Registration Dossier

Diss Factsheets

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Gene mutation (Bacterial reverse mutation assay / Ames test): negative with and without activation in all strains tested (OECD TG 471) (Microbiological Associates (1995))


Cytogenicity in mammalian cells: negative without activation, considered to be positive structural, negative numerical with activation (OECD TG 473) (BioReliance (2007)). However the positive effects were observed only in the highest, overtly cytotoxic concentrations so the substance is considered to be negative for cytogenicity.

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro gene mutation study in bacteria
Remarks:
Type of genotoxicity: gene mutation
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:
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, TA 100 and E. coli WP2
Metabolic activation:
with and without
Metabolic activation system:
Aroclor 1254-induced rat liver S9 homogenate 
Test concentrations with justification for top dose:
100, 333, 1000, 3333, and 5000 µg/plate
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO

- Justification for choice of solvent/vehicle: the solvent was chosen based on solubility of the test article and compatibility with the target cells.
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
2-nitrofluorene
Remarks:
TA 98 (without activation)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
sodium azide
Remarks:
TA 100, TA 1535 (without activation)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
9-aminoacridine
Remarks:
TA 1537 (without activation)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
methylmethanesulfonate
Remarks:
WP2, WP2uvrA (without activation)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 2-Aminoanthracene
Remarks:
All strains (with activation)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: Sterigmatocystin
Remarks:
All strains (with activation)
Details on test system and experimental conditions:
METHOD OF APPLICATION: in agar (plate incorporation); preincubation

DURATION

- Preincubation period: 60 minutes

- Expression time (cells in growth medium): 48 to 72 hours

NUMBER OF REPLICATIONS: 2 plates per test concentration

DETERMINATION OF CYTOTOXICITY

- Method: relative total growth; background lawn assessment
Evaluation criteria:
The test article is evaluated as positive when it causes a dose-related increase in mean revertants per plate of at least one tester strain with a minimum of two increasing concentrations of test article.
Statistics:
Positive controls and tester strains with revertant counts greater than 100 were counted with a colony counter (Mini Count) and those less than 100 were counted manually.
Key result
Species / strain:
S. typhimurium TA 98
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Remarks:
> 5000 µg/plate
Vehicle controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium 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
Remarks:
> 5000 µg/plate
Vehicle controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Remarks:
> 5000 µg/plate
Vehicle controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1537
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Remarks:
> 5000 µg/plate
Vehicle controls validity:
valid
Positive controls validity:
valid
Key result
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
Remarks:
> 5000 µg/plate
Vehicle controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
E. coli WP2
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
Positive controls validity:
valid
Additional information on results:
TEST-SPECIFIC CONFOUNDING FACTORS
- Effects of pH: none recorded
- Effects of osmolality: none recorded
- Evaporation from medium: not reported
- Precipitation: Slight precipitation at higher concentrations did not affect assay
- Other confounding effect: In first two tests, a variation in the precipitation pattern was observed, so the tests were repeated. The findings from the initial two experiments are not recorded.

RANGE-FINDING/SCREENING STUDIES:
No toxicity observed

COMPARISON WITH HISTORICAL CONTROL DATA:
The results of the controls lie within the range of the historical control data.


ADDITIONAL INFORMATION ON CYTOTOXICITY: None
Remarks on result:
other: all strains/cell types tested

 Table 1 Preliminary toxicity test

 

TA 100

WP2 uvrA (pKM101)

Concentration (µg/Plate)

Plate 1

+ MA

Plate 2

- MA

Cytotoxic (Yes/No)

Plate 1

+ MA

Plate 2

- MA

Cytotoxic (Yes/No)

0

199

174

no

250

208

no

6.7

180

173

no

234

187

no

10

165

157

no

241

210

no

33

174

163

no

200

198

no

67

179

197

no

228

185

no

100

196

152

no

195

217

no

333

177

170

no

186

184

no

667

175

175

no SP

230

214

no SP

1000

169

156

no SP

138

168

no SP

3333

199

174

no SP

221

169

no SP

5000

174

158

no SP

247

180

no SP

SP Slight precipitate

 

Table 2: Experiment 1 Plate incorporation assay [Number of revertants per plate (mean of 3 plates)]

 

TA98

TA100

TA1535

Conc.
(
µg/plate)

-MA

+ MA

Cytotoxic
(yes/no)

-

 MA

+ MA

Cytotoxic
(yes/no)

-

MA

+ MA

Cytotoxic
(yes/no)

0*

13

17

no

95

144

no

10

11

no

100

13

17

no

89

127

no

9

11

no

333

13

18

no

86

135

no

8

11

no

1000

14

16

no

85

116

no

9

11

no

3333

17

21

no

97

116

no

6

14

no

5000

13

21

no

95

111

no

7

13

no

Positive Control

1304

1050

-

581

997

-

497

124

-

*solvent control with DMSO

 

Table 2: Experiment 1 Plate incorporation assay [Number of revertants per plate (mean of 3 plates)]

 

TA1537

WP2 uvrA (pKM101)

WP2 (pKM101)

Conc.
(
µg/plate)

-MA

+ MA

Cytotoxic
(yes/no)

-

 MA

+ MA

Cytotoxic
(yes/no)

-

MA

+ MA

Cytotoxic
(yes/no)

0*

4

6

no

226

263

no

65

64

no

100

4

10

no

236

295

no

54

64

no

333

3

5

no

239

258

no

87

60

no

1000

6

8

no

210

294

no

62

53

no

3333

5

8

no

213

273

no

67

64

no

5000

5

6

no

197

247

no

67

61

no

Positive Control

215

130

-

1554

1262

-

1476

499

-

 

 *solvent control with DMSO

 

Table 3: Experiment 2 Pre incubation assay [Number of revertants per plate (mean of 3 plates)]

 

TA98

TA100

TA1535

Conc.
(
µg/plate)

— MA

+ MA

Cytotoxic
(yes/no)

 MA

+ MA

Cytotoxic
(yes/no)

MA

+ MA

Cytotoxic
(yes/no)

0*

15

24

no

102

129

no

11

10

no

50

26

24

no

112

122

no

10

11

no

160

21

20

no

105

116

no

11

9

no

500

24

14

no

101

120

no

12

10

no

1600

23

17

no

110

128

no

9

12

no

5000

19

18

no

100

123

no

10

11

no

Positive Control

764

909

-

527

902

-

433

117

-

*solvent control with DMSO

 

Table 3: Experiment 2 Pre incubation assay [Number of revertants per plate (mean of 3 plates)]

 

TA1537

WP2 uvrA (pKM101)

WP2 (pKM101)

Conc.
(
µg/plate)

-MA

+ MA

Cytotoxic
(yes/no)

-

 MA

+ MA

Cytotoxic
(yes/no)

-

MA

+ MA

Cytotoxic
(yes/no)

0*

5

7

no

204

334

no

23

21

no

100

5

5

no

274

278

no

25

21

no

333

5

5

no

173

316

no

26

25

no

1000

5

6

no

208

296

no

26

22

no

3333

5

4

no

206

285

no

31

28

no

5000

5

6

no

214

283

no

28

24

no

Positive Control

250

119

-

2225

1304

-

358

1222

-

 

*solvent control with DMSO

 

Conclusions:
Trimethoxysilane has been tested according to OECD Test Guideline 471 and in compliance with GLP. No increase in the number of revertants was observed with or without metabolic activation in either the initial or the repeat assay using Salmonella typhimurium strains and E. coli WP2 uvrA, using the preincubation method. Appropriate solvent and positive controls were included and gave expected results. It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of this study.
Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Remarks:
Type of genotoxicity: chromos ome aberration
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2006-08-16 to 2006-09-17
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)
GLP compliance:
yes
Type of assay:
in vitro mammalian chromosome aberration test
Species / strain / cell type:
Chinese hamster Ovary (CHO)
Metabolic activation:
with and without
Metabolic activation system:
Aroclor induced rat liver S9
Test concentrations with justification for top dose:
152.5, 305, 610, 1220 µg/ml

In the preliminary toxicity assay, the maximum dose tested was 1220 µg/ml (10 mM). The test article was soluble in DMSO and in the treatment medium at all dose levels tested at the beginning of the treatment period. At the conclusion of the treatment period, visible precipitate was observed in treatment medium at 1220 µg/ml and dose levels = 366 µg/ml were soluble in treatment medium.

Substantial toxicity (at least 50% cell growth inhibition relative to the solvent control) was observed at 1220 µg/ml in both the non-activated and S9-activated 4-hour exposure groups. Substantial toxicity was not observed at any dose level in the non-activated 20-hour exposure group. Based on these findings, the doses chosen for the chromosome aberration assay ranged from 152.5 to 1220 µg/ml for all three exposure groups.
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO

- Justification for choice of solvent/vehicle: solubility of the test article and compatibility with target cells.
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
mitomycin C
Remarks:
(without activation)
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
cyclophosphamide
Remarks:
(with activation)
Details on test system and experimental conditions:
METHOD OF APPLICATION: in medium

DURATION

- Preincubation period: 16 - 24 hours

- Exposure duration: 4 - 20 hours (-MA), 4 hours (+MA)

NUMBER OF REPLICATIONS: 2 flasks per concentration

DETERMINATION OF CYTOTOXICITY

- Method: Cell growth inhibition relative to the solvent control

Evaluation criteria:
Toxicity based on cell growth inhibition relative to solvent control.

The number and types of aberrations found, % aberrant cells in the total population of cells examined, and mean aberrations per cell were calculated and reported for each treatment group.

The test article was considered to induce a positive response when the percentage of cells with aberrations is increased in a dose-responsive manner with one or more concentrations being statistically significant (p=0.05).
Statistics:
Fisher's exact test was used to compare pairwise the percent aberrant cells of each treatment group with that of the solvent control. In the event of a positive Fisher's Exact test at any test article dose level, the Cochran-Armitage test was used to measure dose-responsiveness.
Key result
Species / strain:
Chinese hamster Ovary (CHO)
Metabolic activation:
with
Genotoxicity:
other: considered positive structural, negative numerical
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
1220 µg/ml (4 hour group)
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
Chinese hamster Ovary (CHO)
Metabolic activation:
without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
1220 µg/ml (4 hour group)
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid

Table 1: Preliminary toxicity test using Trimethoxysilane in CHO cells with and without S9 metabolic activation (4 hour treatment / 16 hour recovery) 

 

 

- MA

+ MA

- MA

 

4 hour treatment / 16 hour recovery

20 hour continuous treatment)

Treatment

µg/ml

Cell Viability (%)

Cell Growth Index (%) *

Cell Growth Inhibition (%) **

Cell Viability

(%)

Cell Growth Index (%) *

Cell Growth Inhibition (%) **

Cell Viability (%)

Cell Growth Index (%) *

Cell Growth Inhibition (%) **

DMSO

98

100

-

98

100

-

100

100

-

0.122

99

95

5

100

89

11

99

86

14

0.366

99

79

21

100

96

4

99

92

8

1.22

100

82

18

97

97

3

100

85

15

3.66

97

76

24

99

80

20

97

87

13

12.2

99

78

22

97

81

19

95

86

14

36.6

98

67

33

98

86

14

96

99

1

122

98

63

37

100

98

2

97

94

6

366

99

68

32

99

78

22

98

87

13

1220

93

41

59

95

42

58

91

67

33

* Cell Growth Index = (cells per flask treated group/cells per flask control group), expressed as a percentage

** Cell Growth Inhibition = 100 % - % cell growth index; not calculated for negative controls 

Table 2: Cytogenetic analysis of CHO cells in the absence of metabolic activation (4 hour treatment, 16 hour recovery period)

 

 

Control*

152.5 µg/ml

305 µg/ml

610 µg/ml

Positive control

Flask

A

B

A

B

A

B

A

B

A

B

Cytotoxicity

no

no

no

no

no

no

yes

yes

no

no

Chromatid aberrations***

Breaks

0

0

0

0

0

0

1

0

10

7

Interchanges

0

0

0

0

0

0

0

0

0

1

Chromosome aberrations***

Gaps**

0

0

1

0

0

0

0

0

1

0

Breaks

0

0

0

0

0

0

0

0

0

0

Dicentric

0

0

0

0

0

0

0

0

0

0

Rings

0

0

0

0

0

0

0

0

0

0

% aberrant cells

Numerical

2

3

5

5

4

5

3

3

1

2

Structural

0

0

0

0

0

0

1

0

28

24

Mitotic index

 

11.0

11.4

10.8

10.4

10.0

10.4

9.6

8.8

7.4

6.8

* Solvent control with DMSO

** Total gaps

*** Total number of aberrations

Mitotic Index = number of mitotic figures x 100/500 cells counted

% Aberrant Cells: numerical cells include polyploid and endo reduplicated cells; structural cells exclude cells with only gaps

 

Table 3: Cytogenetic analysis of CHO cells in the presence of metabolic activation (4 hour treatment, 16 hour recovery period)

 

 

Control*

152.5 µg/ml

305 µg/ml

1220 µg/ml

Positive control

Flask

A

B

A

B

A

B

A

B

A

B

Cytotoxicity

no

no

no

no

no

no

yes

yes

yes

yes

Chromatid aberrations***

Breaks

0

0

0

1

0

2

1

8

2

7

Interchanges

0

0

1

1

3

1

7

4

8

6

Chromosome aberrations***

Gaps**

1

0

1

0

2

0

2

3

0

1

Breaks

0

0

0

0

0

0

0

0

0

0

Dicentric

0

1

0

0

0

0

1

1

0

0

Rings

0

0

0

0

0

0

0

0

2

1

% aberrant cells

Numerical

5

4

5

5

5

4

3

4

5

4

Structural

0

1

1

2

3

3

8

9

16

18

Mitotic index

 

11.6

11.6

11.2

11.4

10.6

11.2

5.4

6.4

4.0

3.8

* Solvent control with DMSO

** Total gaps

*** Total number of aberrations

Mitotic Index = number of mitotic figures x 100/500 cells counted

% Aberrant Cells: numerical cells include polyploid and endo reduplicated cells; structural cells exclude cells with only gaps

 

Table 4: Cytogenetic analysis of CHO cells in the absence of metabolic activation (20 hour continuous treatment)

 

 

Control*

152.5 µg/ml

305 µg/ml

610 µg/ml

Positive control

Flask

A

B

A

B

A

B

A

B

A

B

Cytotoxicity

no

no

no

no

no

no

yes

yes

no

no

Chromatid aberrations***

Breaks

0

0

0

0

0

1

0

0

4

3

Interchanges

0

0

0

0

0

0

0

0

2

3

Chromosome aberrations***

Gaps**

0

0

0

0

0

0

0

1

1

0

Breaks

0

0

0

0

0

0

0

0

0

0

Dicentric

0

0

0

0

0

0

0

0

0

0

Rings

0

0

0

0

0

0

0

0

0

0

% aberrant cells

 

 

Numerical

3

4

4

4

4

3

4

4

4

3

Structural

0

0

0

0

0

1

0

0

24

20

Mitotic index

 

10.4

10.0

10.2

10.4

9.4

10.0

5.2

4.8

6.6

6.0

* Solvent control with DMSO

** Total gaps

*** Total number of aberrations

Mitotic Index = number of mitotic figures x 100/500 cells counted

% Aberrant Cells: numerical cells include polyploid and endo reduplicated cells; structural cells exclude cells with only gaps

 

 

Conclusions:
In a reliable study conducted in accordance with OECD Test Guideline 473 and in compliance with GLP, trimethoxysilane was concluded to be positive for the induction of structural and negative for the induction of numerical chromosome aberrations in CHO cells in the S9-activated test system at the highest dose tested. However these effects were observed only in the highest, overtly cytotoxic concentration, so the substance is considered to be negative for cytogenicity. Appropriate solvent and positive controls were included and gave expected results.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

Micronucleus assay inhalation study in rat: negative (similar to OECD TG 474) (Dow Corning Corporation (1982))

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:
1982-04-21 to 1982-05-14
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The study was conducted according to an appropriate OECD test guideline with minor deviations. It was conducted in compliance with GLP. The deviations are that only 1000 cells were scored compared with 2000 in current guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
Deviations:
yes
Remarks:
1000 cells scored
Principles of method if other than guideline:
Micronucleus test in vivo: Matter and Schmid, 1971, Mut. Res. 12: 417-425.
GLP compliance:
yes
Type of assay:
micronucleus assay
Species:
rat
Strain:
Sprague-Dawley
Sex:
female
Details on test animals or test system and environmental conditions:
TEST ANIMALS

- Source: Spartan Research Laboratories, Inc. Harlet, MI

- Weight at study initiation: 100 to 175 grams

- Housing: Animals housed individually

- Diet (e.g. ad libitum): PURINA Rodent Laboratory Chow (ad libitum)

- Water (e.g. ad libitum): ad libitum
Route of administration:
inhalation
Vehicle:
- Vehicle(s)/solvent(s) used: air

- Concentration of test material in vehicle: 100 ppm
Details on exposure:
TYPE OF INHALATION EXPOSURE: nose only

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION

- Exposure apparatus: specially constructed glass chamber

- System of generating particulates/aerosols: vapours were generated by bubbling clean, dry air through the liquid test material
Duration of treatment / exposure:
4 hour(s)
Frequency of treatment:
Single 4 hour exposure
Post exposure period:
30 hours
Remarks:
Doses / Concentrations:
100 ppm
Basis:
nominal conc.
No. of animals per sex per dose:
5 animals per dose level
Control animals:
yes, concurrent no treatment
Positive control(s):
triethylenemelamine

- Route of administration: split-dose intraperitoneal injection (0 and 24 hours)

- Doses / concentrations: 0.5 mg/kg/dose
Tissues and cell types examined:
Animals were exposed to the test article by acute inhalation. They were sacrificed, the bone marrow is extracted and smear preparations made and stained. Polychromatic erythrocytes are scored for micronuclei under the microscope. Both positive and negative (solvent) controls are used in each experiment.
Details of tissue and slide preparation:
At sacrifice the adhering soft tissue and epiphyses of both tibiae were removed. The marrow was aspirated from the bone and transferred to centrifuge tubes containing 5 ml fetal calf serum (one tube for each animal). Following centrifugation to pellet the tissue, the supernatant was drawn off and portions of the pellet was spread on slides and air-dried. The slides were then stained in May-Gruenwald Solution and Giemsa. A thousand polychromatic erythrocytes (PCEs) per animal were scored. The frequency of micronucleated was expressed as percent micronucleated cells based on the total PCEs present in the scored optic field.
Evaluation criteria:
In the normal animal, the normocytes/PCE's is approximately 2. If an agent inhibits the proliferation of erythroblasts the proportion of PCE's is generally reduced. If the agent promotes chromosome breakage or acts as a spindle poison, generally the proportion of red normocytes increases.
Statistics:
Mean normocyte and polychromatic erythrocytes calculated as well as ratio of normocytes to PCE's
Key result
Sex:
female
Genotoxicity:
negative
Toxicity:
yes
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
RESULTS OF RANGE-FINDING STUDY

- Dose range: 100 ppm

- Clinical signs of toxicity in test animals: To ensure that the Micronucleus Assay was performed on animals exposed to a lethal concentration of the test material (Group A), a second group of animals (Group B) was simultaneously exposed to the chemical via inhalation as a positive control for lethality. The data demonstrates that both groups (A&B) was exposed to a lethal concentration of the test material. All five animals in Group B experienced weight loss and died within the 14 day observation period. At autopsy all five animals showed extensive lung damage with hemorrhage and atelectasis. Animals exposed via inhalation to the test material all showed slight to moderate evidence of lung damage in the form of petechial hemorrhage and focal atelectasis. Some evidence of kidney congestion was noted in several animals. No abnormal pathology was evident in either the positive control (C) or negative control (D) groups.

- Evidence of cytotoxicity in tissue analyzed: The ratio of of normocytes to PCE's obtained with both the test material treatment (Group A = 10.64) and the negative control (Group D = 10.28) closely approximate the normal expected ratio and were fairly consistent. The mean normocyte count from the positive control group was elevated (Group C = 19.4) indicating that the animals responded to a known clastogen (chromosome breaking agent). This same trend verified by the increase in percentage of micronucleated PCEs in the positive control group.

- Harvest times: Group A (Treatment group): 30 hours after exposure. Group B (Toxicity Control): 14 days. Group C (Positive Control): 30 hours. Group D (Negative Control): 30 hours.

- High dose with and without activation: 100 ppm

RESULTS OF DEFINITIVE STUDY

- Induction of micronuclei (for Micronucleus assay): Within normal range for all groups

- Ratio of PCE/NCE (for Micronucleus assay): Within normal range for all groups

- Statistical evaluation: Comparison of the study groups by Student T-test using a SAS computer program confirms there is no difference between the mean PCE micronucleus count for study groups A and D (test article and negative control) (<.0001) while the positive control is definitely positive (p>0.5) compared to the former groups.

The following table indicates that the animals responded to the positive control substance.

Both Normocytes/PCE **  ratio and % of micronucleated PCEs were significantly increased in the positive control group when compared to test material-treated group.

Table 3 : Mean Results of in vivo micronucleus test with mouse bone marrow

 

Test Group

(A)

Positive Control (C)

Negative Control (D)

Number of cells evaluated

1000

1000

1000

Sampling time (h)

30h

30h

30h

Number of erythrocytes

Normocytes / Field

10.64

19.4

10.28

PCE / Field

4.36

4.56

4.36

Micronuclei / 1000 PCE

6.8

39.2

5.6

Ratio of erythrocytes

Normochromatic / polychromatic

2.52

4.38

2.39

% Micronucleated PCE

0.68

3.92

0.56

 

Conclusions:
In a reliable study conducted according to a protocol similar to the OECD Test Guideline 474 with minor deviations, trimethoxysilane did not induce chromosome breakage or act as a spindle poison in the rodent micronucleus assay even when animals were exposed to lethal concentrations. There is no evidence from this study that the mechanism of kill at toxic levels of exposure involves genotoxicity. The test substance is non-mutagenic in Sprague-Dawley rats under the conditions of this mammalian micronucleus assay.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

In vitro studies are available for trimethoxysilane for bacterial mutagenicity and cytogenicity in mammalian cells. The results from bacterial mutation tests are in agreement, with both available tests giving negative results. There was evidence for clastogenicity (causing chromosomal aberrations) in the presence of metabolic activation in vitro. However this evidence was observed only in the highest, overtly cytotoxic concentrations, so the substance is considered to be negative for cytogenicity.

In addition, an in vivo study concluded that the in vitro result does not reflect an ability to cause chromosome aberrations in vivo. In view of the availability of an in vivo study, it is not considered necessary to test for mutagenicity in mammalian cells in vitro.

Trimethoxysilane has been tested according to OECD Test Guideline 471 and in compliance with GLP. No increase in the number of revertants was observed with or without metabolic activation in either the initial or the repeat assay using Salmonella typhimurium strains and E. coli WP2 uvrA using the preincubation method.

It is concluded that the test substance is negative for mutagenicity to bacteria under the conditions of this study (Microbiological Associates 1995).

This result is supported by a summary of a reliable study conducted according to OECD Test Guideline 471 and in compliance with GLP. The test substance trimethoxysilane did not demonstrate genetic activity in any of the strains used in this study, both with and without metabolic activation. The results indicate that the test substance was not considered mutagenic under the test conditions of OECD 471. (Dow Corning Corporation 1987).

The potential for induction of damage to chromosomes in mammalian cells was investigated by testing trimethoxysilane in a study conducted in accordance with OECD Test Guideline 473 and in compliance with GLP (BioReliance 2007). Trimethoxysilane was concluded to be positive for the induction of  structural and negative for the induction of numerical chromosome aberrations in CHO cells in the S9 activated test system at the highest dose tested. However the positive effects were observed only in the highest, overtly cytotoxic concentrations, so the substance is considered to be negative for cytogenicity.

Trimethoxysilane has been tested in an in vivo mammalian micronucleus study conducted according to a protocol similar to the OECD Test Guideline 474 (with minor deviations). The test substance did not induce chromosome breakage or act as a spindle poison in the rodent micronucleus assay even when animals were exposed to lethal concentrations. There was no evidence from this study that the mechanism of kill at toxic levels of exposure involves genotoxicity.

Therefore it is concluded that the test substance is non-mutagenic in Sprague-Dawley rats under the conditions of this mammalian micronucleus assay.

Justification for classification or non-classification

The available information for the substance indicates that trimethoxysilane (CAS 2487-90-3) does not induce mutations in bacterial cells. The substance does cause evidence of chromosomal aberrations in vitro in the presence of metabolic activation. However these effects were observed only at the highest, overtly cytotoxic concentrations, so the substance is considered to be negative for cytogenicity. In addition, clastogenic effects have not been observed in an in vivo study, so it is concluded that trimethoxysilane does not require classification as a germ cell mutagem according to Regulation (EC) No. 1272/2008.