissues and cell types examined:
erythrocytes (bone marrow)
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION: The high dose in the micronucleus assay was the maximum tolerated dose determined by the range-finding study. This dose should have produced some indication of toxicity, e.g., toxic signs, death, or depression of the ratio of PCEs to normochromatic erythrocytes (NCEs).

TREATMENT AND SAMPLING TIMES (in addition to information in specific fields): 24 and 48 hours (vehicle and high dose group only

DETAILS OF SLIDE PREPARATION: At the appropriate harvest timepoint, the animals were euthanized by CO2 inhalation followed by incision of the diaphragm. The hind limb bones (tibias) were removed from marrow extraction from five surviving animals in each treatment and control group. For each animal, the marrow flushed from the bones was combined in an individual centrifuge tube containing 3 to 5 ml fetal bovine serum.
Following centrifugation to pellet the tissue, the supernatant was removed by aspiration and portions of the pellet were spread on slides and air-dried. The slides were fixed in methanol, stained in May-Grunswald solution followed by Giemsa, and protected by permanently mounted coverslips.

METHOD OF ANALYSIS: The slides were scored for micronuclei and the PCE to NCE cell ratio. The micronucleus frequency (expressed as percent micronucleated cells) was determined by analyzing the number of micronucleated PCEs from at least 2000 PCEs per animal. The PCE:NCE ratio was determined by scoring the number of PCEs and NCEs observed while scoring at least the first 500 erythrocytes per animal.
Micronuclei were darkly stained and generally round, although almond and ring shaped micronuclei occasionally occurred. Micronuclei were sharp bordered and generally between one-twentieth and one-fifth the size of the PCEs. The unit of scoring was the micronucleated cell, not the micronucleus; thus, the occasional cells with more than one micronucleus was counted as one micronucleated PCE, not two (or more) micronuclei.
The staining procedure permitted the differentiation by color of PCEs and NCEs (bluish-gray and red, respectively).
The historical background frequency of micronucleated cells was expressed as the percentage of micronucleated cells based on the number of PCEs analyzed.


Evaluation criteria:
The criteria for a positive response were the detection of a statistically significant increase in micronucleated PCEs for at least one dose level, and a statistically significant dose-related response. If both of these were not present, than the result was negative. Statistical significance was not the only determinate of a positive response; the Study Director also considered the biological relevance of the results in the final evaluation.
Statistics:
Assay data analysis was performed using an analysis of variance on untransformed proportions of cells with micronuclei per animal and on untransformed PCE:NCE ratios when the variances were homogenous. Ranked proportions were used for heterogeneous variances. If the analysis of variance was statistically significant (p<=0.05), a Dunnett's t-test was used to determine which dose groups, if any, were statistically significantly different from the vehicle control. Analyses were performed separately for each sampling time.
Sex:
male
Genotoxicity:
negative
Toxicity:
yes
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
RESULTS OF RANGE-FINDING STUDY
- Dose range: 500-2000 mg/kg
- Clinical signs of toxicity in test animals: Clinical signs included slightly hypoactive, soft feces, rough haircoat, recumbent, cold to touch, opaque eyes, and hypoactive.
- Harvest times: Animals were analyzed at 1 hour, 4 hours, 6 hours, 1 day, and 2 days after dosing.
- High dose with and without activation: 2000 mg/kg
- Other: 3 males and 3 females per group were used in this study, but since no relevant differences in toxicity between the sexes were observed, only males were used in the micronucleus assay. Two males and 1 female died in the 1500 mg/kg group, and 3 males and 2 females in the 2000 mg/kg died. Based on these results, the maximum tolerated dose was estimated to be 1000 mg/kg.

RESULTS OF DEFINITIVE STUDY
- Induction of micronuclei (for Micronucleus assay): The test substance did not induce any statistically significant increases in micronucleated PCEs at any dose level examined (250, 500, and 750 mg/kg). The vehicle control group had less than approximately 0.4% micronucleated PCEs and the group mean was within the historical control range. The positive control induced a statistically significant increase in micronucleated PCEs as compared to that of the vehicle control, with means and standard errors of 3.95 +/- 0.33 % and 2.37 +/- 0.32 %, for the initial and repeat micronucleus assays, respectively.
- Ratio of PCE/NCE (for Micronucleus assay): The test substance was not cytotoxic to the bone marrow (i.e., no statistically significant decrease in the PCE:NCE ratio) at any dose level of the test substance.

Toxic Signs: Toxic signs were observed at the 1000 mg/kg dose level including soft feces, hypoactivity, rough haircoat and death at both the 24 and 48 hour timepoints (5 out of 12 died). Based on the high mortality rate, the rest of the animals in this group were euthanized and the bone marrow was not analyzed. One animal at the 500 mg/kg dose developed soft feces, and animals at the 750 mg/kg dose level developed soft feces, hypoactivity, rough haircoats, irregular respiration, and/or recumbency. In addition, one animal died in the 750 mg/kg group.

Conclusions:
The test substance was reported as negative in the mouse bone marrow micronucleus assay, under the conditions of this study.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Justification for classification or non-classification

Sodium tungstate was negative for mutagenicity in an in vitro bacterial reverse mutation assay conducted according to OECD 471, an in vitro chromosome aberration assay conducted according to OECD 473, an in vitro L5178Y TK +/- Mouse Lymphoma Forward Mutation Assay conducted according to OECD 476, and an in vivo micronucleus assay conducted according to OECD 474. Therefore, based on the weight-of-evidence from the available data, sodium tungstate does not warrant classification.