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Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

1. Information on zirconium dioxide
Genetic toxicity in vitro:
One reliable bacterial reverse mutation study is available. The study was performed according to OECD guideline 471 and EU method B13/14. Zirconium dioxide tested negative with and without metabolic activation in Salmonella typhimurium strains.

In vitro cytogenicity in mammalian cells:
One reliable test was performed according to OECD guideline 473. Zirconium dioxide tested negative in cultured peripheral human lymphocytes with and without metabolic activation.

In vitro gene mutation in mammalian cells:
One reliable mouse lymphoma test was performed according to OECD guideline 476. Zirconium dioxide tested negative in mouse lymphoma L5178Y cells with and without metabolic activation.

2. Information on magnesium oxide

Because magnesium oxide transforms to magnesium hydroxide when in contact with moisture (e.g. physiological liquids), data for magnesium hydroxide were added to the weight of evidence approach to cover the endpoint of gene mutation in bacterial cells. The study was performed according to OECD guideline 471 and EU method B13/14. Magnesium hydroxide tested negative with and without metabolic activation in Salmonella typhimurium strains and E. coli WP2 uvr A.


3. Conclusion on magnesium zirconium oxide
Based on the available data on the individual components, magnesium zirconium oxide is not expected to be genotoxic.

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 2010-04-19 to 2010-05-18
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:
yes
Remarks:
In the dose range finding study/first cytogenetic assay during incubation period, temperature was outside the range of 37.0±1.0°C as specified in the protocol with a minimum of 31.3°C for approx 1.5 hour. This deviation had no effects on the results
GLP compliance:
yes
Type of assay:
other: in vitro mammalian chromosome aberration test
Target gene:
Not applicable
Species / strain / cell type:
lymphocytes: cultured peripheral human lymphocytes
Details on mammalian cell type (if applicable):
See section 'Any other information on materials and methods incl. tables'
Additional strain / cell type characteristics:
not specified
Metabolic activation:
with and without
Metabolic activation system:
Rat liver microsomal enzymes were routinely prepared from adult male Wistar rats (6), which were obtained from Charles River (Sulzfeld, Germany) (S9 fraction)
Test concentrations with justification for top dose:
Dose range finding test/first cytogenetic assay: at 3 h exposure time: 10, 33 and 100 µg zirconium dioxide/mL culture medium with and without S9-mix; at 24 and 48 h continuous exposure time blood cultures were treated with 1, 3, 10, 33, 100, 333 and 1000 µg zirconium dioxide/mL culture medium without S9-mix
Second cytogenicity test: without S9-mix: 10, 33 and 100 µg/mL culture medium (24 and 48 h exposure time, 24 h and 48 h fixation time); with S9-mix: 10, 33 and 100 µg/mL culture medium (3 h exposure time, 48 h fixation time)
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO
- Justification for choice of solvent/vehicle: no data
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
mitomycin C
Remarks:
Without metabolic activation (-S9-mix); solvent for positive controls: Hanks' Balanced Salt Solution (HBSS) without calcium and magnesium
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
cyclophosphamide
Remarks:
With metabolic activation (+S9-mix); solvent for positive controls: Hanks' Balanced Salt Solution (HBSS) without calcium and magnesium
Details on test system and experimental conditions:
METHOD OF APPLICATION: in medium

DURATION
- Preincubation period: not applicable
- Exposure duration: 24 and 48 h in the absence of S9-mix or for 3 h in the presence of S9 mix (second cytogenetic assay)
- Expression time (cells in growth medium): after 3 h exposure, the cells exposed to zirconium dioxide in the presence of S9-mix were separated from the exposure medium by centrifugation (5 min, 365 g). The supernatant was removed and the cells were rinsed once with 5 mL of HBSS and incubated in 5 mL culture medium for another 44-46 h; the cells that were treated for 24 h and 48 h in the absence of S9-mix were not rinsed after exposure but were fixed immediately after 24 h and 48 h (24 h and 48 h fixation time)
- Selection time (if incubation with a selection agent): not applicable
- Fixation time (start of exposure up to fixation or harvest of cells): see above

SELECTION AGENT (mutation assays): not applicable
SPINDLE INHIBITOR (cytogenetic assays): colchicine (0.5 µg/mL medium) (Acros Organics, Belgium) - during the last 2.5-3 h of the culture period
STAIN (for cytogenetic assays): Cell cultures were centrifuged for 5 min at 1300 rpm (365 g) and the supernatant was removed. Cells in the remaining cell pellet were swollen by a 5 min treatment with hypotonic 0.56% (w/v) potassium chloride (Merck) solution at 37°C. After hypotonic treatment, cells were fixed with 3 changes of methanol (Merck): acetic acid (Merck) fixative (3:1 v/v). Fixed cells were dropped onto cleaned slides, which were immersed in a 1:1 mixture of 96% (v/v) ethanol (Merck)/ether (Merck) and cleaned with a tissue. The slides were marked with the NOTOX study identification number and group number. At least two slides were prepared per culture. Slides were allowed to dry and thereafter stained for 10-30 min with 5% (v/v) Giemsa (Merck) solution in tap water. Thereafter slides were rinsed in tap-water and allowed to dry. The dry slides were cleared by dipping them in xylene (Klinipath, Duiven, The Netherlands) before they were embedded in Pertex (Klinipath) and mounted with a coverslip.

NUMBER OF REPLICATIONS: duplicate cultures

NUMBER OF CELLS EVALUATED: To prevent bias, all slides were randomly coded before examination of chromosome aberrations and scored. An adhesive label with NOTOX study identification number and code was placed over the marked slide. One hundred metaphase chromosome spreads per culture were examined by light microscopy for chromosome aberrations. in case the number of aberrant cells, gaps excluded, was > or = 25 in 50 metaphases, no more metaphases were examined. Only metaphases containing 46 ± 2 centromeres (chromosomes) were analysed. The number of cells with aberrations and the number of aberrations were calculated.

DETERMINATION OF CYTOTOXICITY
- Method: mitotic index: The mitotic index of each culture was determined by counting the number of metaphases per 1000 cells. At least three analysable concentrations were used for scoring of the cytogenetic assay. The highest concentration analysed was based on the solubility of zirconium dioxide in the culture medium. However, the extent of precipitation may not interfere with the scoring of chromosome aberrations.

OTHER EXAMINATIONS:
- Determination of polyploidy: yes
- Determination of endoreplication: yes
- Other: no

OTHER: Test substance preparation: Zirconium dioxide was suspended in dimethyl sulfoxide of spectroscopic quality (SeccoSolv, Merck, Darmstadt, Germany) at concentrations of 0.3 mg/mL and above. the stock solution was treated with ultrasonic waves to obtain a homogeneous suspension. Zirconium dioxide was dissolved in dimethyl sulfoxide at concentrations of 0.1 mg/mL and below. Zirconium dioxide concentrations were used within 2.5 hours after preparation. The final concentration of the solvent in the culture medium was 1.0% (v/v)
Evaluation criteria:
A test substance was considered positive (clastogenic) in the chromosome aberration test if:
a) It induced a dose-related statistically significant (Chi-square test, one-side, p < 0.05) increase in the number of cells with chromosome aberrations.
b) A statistically significant and biologically relevant increase in the frequencies of the number of cells with chromosome aberrations was observed in the absence of a clear dose-response relationship.
A test substance was considered negative (not clastogenic) in the chromosome aberration test if none of the tested concentrations induced a statistically significant (Chi-square test, one-sided, p < 0.05) increase in the number of cells with chromosome aberrations. The preceding criteria are not absolute and other modifying factors might enter into the final evaluation decision.
Statistics:
The incidence of aberrant cells (cells with one or more chromosome aberrations, gaps included or excluded) for each exposure group outside the laboratory historical control data range was compared to that of the solvent control using Chi-square statistics:
X²=[(N-1) (ad-bc)²]/[(a+b) (c+d) (a+c) (b+d)]
where b = the total number of aberrant cells in the control cultures, d = the total number of non aberrant cells in the control cultures, n0 = the total number of cells scored in the control cultures, a = the total number of aberrant cells in treated cultures to be compared with the control, c = the total number of non aberrant cells in treated cultures to be compared with the control, n1 = the total number of cells scored in the treated cultures, N = sum of n0 and n1
If P [X² > [(N-1) (ad-bc)²]/[(a+b) (c+d) (a+c) (b+d)]] (one-tailed) is small (p< 0.05) the hypothesis that the incidence of cells with chromosome aberrations is the same for both the treated and the solvent control group is rejected and the number of aberrant cells in the test group is considered to be significantly different from the control group at the 95% confidence interval.
Key result
Species / strain:
lymphocytes: cultured peripheral human lymphocytes
Remarks:
all strains/cell types tested
Metabolic activation:
without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Remarks:
The mitotic index of the test substance didn't reach 50% of the control value for all tested concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
lymphocytes: cultured peripheral human lymphocytes
Remarks:
all strains/cell types tested
Metabolic activation:
with
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Remarks:
The mitotic index of the test substance didn't reach 50% of the control value for all tested concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
TEST-SPECIFIC CONFOUNDING FACTORS
- Effects of pH: no data
- Effects of osmolality: no data
- Evaporation from medium: no data
- Water solubility: no data
- Precipitation: yes

RANGE-FINDING/SCREENING STUDIES: In order to select the appropriate dose levels for the chromosome aberration test cytotoxicity data were obtained in a dose range finding test. Zirconium dioxide was tested in the absence and presence of 1.8% (v/v) S9-fraction. Lymphocytes (0.4 mL blood of a healthy male donor + 5 mL or 4.8 mL culture medium + (+ or - S9) + 0.1 mL (9 mg/mL) Phytohaemagglutinin) were cultured for 48 h and thereafter exposed to selected doses of zirconium dioxide for 3h, 24h, and 48h in the absence of S9-mix or for 3 h in the presence of S9-mix. The highest tested concentration was determined by the solubility of zirconium dioxide in the culture medium at the 3h exposure time. At a concentration of 100 µg/mL zirconium dioxide precipitated in the culture medium. The lymphocytes were cultured in duplicate at the 3 h exposure time and appropriate vehicle and positive controls were included. At the 24h and 48h exposure time, zirconium dioxide was tested beyond the limit of solubility to obtain adequate toxicity data. After 3 h exposure to zirconium dioxide in the absence or presence fo S9-mix, the cells were separated from the exposure medium by centrifugation (5 min, 365 g). The supernatant was removed and cells were rinsed with 5 mL HBSS. After a second centrifugation step, HBSS was removed and cells were resuspended in 5 mL culture medium and incubated for another 20 - 22 h (24 h fixation time). The cells that were exposed for 24 h and 48 h in the absence of S9-mix were not rinsed after exposure but were fixed immediately (24 and 48h fixation time).Cytotoxicity of zirconium dioxide in the lymphocyte cultures cultures was determined using the mitotic index. No cytotoxicity was observed in the duplicate cultures of the 3 h exposure time and the slides were scored for chromosome aberrations. The first cytogenetic assay was ommited. Based on the results of the dose range finding test an appropriate range of dose levels was chosen for the second cytogenetic assay considering the highest dose level was determined by the solubility.

COMPARISON WITH HISTORICAL CONTROL DATA: The number of cells with chromosome aberrations found in the solvent control cultures was within the laboratory historical control data range. The number of polyploid cells and cells with endoreduplicated chromosomes in the solvent control cultures was within the laboratory historical control data range. The positive control chemicals (MMC-C and CP) both produced statistically significant increases in the mutation frequency of aberrant cells. It was therefore concluded that the test conditions were adequate and that the metabolic activation system (S9-mix) functioned properly.

ADDITIONAL INFORMATION ON CYTOTOXICITY:

Results:

Both in the absence and presence of S9-mix zirconium dioxide did not induce a statistically significant or biologically relevant increase in the number of cells with chromosome aberrations in two independent experiments.

No effects of zirconium dioxide on the number of polyploid cells and cells with endoreduplicated chromosomes were observed both in the absence and presence of S9-mix. Therefore it can be concluded that zirconium dioxide does not disturb mitotic processes and cell cycle progression and does not induce numerical chromosome aberrations under the experimental conditions of this test.

Table 1: Mitotic index of human lymphocyte cultures treated with zirconium dioxide at the 24 h and 48 h continuous exposure time in the dose range finding test.

 Zirconium dioxide concentration (µg/mL)  Number of metaphases per 1000 cells   
   Absolute Percentage of control 
 Without metabolic activation (-S9 -mix)    
 24 h exposure time, 24 h fixation time    
 Control a)  36  100
 1  33  92
 3  32  89
 10  31  86
 33  36  100
 100 b)  34  94
 333 c)  38  106
 1000 c)  38  106
 48 h exposure time, 48 h fixation time    
 Control a)  42  100
 1  44  105
 3  44  105
 10  42  100
 33  39  93
 100 b)  42  100
 333 c)  44  105
 1000 c)  44  105

a) Dimethyl sulfoxide

b) Zirconium dioxide precipitated in the culture medium

c) Zirconium dioxide precipitated heavily in the culture medium which would interfere with the scoring of chromosome aberrations

Table 2: Mitotic index of human lymphocyte cultures treated with zirconium dioxide at the 3 h exposure time in the dose range finding test (first cytogenetic assay)

 Zirconium dioxide concentration (µg/mL)  Number of metaphases per 1000 cells   
 Without metabolic activation (-S9 -mix)  Absolute Percentage of control 
 3 h exposure time, 24 h fixation time    
 Control b)  46 - 51  100
 10  48 - 50  101
 33  47 - 49  99
 100  51 - 53  107
 MMC-C; 0.5 µg/mL  38 - 33  73
 With metabolic activation (+ S9 -mix)    
 Control b)  54 -54  100
 10  50 - 49  92
 33  55 - 54  101
 100 c)  50 - 53  95
 CP; 10 µg/mL  21 - 28  45

a) Duplicate cultures

b) Dimethyl sulfoxide

c) Zirconium dioxide precipitated in the culture medium

Table 3: Mitotic index of human lymphocyte cultures treated with zirconium dioxide in the second cytogenetic assay

 Zirconium dioxide concentration (µg/mL)  Number of metaphases per 1000 cells   
   Absolute Percentage of control 
 Without metabolic activation (-S9 -mix)    
 24 h exposure time, 24 h fixation time    
 Control b)  65 -68  100
 10  63 - 69  99
 33  60 65  94
 100 c)  58 -61  89
 MMC-C; 0.2 µg/mL  31 - 35  50
 48 h exposure time, 48 h fixation time    
 Control b)  71 - 68  100
 10  65 - 69  96
 33  68 - 66  96
 100 c)  62 - 60  88
 MMC-C; 0.1 µg/mL  53 - 55  78
 With metabolic activation (+S9 -mix)    
 3 h exposure time, 48 h fixation time    
 Control b)  75 - 77  100
 10  72 - 76  97
 33  79 - 79  104
100   78 - 75  101
 CP; 10 µg/mL  28 - 25  d)

a) Duplicate cultures

b) Dimethyl sulfoxide

d) Zirconium dioxide precipitated in the culture medium

e) CP was fixed after 24 hours. Therefore, the mitotic index could not be calculated as percentage of control.

Conclusions:
Interpretation of results: negative with and without metabolic activation

Finally, it is concluded that this test is valid and that zirconium dioxide is not clastogenic in human lymphocytes under the experimental conditions of this test.
Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
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:
Deviations of temperature and humidity caused by adjustment after opening of the incubator door. However the study integrity was not adversely affected by the deviations
Qualifier:
according to guideline
Guideline:
EU Method B.17 (Mutagenicity - In Vitro Mammalian Cell Gene Mutation Test)
Deviations:
yes
Remarks:
Deviations of temperature and humidity caused by adjustment after opening of the incubator door. However the study integrity was not adversely affected by the deviations
GLP compliance:
yes (incl. QA statement)
Remarks:
Food and Consumer Product Safety Authority (VWA), Prinses Beatrixlaan 2, 2595 AL Den Haag, Postbus 19508, 2500,CM Den Haag, The Netherlands
Type of assay:
other: mammalian cell gene mutation assay
Target gene:
thymidine-kinase (TK) locus L5178Y
Species / strain / cell type:
mouse lymphoma L5178Y cells
Details on mammalian cell type (if applicable):
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: no data
- Periodically checked for karyotype stability: no data
- Periodically "cleansed" against high spontaneous background: no data
Additional strain / cell type characteristics:
not specified
Metabolic activation:
with and without
Metabolic activation system:
rat liver S9-mix induced by a combination of phenobarbital and beta-naphtoflavone
Test concentrations with justification for top dose:
0.03, 0.1, 1, 3, 10, 33 and 100 µg/mL
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO
- Justification for choice of solvent/vehicle: no data
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
methylmethanesulfonate
Remarks:
Without metabolic activation; MMS was dissolved in dimethyl sulfoxide. The stock solutions of MMS were prepared immediately before use.
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
cyclophosphamide
Remarks:
With metabolic activation; CP was dissolved in Hanks' balanced salt solution (HBSS) without calcium and magnesium. The stock solutions of CP were stored in aliquots at < or = -15°C in the dark and one sample was thawed immediately before use.
Details on test system and experimental conditions:
In a first experiment, cell cultures were exposed for 3 hours to zirconium dioxide in exposure medium in the absence and presence of S9-mix. In a second experiment, cell cultures were exposed to zirconium dioxide in exposure medium for 24 hours in the absence of S9-mix and for 3 hours in the presence of S9-mix.

METHOD OF APPLICATION: in medium

DURATION
- Preincubation period: not applicable
- Exposure duration: 3 hours or 24 hours
- Expression time (cells in growth medium): 48 hours
- Selection time (if incubation with a selection agent): 11 or 12 days (TFT selection)
- Fixation time (start of exposure up to fixation or harvest of cells): 2 hours (MTT staining)

SELECTION AGENT (mutation assays): TFT
SPINDLE INHIBITOR (cytogenetic assays): not applicable
STAIN (for cytogenetic assays): not applicable

NUMBER OF REPLICATIONS: 2 independent experiments

NUMBER OF CELLS EVALUATED: for the determination of mutation frequency a total number of 9.6 x 1E05 cells/concentration were plated in five 96-well microtiter plates, each well containing 2000 cells in selective medium, with the exception of the positive control groups (MMS and CP) where a total number of 9.6 x 1E05 cells/concentration were plated in ten 96-well microtiter plates, each well containing 1000 cells in selective medium (trifluorothymidine-selection).

DETERMINATION OF CYTOTOXICITY
- Method: cloning efficiency

OTHER:
- Determination of polyploidy: not applicable
- Determination of endoreplication: not applicable
- Type and identity of media: horse serum was inactivated by incubiation at 56°C for at least 30 minutes. Basic medium: RPMI 1640 Hepes buffered medium (Dutch modificiation) containing penicillin/streptomycin (50 U/mL and 50 µg/mL, respectively), 1 mM sodium pyruvate and 2 mM L-glutamin. Growth medium: basic medium, supplemented with 10% (v/v) heat-inactivated horse serum (=R10 medium). Exposure medium: for 3 hour exposure: cells were exposed to the test substance in basic medium supplemented with 5% (v/v) heat-inactivated horse serum (R5-medium). For 24 hour exposure: cells were exposed to the test substance in basic medium supplemented with 10% (v/v) heat-inactivated horse serum (R10-medium). Selective medium consisted of basic medium supplemented with 20% (v/v) heat-inactivated horse serum (total amount of serum = 20%, R20) and 5 µg/mL trifluorothymidine (TFT) (Sigma). Non-selective medium consisted of basic medium supplemented with 20% (v/v) heat-inactivated horse serum (total amount of serum = 20%, R20).
- State of the suspension/solution according to the concentration: at a concentration of 0.12 mg/mL and higher zirconium dioxide was suspended in dimethyl sulfoxide (DMSO, SeccoSolv, Merck Darmdstadt, Germany). At a concentration of 0.04 mg/mL and lower the test substance was dissolved in dimethyl sulfoxide. The stock solution was treated with ultrasonic waves to obtain a homogeneous suspension. Zirconium dixoide concentrations were used within 1 hour after preparation. The final concentration of the solvent in the exposure medium was 0.8% (v/v).
Evaluation criteria:
The global evaluation factor (GEF) has been defined as the mean of the negative/solvent mutation frequency distribution plus one standard deviation. For the micro well version of the assay the GEF is 126. A test substance is considered positive (mutagenic) in the mutation assay if it induces a mutation frequency of more then mutation frequency (controls) + 126 in a dose-dependent manner. An observed increase should be biologically relevant and will be compared with the historical control data range. A test substance is considered equivocal (questionable) in the mutation assay if no clear conclusion for positive or negative result can be made after an additional confirmation study. A test substance is considered negative (not mutagenic) in the mutation assay if: a) non of the tested concentrations reaches a mutation frequency of mutation frequency (controls) + 126; b) the results are confirmed in an independent repeated test.
Key result
Species / strain:
mouse lymphoma L5178Y cells
Remarks:
all strains/cell types tested
Metabolic activation:
with and without
Genotoxicity:
negative
Remarks:
first and second experiment
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
TEST-SPECIFIC CONFOUNDING FACTORS
- Effects of pH:no data
- Effects of osmolality: no data
- Evaporation from medium: no data
- Water solubility: no data
- Precipitation: Zirconium dioxide precipitated in the exposure medium at concentration of 100 µg/mL and above. Zirconium dioxide was tested beyond the limit of solubility to obtain adequate cytotoxicity data, the concentration used as the highest test substance concentration for the dose range finding test was 333 µg/mL
- Other confounding effects: no data

RANGE-FINDING/SCREENING STUDIES: L5178Y mouse lymphoma cells were treated with a test substance concentration range of 3 to 333 µg/mL in the absence of S9-mix with a 3 and 24 hour treatment period and in the presence of S9-mix with a 3 hour treatment period. After 3 hours of treatment: both in the absence and presence of S9-mix, no toxicity in the relative suspension growth was observed up to and including the highest test substance concentration of 333 µg/mL compared to the suspension growth of the solvent control. After 24 hours of treatment with various concentrations of Zirconium dioxide, no toxicity in the relative suspension growth was observed up to and including the highest test substance concentration of 333 µg/mL compared to the suspension growth of the solvent control.

COMPARISON WITH HISTORICAL CONTROL DATA: The spontaneous mutation frequencies in the solvent-treated control cultures were between the minimum and maximum value of the historical control data range.

ADDITIONAL INFORMATION ON CYTOTOXICITY: No toxicity was observed and all dose levels were evaluated in the absence and presence of S9-mix.

The growth rate over the two-day expression period for cultured treated with DMSO was between 20 and 28 (3 hours treatment) and 40 and 50 (24 hours treatment).

Mutation frequencies in cultures treated with positive control chemicals were increased by 26- and 14-fold for MMS in the absence of S9-mix, and by 19-fold for CP in the presence of S9-mix, in the first and second experiment respectively. It was therefore concluded that the test conditions, both in the absence and presence of S9-mix, were appropriate for the detection of a mutagenic response and that the metabolic activation system (S9-mix) functioned properly. In addition the observed mutation frequencies of the positive control substances were within the acceptability criteria of this assay.

Experiment 1: Cytotoxic and mutagenic response of zirconium dioxide in the mouse lymphoma L5178Y test system (3 hours treatment)

Without metabolic activation

 dose (µg/mL) RSG (%) CE day2 (%)  RS day2 (%)  RTG (%)  Mutation frequency x 1E-06      
           total  (small  large)
 SC1  100  118  100  100  53  31  20
 SC2  100  113  100  100  51  31  19
0.03   112  101  87  98  50  23  25
 0.1  105  110  95  100  54  29  23
 0.3  110  94  81  90  54  26  26
 1  117  111  96  113  50  21  28
 3  112  101  87  97  49  25  22
 10  106 98   85  90  58  34  23
 33  102  97  84  85  58  30 27 
 100 (1)  103  105  91  94  52  29  22
 MMS  66  57  49  32  1334  804  318

With 8% (v/v) metabolic activation

 dose (µg/mL)  RSG (%)  CE day2 (%)  RS day2 (%)  RTG (%)  Mutation frequency x 1E-06      
         total (small  large) 
 SC1  100  88  100  100  54  32  21
 SC2  100  89  100  100  53  29  23
 0.03  100  102  116  116  53  34  18
 0.1  99  83  94  93  54  38  15
 0.3  99  79  90  89  59  32  26
 1  100  81  92  93  67  33 33 
 3  92  74  83  77  78  47  29
 10  99  86  98  97  60  31  27
 33  92  90  102  94  56  33  21
100 (1)  100  77  87  87  61  32  28
 CP  53  72  82  44  1000  674  191

 

Note: all calculations were made without rounding off

RSG = Relative Suspension Growth; CE = Cloning efficiency; RS = Relative Survival; RTG = Relative Total Growth; SC = Solvent Control = DMSO; MMS = Methylmethanesulfonate; CP = cyclophosphamide

(1) zirconium dioxide precipitated in the exposure medium

Experiment 2: Cytotoxic and mutagenic response of zirconium dioxide in the mouse lymphoma L5178Y test system (24 hours)

Without metabolic activation

dose (µg/mL)   RSG (%)  CE day2 (%)  RS day2 (%)  RTG (%)  Mutation frequency x 1E-06      
           total  (small  large)
 SC1  100  118  100  100  57  32  23
 SC2  100  104 100   100  63  36  25
 0.03  120  88  79  95 72   43  27
 0.1  127  107  96  122  66  34  29
 0.3  137  120  108  148  50  29  20
1   127  111  100  128  54  34  18
 3  139  110  99  138  55  37  17
 10  140  91  82  115  80  48  29
 33  138  115  103  143  69  41  25
 100 (1)  153  97  87  133  54  38  15
 MMS  119 77   69  83  815  564 157 

With 12% (v/v) metabolic activation:

 dose (µg/mL)  RSG (%)  CE day2 (%)  RS day2 (%)  RTG (%)  Mutation frequency x 1E-06      
           total  (small large)
 SC1  100  111  100  100  67  40  25
 SC2  100  80  100  100  85  44  37
 0.03  107  77  80  86  85  57  26
 0.1  97  86  90  87  86  45  37
 0.3  99  102  107  105  64  34  28
 1  97  107  111  108  69  43  24
 3  99  97  101  100  75  53 20 
 10  90  99  104  93  77  54  20
33  89  107  111  99  94  49  40
 100 (1)  91  102  107  97  71  45  24
 CP  42  54  56  24  1422  832  355

(1) = Zirconium dioxide precipitated in the exposure medium

Note: all calculations were made without rounding off

RSG = Relative Suspension Growth; CE = Cloning efficiency; RS = Relative Survival; RTG = Relative Total Growth; SC = Solvent control = DMSO; MMS = Methylmethanesulfonate; CP = Cyclophosphamid (1) = Zirconium dioxide precipitated in the exposure medium

Conclusions:
Interpretation of results: negative with and without metabolic activation

In conclusion, zirconium dioxide is not mutagenic in the TK mutation test system under the specified experimental conditions.
Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
25-02-2010 to 11-03-2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)
Deviations:
no
GLP compliance:
yes
Type of assay:
bacterial reverse mutation assay
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:
rat liver microsomal enzymes were routinely prepared from adult male Wistar rats
Test concentrations with justification for top dose:
In the dose range finding test, magnesium hydroxide was tested up to concentrations of 5000 µg/plate. Based on the results, magnesium hydroxide was tested in the first mutation assay at a concentration range of 100 to 5000 µg/plate. In an independent repeat of the assay, magnesium hydroxide was tested at the same concentration range as in the first assay.
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
Remarks:
dimethyl sulfoxide
Positive controls:
yes
Positive control substance:
not specified
Details on test system and experimental conditions:
Test system: Salmonella typhimurium bacteria and Escherichia coli bacteria.
The Salmonella typhimurium strains were regularly checked to confirm their histidine-requirement, crystal violet sensitivity, ampicillin resistance (TA98 and TA100), UV-sensitivity and the number of spontaneous revertants.
The Escherichia coli WP2uvrA strain was regularly checked to confirm the tryptophan-requirement, UV-sensitivity and the number of spontaneous revertants.
Stock cultures of the five strains were stored in liquid nitrogen (-196°C).
Evaluation criteria:
No formal hypothesis testing was done.

A test substance is considered negative (not mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 is not greater than two (2) times the concurrent control, and the total number of revertants in tester strains TA1535, TA1537, TA98 or WP2uvrA is not greater than three (3) times the concurrent control.
b) The negative response should be reproducible in at least one independently repeated experiment.

A test substance is considered positive (mutagenic) in the test if:
a) The total number of revertants in tester strain TA100 is greater than two (2) times the concurrent control, or the total number of revertants in tester strains TA1535, TA1537, TA98 or WP2uvrA is greater than three (3) times the concurrent control.
b) In case a repeat experiment is performed when a positive response is observed in one of the tester strains, the positive response should be reproducible in at least one independently repeated experiment.

The preceding criteria were not absolute and other modifying factors might enter into the final evaluation decision.
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
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
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
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid

Dose range finding test

Magnesium hydroxide was tested in the tester strains TA100 and WP2uvrA with concentrations of 3, 10, 33, 100, 333, 1000, 3330, and 5000 µg/plate in the absence and presence of S9-mix.

Table 1. Strain TA100 - Without S9 -mix

 Plate

Dose (micrograms/plate)

1 

2 

3 

Mean 

SD 

 Positive control

1039

990 

983 

1004 ±

31 

 Solvent control

99

94

112

102 ±

9

 3

95 

87 

85 

89 ±

5 

 10

84

101

86

90 ±

9 

 33

123

139

107 

123 ±

16

 100

106

100

94

100 ±

6

 333

111

110 

108

110 ±

2

 1000

87

95

109

97 ±

11 

 3330

84

106

84

91 ±

13 

 5000

175

111

101 

129 ±

40

Table 2. Strain TA100 With S9 -mix

 Plate

Dose (micrograms/plate)

1 

2 

3 

Mean 

SD 

 Positive control

1283 

1347 

1240 

1290±  

 54

Solvent control 

156 

134 

126 

139±  

16 

3 

96 

65 

66 

76±  

18 

10 

71 

83 

95 

83±  

12 

33 

84 

80 

112 

92±  

17 

100 

95 

107 

99 

100±  

6 

333 

107 

99 

93 

100±  

7 

1000 

102 

86 

94 

94±  

8 

3330 

108 

100 

97 

102±  

6
5000  95  139  105  113±  23

No precipitation of magnesium hydroxide was observed on the plates at start or end of incubation period.

No reduction of the bacterial lawn and no biologically relevant decrease in the number of revertants were observed.

No increase in the number of revertants was observed upon treatment with magnesium hydroxide under all conditions tested.

Mutation assay

Magnesium hydroxide was tested in the absense and presence of S9-mix in two mutation assays. The first experiment was performed with the strains TA1535, TA1537 and TA98 and the second experiment was performed with strains TA1535, TA1537, TA98, TA100 and WP2uvrA. Results are in the tables below.

Table 3. Experiment 1: Mutagenic response of magnesium hydroxide in Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

 Dose

(µg/plate)

 Mean number of revertant colonies/3 replicate plates (± S.D.) with different strains of Salmonella typhimurium and one Escherichia coli strain

 TA1535

TA1537 

TA98 

TA100 

 WP2uvrA

 Without S9-mix

 positive control

857 ± 14 

343 ± 11 

982 ± 89 

1004 ± 31 

513 ± 1

 solvent control

6 ± 2

3 ± 1 

12 ± 1 

102 ± 9 

21 ± 4 

 

 

 

 

 

 

 3

 

 

 

89 ± 5 

19 ± 5 

10 

 

 

 

90 ± 9 

18 ± 3 

33 

 

 

 

123 ± 16 

23 ± 2 

100 

7 ± 2 

3 ± 1 

16 ± 3 

100 ± 6 

16 ± 6 

333 

6 ± 1 

3 ± 1 

12 ± 1 

110 ± 2 

20 ± 2 

1000 

5 ± 1 

4 ± 1 

14 ± 5 

97 ± 11 

18 ± 4 

3330 

7 ± 1 

4 ± 2 

14 ± 1 

91 ± 13 

24 ± 7 

5000 

8 ± 1 

3 ± 0 

16 ± 3 

129 ± 40 

25 ± 3 

 With S9-mix

 positive control

155 ± 11 

300 ± 31 

 940 ± 21

1290 ± 54 

282 ± 20 

solvent control 

6 ± 1 

3 ± 0 

17 ± 3 

139 ± 16 

17 ± 5 

 

 

 

 

 

 

3 

 

 

 

76 ± 18 

18 ± 2 

10 

 

 

 

83 ± 12 

18 ± 5 

33 

 

 

 

92 ± 17 

17 ± 3 

100 

 8 ± 1

3 ± 0 

21 ± 7 

100 ± 6 

16 ± 4 

333 

6 ± 3 

4 ± 1 

17 ± 1

100 ± 7 

23 ± 2 

1000 

6 ± 2 

3 ± 1 

14 ± 4 

94 ± 8 

19 ± 5 

3330 

7 ± 1 

3 ± 0 

17 ± 3 

102 ± 6 

23 ± 3 

5000 

8 ± 2 

5 ± 1 

13 ± 1 

113 ± 23 

23 ± 3 

Table 4. Experiment 2: Mutagenic response of magnesium hydroxide in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

 

Dose (µg/plate)

Mean number of revertant colonies/3 replicate plates (± S.D.) with different strains of Salmonella typhimurium and one Escherichia coli strain 

 TA1535

TA1537 

TA98 

TA100 

 WP2uvrA

 Without S9-mix

positive control

735 ± 16

312 ± 40 

1109 ± 31 

958 ± 24

952 ± 27 

solvent control 

9 ± 2 

3 ± 0 

18 ± 3 

104 ± 6 

19 ± 4 

 

 

 

 

 

 

100 

9 ± 2 

3 ± 1 

15 ± 2 

96 ± 6 

21 ± 3 

333 

8 ± 1 

3 ± 0 

16 ± 5 

106 ± 13 

21 ± 3 

1000 

6 ± 1 

6 ± 1 

19 ± 4 

98 ± 4 

21 ± 3 

3330 

7 ± 1 

3 ± 1 

15 ± 4 

101 ± 6 

24 ± 3 

5000 

7 ± 3 

3 ± 0 

14 ± 3 

103 ± 10 

22 ± 4 

With S9-mix 

 positive control

125 ± 18 

368 ± 8 

669 ± 33 

745 ± 48 

176 ± 18 

solvent control 

4 ± 1 

3 ± 0 

19 ± 2 

61 ± 2 

20 ± 4 

 

 

 

 

 

100 

7 ± 4 

3 ± 1 

18 ± 1 

66 ± 5 

20 ± 4 

333 

7 ± 1 

3 ± 0 

22 ± 4 

68 ± 3 

21 ± 4 

1000 

6 ± 2 

3 ± 1 

21 ± 3 

65 ± 7 

18 ± 2

3330 

7 ± 2 

3 ± 0 

19 ± 4 

80 ± 6 

30 ± 5 

5000 

7 ± 3 

4 ± 2 

19 ± 3 

105 ± 6 

28 ± 2

Precipitation of magnesium hydroxide on the plates was not observed at the start or at the end of the incubation period.

In both mutation assays, there was no reduction of the bacterial background lawn and no biologically relevant decrease in the number of revertants at any of the concentrations tested in all tester strains in the absence and presence of S9-mix.

In both assays, no increase in the number of revertants was observed upon treatment with magnesium hydroxide under all conditions tested.

Conclusions:
All bacteria strains showed negative responses over the entire dose range, i.e. no significant dose-related increase in the number of revertants in two repeated experiments.
The negative strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.
Based on the results of this study it is concluded that magnesium hydroxide is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.
Executive summary:

Evaluation of the mutagenic activity of magnesium hydroxide in the Salmonella typhimurium reverse mutation assay and the Escherichia coli reverse mutation assay (with independent repeat).

 

Magnesium hydroxide was tested in the Salmonella typhimurium reverse mutation assay with four histidine-requiring strains of Salmonella typhimurium (TA1535, TA1537, TA98 and TA100) and in the Escherichia coli reverse mutation assay with a tryptophan-requiring strain of Escherichia coli (WP2uvrA). The test was performed in two independent experiments in the presence and absence of S9-mix (rat liver S9-mix induced by a combination of phenobarbital and β-naphthoflavone).

 

The study procedures described in the report were based on the most recent OECD and EC guidelines.

 

In the dose range finding test, magnesium hydroxide was tested up to concentrations of 5000 µg/plate in the absence and presence of S9-mix in the strains TA100 and WP2uvrA. Magnesium hydroxide did not precipitate on the plates at this dose level. The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed. Results of this dose range finding test were reported as part of the first experiment of the mutation assay.

 

Based on the results of the dose range finding test, magnesium hydroxide was tested in the first mutation assay at a concentration range of 100 to 5000 µg/plate in the absence and presence of 5% (v/v) S9-mix in tester strains TA1535, TA1537 and TA98. In an independent repeat of the assay with additional parameters, magnesium hydroxide was tested at the same concentration range as the first assay in the absence and presence of 10% (v/v) S9-mix in tester strains TA1535, TA1537, TA98, TA100 and WP2uvrA. The bacterial background lawn was not reduced at any of the concentrations tested and no biologically relevant decrease in the number of revertants was observed.

 

Magnesium hydroxide did not induce a significant dose-related increase in the number of relevant (His+) colonies in tester strain WP2uvrA both in the absence and presence of S9-metabolic activation. The results were confirmed in an independently repeated experiment.

 

In this study, the negative and strain-specific positive control values were within the laboratory historical control data ranges indicating that the test conditions were adequate and that the metabolic activation system functioned properly.

 

Based on the results of this study it is concluded that magnesium hydroxide is not mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay.

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2008-03-04 to 2008-04-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
Certificate provided by Rheinlandpfalz
Type of assay:
bacterial reverse mutation assay
Species / strain / cell type:
S. typhimurium, other: TA97a, TA98, TA100, TA102, TA1535
Metabolic activation:
with and without
Metabolic activation system:
S9
Test concentrations with justification for top dose:
4998, 1499, 500, and 50 µg/plate - Experiment one
4998, 2499, and 1250 µg/plate - Experiment two
As the test item was not soluble in any suitable solvent, a stock suspension containing 50 g/L was prepared and diluted as necessary.
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO; water
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 4-Nitro-1,2-phenylene diamine in DMSO (without at 80 µg for strains TA 97a, TA98 and TA102); Sodium azide in deionised water (without at 6 µg for strains TA100 and TA1535)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: Benzo-a-pyrene; 2-Amino-anthracene in DMSO (with at 40 µg for stain TA98); 2-Aminoanthracene in DMSO (with at 3 µg for strains TA97a, TA100, TA102 and TA1535)
Details on test system and experimental conditions:
METHOD OF APPLICATION:

- In agar (plate incorporation) - Experiment one
Per strain and dose, four plates with and four plates without S9 mix were used. 10 mL of the test solution of the appropriate concentration were membrane filtrated (size of pores was 0.2 µm) into sterile vessels. Top agar basis was melted in a microwave oven, after melting, 10 mL of histidine-biotin-solution 0.5 mmol per 100 mL basis was added and the bottle was placed in the water bath at 45 degrees C.
0.1 mL of the appropriate solution of the test item was given into a sterile tube. After mixing with 0.1 mL overnight culture of the respective strain and 0.5 mL phosphate buffer (only for treatments without S9) or 0.5 mL S9 mix, 2 mL Top-Agar were added. The mixture was gently vortexed, then poured on a minimal glucose plate and distributed evenly, using a Drigalski spatula. The plates were closed, covered with brown paper and left to harden for a few minutes, then inverted and placed in the dark incubator at 37 degrees C.

- Pre-incubation - Experiment two
Per strain and dose, four plates with and four plates without S9 mix were used. 10 mL of the test solution of the appropriate concentration were membrane filtrated into sterile vessels. Top agar basis was melted in a microwave oven, after melting, 10 mL of histidine-biotin-solution 0.5 mmol per 100 mL basis was added and the bottle was placed in the water bath at 45 degrees C.
0.1 mL of the appropriate solution of the test item was given into a sterile tube. After mixing with 0.1 mL overnight culture of the respective strain, 0.5 mL phosphate buffer (only for treatments without S9) or 0.5 mL S9 mix were added. The mixture was incubated in an incubation chamber at 37 degrees C for 20 minutes. During this time the vessels were aerated through careful shaking. Then 2 mL top agar was added. The mixture was vortexed gently, then poured on a minimal glucose plate and distributed evenly, using a Drigalski spatula. The plates were closed, covered with brown paper and left to harden for a few minutes, then inverted and placed in the dark incubator at 37 degrees C.

DURATION
- Pre-incubation period: 20 minutes at 37 degrees C
- Exposure duration: 48 hours at 37 degrees C - Both experiments

NUMBER OF REPLICATIONS: 4

NUMBER OF CELLS EVALUATED: at least 10^9 cells/mL correlating to 100 colonies / plate
Evaluation criteria:
A test substance is considered to have mutagenic potential, if a significant, reproducible increase of revertant colonies per plate (increase factor >/= 2) in at least one strain can be observed. A concentration-related increase over the range tested can also be taken as a sign of mutagenic activity.
Statistics:
The colonies were counted visually, the numbers were recorded. A spreadsheet software (Microsoft Excel) was used to calculate mean values and standard deviations as well as the increase factor of revertant induction.
Species / strain:
S. typhimurium, other: TA97a, TA98, TA100, TA102, TA1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
- The test item did not show mutagenic effects in both experiments. The number of revertant colonies was not increased in comparison with the spontaneous revertants (solvent only).

- Cytotoxicity of the test item was not detected. The background lawn was visible and the number of revertants was not significantly decreased.

- No toxicity was observed


Remarks on result:
other: all strains/cell types tested

Mean Revertants First Experiment:

Strain     97a    98    100    102    1535  
 Induction    -S9  +S9  -S9  +S9  -S9  +S9  -S9  +S9  -S9  +S9
 H2O  Mean  139  109  13  11  152  185  212  192 15   16
   sd 58.2   11.6  1.7  3.8  25.1  31.1  22.0  58.2  3.6  5.7
 DMSO  Mean  136  155  8  10  206  178  204  221  18  15
   sd  16.8  49.5  4.7 3.4  30.2  34.9  12.4  73.3  2.4  5.4
 Pos Contr  Mean  1001  1001  1001  1001  1001  1001  1001  1001  1001  1001
   sd  0  0  0  0  0  0  0 0  0  0 
  f(I)  7.36  6.46  125.1  100.1  6.59  5.62  4.91  4.53  66.73  66.73
 4998 µg/pl.  Mean  171  100  10  9 129   183  198  209  19  14
   sd  28  8 3 1   11  17  18  68  6  2 
   f(I)  1.23  0.92  0.77  0.82 0.85  0.99  0.93  1.09  1.27  0.88 
 1499 µg/pl.  Mean  156  146  12  9  170  160  198  178  15  18
   sd  17  29  3  3  19  30  32  54  4  3
   f(I)  1.12  1.36  0.92  0.82  1.12  0.86  0.93  0.93  1.00  1.13
 500 µg/pl.  Mean  139  133  16  8  160  152  157  176  13  15
   sd  43  10  4  2  25  59  31  51  2  4
   f(I)  1.00 1.22   1.23  0.73  1.05  0.82  0.74  0.92  0.87  0.94
 150 µg/pl.  Mean  134  113  10  9  152  178  209  168  15  12
   sd  41  7  4  2  17  37  50  45  4  4
   f(I)  0.96  1.04  0.77  0.82  1.00  0.96  0.99  0.88  1.00  0.75
 50 µg/pl.  Mean  135  145  10  6  145  127  218  200  17  20
   sd  42  34  4  2  11  26  18  54  2  5
   f(I) 0.97  1.33  0.77   0.55  0.95  0.69  1.03  1.04  1.13  1.25

In this table ">1000" is represented by "1001"

Mean Revertants Second Experiment:

Strain   97a    98 100  102    1535  
 Induction  -S9  +S9  -S9  +S9  -S9  +S9  -S9  +S9  -S9  +S9
 H2O  Mean  99  118  5  12  160  151  156  137  15  13
   sd  54.9  13.6  1.7  3.9  23.5  20.1  14.0  25.0  1.8  4.9
 DMSO Mean   152  115  7  12  142  133  167  164  8  11
   sd  9.6  6.1  0.8  3.4  17.0  1.9  8.6  31.0  2.1  2.2
 Pos.Contr.  Mean  1001  1001  1001  1001  1001  1001  1001  1001  1001  1001
   sd  0  0  0  0  0  0  0  0  0  0
   f(I)  6.59  8.70  143.0  83.42  6.26  7.53  5.99  6.10  66.73  91.00
 4998 µg/pl. Mean   126  115  8  11  112  187  141  156  10  15
   sd  35  45  4 5  10  46  15    27  3  5
   f(I)  1.27  0.97  1.60  0.92 0.70   1.24  0.90  1.14  0.67  1.15
 2499 µg/pl.  Mean  123  142  8  7  150  130  185  143  12  9
   sd  39  24  4  6  14  47  13  46  6  3
   f(I)  1.24  1.20  1.60  0.58  0.94  0.86  1.19  1.04  0.80  0.69
 1250 µg/pl.  Mean  145  149  10  9  164  157  204  182  15  12
   sd  10  10  5  1  5  16  9  33  5  2
  f(I)   1.46  1.26 2.00  0.75  1.03  1.04  1.31  1.33   1.00  0.92

In this table "> 1000" is represented by "1001"

Conclusions:
Interpretation of results: negative

CC10 zirconium oxide is considered as "not mutagenic under the conditions of the test."
Endpoint:
genetic toxicity in vitro, other
Remarks:
in vitro gene mutation in bacteria, in vitro cytogenicity and gene mutation in mammalian cells
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
Read across based on studies performed with zirconium dioxide (in vitro gene mutation in bacteria, in vitro gene mutation in mammalian cells, in vitro cytogenicity in mammalian cells) and magnesium oxide (in vitro gene mutation in bacteria). The read across justification document is attached in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Reason / purpose for cross-reference:
read-across source
Key result
Remarks on result:
other: Magnesium zirconium oxide is concluded not to be genotoxic.
Remarks:
Conclusion based on the results of a series of read across studies: Ames tests with zirconium dioxide (LAUS, 2008) and magnesium hydroxide (Verspeek-Rip, 2010b), an in vitro cytogenicity study in mammalian cells with zirconium dioxide (NOTOX, 2010a) and an in vitro gene mutation study in mammalian cells with zirconium dioxide (NOTOX, 2010b).
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

1. Information on zirconium dioxide

Bacterial reverse mutation test:

LAUS (2008) performed a bacterial reverse mutation study according to OECD guideline 471 and EU method B13/14. Salmonella typhimurium strains TA97a, TA98, TA100, TA102 and TA1535 were exposed to 50 to 4998 µg/plate with and without metabolic activation in two independent experiments. Vehicle and positive controls were valid. Zirconium dioxide did not induce mutation with and without metabolic activation and no cytotoxicity was observed.

In vitro cytogenicity in mammalian cells:

NOTOX (2010a) performed a chromosome aberration test according to OECD guideline 473. Cultured peripheral human lymphocytes were exposed for 3 hours to 10, 33 and 100 µg zirconium dioxide/mL culture medium with and without S9-mix (dose range finding test/first cytogenetic assay); at 24 and 48 h continuous exposure time blood cultures were treated with 1, 3, 10, 33, 100, 333 and 1000 µg zirconium dioxide/mL culture medium without S9-mix. A second cytogenicity test was performed as follows: without S9-mix: 10, 33 and 100 µg/mL culture medium (24 and 48 h exposure time, 24 h and 48 h fixation time); with S9-mix: 10, 33 and 100 µg/mL culture medium (3 h exposure time, 48 h fixation time). Vehicle and positive control substances were tested simultaneously and considered valid. Zirconium dioxide tested negative with and without metabolic activation. No cytotoxicity was observed.

In vitro gene mutation in mammalian cells:

NOTOX B.V. (2010b) performed a mouse lymphoma test according to OECD guideline 476. Mouse lymphoma L5178Y cells were exposed to 0.03, 0.1, 1, 3, 10, 33 and 100 µg/mL zirconium dioxide with and without metabolic activation. In a first experiment, cell cultures were exposed for 3 hours to zirconium dioxide in exposure medium in the absence and presence of S9-mix. In a second experiment, cell cultures were exposed to zirconium dioxide in exposure medium for 24 hours in the absence of S9-mix and for 3 hours in the presence of S9-mix. Zirconium dioxide tested negative in both experiments with and without metabolic activation. No cytotoxicity was observed and positive and vehicle controls were considered valid.

2. Information on magnesium oxide

Bacterial reverse mutation test:

Verspeek-Rip (2010b) performed a bacterial reverse mutation test with magnesium hydroxide according to OECD guideline 471. This test is considered relevant for magnesium oxide because magnesium oxide is transformed to magnesium hydroxide when in contact with moisture, such as bodily fluids.

In this study, magnesium hydroxide was tested in the Salmonella typhimurium reverse mutation assay with four histidine-requiring strains of Salmonella typhimurium (TA1535, TA1537, TA98 and TA100) and in the Escherichia coli reverse mutation assay with a tryptophan-requiring strain of Escherichia coli (WP2uvrA). The test was performed in two independent experiments in the presence and absence of S9-mix (rat liver S9-mix induced by a combination of phenobarbital and β-naphthoflavone). The substance tested negative in all strains both in the absence and presence of metabolic activation, under the conditions of the test.

3. Conclusion on magnesium zirconium oxide

Based on the comparison of basic toxicological data (Annex VII endpoints), the read across assumption (i.e., addition of magnesium (oxide) to the crystal lattice of zirconium dioxide does not alter the unhazardous character of zirconium dioxide) was considered valid. For gene mutation in bacterial cells (Ames test), data for both zirconium dioxide and magnesium (hydr)oxide were added to a weight of evidence approach. Both compounds tested negative both in the absence and presence of metabolic activation, under the conditions of the test. The higher endpoints (in vitro gene mutation in mammalian cells and cytogenicity in mammalian cells) were then covered by data for zirconium dioxide alone. Based on the available data and the read across approach, magnesium zirconium oxide can safely be concluded not to be genotoxic.

Justification for classification or non-classification

1. Information on zirconium dioxide

Zirconium dioxide did not induce any mutation or chromosome aberration in three different in vitro studies and therefore, the substance should not be classified for genetic toxicity.

2. Information on magnesium oxide

An Ames study with magnesium hydroxide (considered representative for magnesium oxide) yielded negative results in the absence and presence of metabolic activation, under the conditions of the test. Based on the read across approach it was not considered necessary to add further data on genetic toxicity for the substance to this dossier. Magnesium hydroxide and magnesium oxide are however not classified for genetic toxicity.

3. Conclusion on magnesium zirconium oxide

Based on the conclusions for zirconium dioxide and magnesium (hydr)oxide, no classification for genetic toxicity is required for magnesium zirconium oxide either.