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Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

There is no in vitro genetic toxicity data available for 2,3-Dimethylbutane. However, data is available for structural analogue, commercial hexane. This data is read across to 2,3-Dimethylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

 

The read across genetic toxicity tests listed below had negative results for 2,3-Dimethylbutane.

 

Genetic Toxicity in vitro – Bacterial reverse mutation assay (OECD 471)

Genetic Toxicity in vitro – Mammalian Chromosome Aberration Test (OECD TG 473)

Genetic Toxicity in vitro – Mammalian Cell Gene Mutation Test (OECD TG 476)

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1989-05-19 to 1989-07-06
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: This study is classified as reliable without restrictions because it is well documented and follows OECD Guideline 471.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
yes
Remarks:
The method was modified to use the dessicator methodology in order to test the mutagenicity of the vapor phase of the test substance.
GLP compliance:
yes (incl. QA statement)
Type of assay:
bacterial reverse mutation assay
Species / strain / cell type:
S. typhimurium, other: TA 1535, TA 1537, TA 1538, TA 98, TA 100
Metabolic activation:
with and without
Metabolic activation system:
S9 from aroclor induced rat liver
Test concentrations with justification for top dose:
0, 600, 1000, 3000, 6000, 9000 ppm
Untreated negative controls:
yes
Negative solvent / vehicle controls:
other: no solvent used
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 2-aminoanthracene, 2-nitrofluorene, sodium azide, 9-aminoacridine, 1,1-dichloroethene
Details on test system and experimental conditions:
METHOD OF APPLICATION: Prepared plates were placed uncovered and inverted in 9l dessicators. An appropriate amount of test substance was placed in a glass petri dish was suspended at the bottom of the dessicator. A magnetic stirring bar was placed at the bottom of the dessicator, and served as a fan to ensure even distribution of the vapor.


DURATION
- Preincubation period: 48 hrs
- Exposure duration: 7-8 hrs at 37 degree C
- Expression time (cells in growth medium): There was an additional incubation time of 40 hrs after exposure.

NUMBER OF REPLICATIONS: 3


Evaluation criteria:
To be considered positive for mutation, at least a doubling of mean revertants per plate in at least one tester strain must be seen. This increase must be dose-related.
Statistics:
Mean number of revertant per plate and the standard deviation was calculated.
Key result
Species / strain:
S. typhimurium TA 1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
not examined
Untreated negative 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
Vehicle controls validity:
not examined
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1538
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
not examined
Untreated negative controls validity:
valid
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 98
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
not examined
Untreated negative 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
Vehicle controls validity:
not examined
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
No positive responses were observed in any of the tester strains. The positive control substance, 2-aminoanthracene, did not produce any mutations in strain TA 1538 in one experiment in the presence of S9. As revertants were seen in the test of TA 1538 without S9, and revertants were seen in other strains exposed to positive controls with S9, the lack of revertants was most likely due to a technical error and the study is still considered valid.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.

Average Revertants per Plate (SD) - Experiment B1

Dose (ppm)

TA 98

TA 100

TA 1535

TA 1537

TA 1538

Without S9

0.0

17 ± 1

105 ± 12

11 ± 1

7 ± 1

8

600

20 ± 5

113 ±  9

13 ± 4

6 ± 1

6

1000

16 ± 3

121 ± 8

14 ± 2

7 ± 1

6

3000

18 ± 4

112 ± 13

17 ± 3

5 ± 4

4

6000

24 ± 4

117 ± 14

12 ± 4

6 ± 4

8

9000

17 ± 3

112 ± 7

14 ± 5

9 ± 2

5

Positive control

227 ± 8

422 ± 44

349 ± 36

481 ± 135

452

With S9

0.0

24 ± 5

119 ± 10

17 ± 1

7 ± 0

12

600

30 ± 10

137 ± 12

23 ± 4

9 ± 4

15

1000

23 ± 5

126 ± 3

14 ± 2

11 ± 5

13

3000

22 ± 1

120 ± 19

16 ± 2

9 ± 2

9

6000

24 ± 2

103 ± 11

14 ± 4

7 ± 2

11

9000

30 ± 6

120 ± 3

17 ± 1

8 ± 2

14

Positive control

3142 ± 139

3902 ± 68

189±  22

351 ± 26

--

Positive vapor control

372 ± 52

Average Revertants per Plate (SD) - Experiment B2

Dose (ppm)

TA 98

TA 100

TA 1535

TA 1537

TA 1538

Without S9

0.0

12 ± 2

107 ± 11

9 ± 5

5 ± 1

19

600

20 ± 1

103 ±  9

8 ± 4

7 ± 3

19

1000

14 ± 4

110 ± 6

12 ± 5

7 ± 2

19

3000

14 ± 1

124 ± 14

12 ± 2

7 ± 2

19

6000

22 ± 6

125 ± 14

15 ± 1

5 ± 2

16

9000

15 ± 6

114 ± 5

13 ± 3

5 ± 3

13

Positive control

444 ± 86

991 ± 67

758 ± 19

162 ± 51

754

With S9

0.0

21 ± 4

132 ± 16

17 ± 4

7 ± 3

26

600

25 ± 7

133 ± 8

18 ± 2

6 ± 1

25

1000

22 ± 2

155 ± 4

15 ± 7

8 ± 3

25

3000

20 ± 1

123 ± 23

16 ± 7

7 ± 3

24

6000

21 ± 4

151 ± 14

15 ± 1

6 ± 2

30

9000

25 ± 4

161 ± 8

11 ± 4

6 ± 1

27

Positive control

2187 ± 166

2229 ± 223

166 ±  32

230 ± 24

2195

Positive vapor control

394 ± 50

Conclusions:
Interpretation of results: negative

The test substance is not mutagenic.
Executive summary:

This study examined the mutagenicity of vapors of the test substance commercial hexane. Plates of S. typhimurium were exposed for 7 -8 hrs to test atmospheres of 0, 600, 1000, 3000, 6000, or 9000 ppm of test substance. 20,000 ppm of 1,1 -dichloroethene was used a vapor-phase positive control substance.

The test substance did not produce a positive response in any of the test strains. The test substance is not mutagenic.

Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1989-08-24 to 1990-02-05
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: This study is classified as reliable without restriction because it followed a protocol comparable to OECD Guideline 473.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
reference to same study
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)
GLP compliance:
yes (incl. QA statement)
Type of assay:
in vitro mammalian chromosome aberration test
Species / strain / cell type:
Chinese hamster Ovary (CHO)
Additional strain / cell type characteristics:
other: CHO-K1 cells
Metabolic activation:
with and without
Metabolic activation system:
S9 from aroclor induced rat liver
Test concentrations with justification for top dose:
0.015, 0.034, 0.074, 0.123, 0.416 ul/ml without S9
0.014, 0.022, 0.056, 0.118, 0.251 ul/ml with S9
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: triethylenemelamine 0.5 ug/ml without S9, cyclophosphamide 50 ug/ml with S9
Details on test system and experimental conditions:
METHOD OF APPLICATION: 100 ul of dosing solutiong was added to the test medium


DURATION
- Preincubation period: 16-24 hrs at 37 degree C
- Exposure duration: 12 hrs without S9 at 37 degree in humidified air; 2 hrs with S9 at 37 degree in humidified air
- Expression time (cells in growth medium): For cells not treated with S9, two hours prior to cell harvest, treatment medium was removed and cells washed with PBS and refed with medium containing 0.1 ug/ml of Colcemid. For cells treated with S9, treatment medium was removed after exposure, cells were washed with PBS, refed, and returned to the incubator for 16 hrs. Colcemid was added at 0.1 ug/ml, and flasks incubated for two hrs.
- Fixation time (start of exposure up to fixation or harvest of cells): 14-20 hrs, collected by centrifugation



SELECTION AGENT (mutation assays):
SPINDLE INHIBITOR (cytogenetic assays):
STAIN (for cytogenetic assays): 5% Giemsa


NUMBER OF REPLICATIONS: 2


NUMBER OF CELLS EVALUATED: 100 per concentration


DETERMINATION OF CYTOTOXICITY
- Method: mitotic index and cell cycle delay


OTHER EXAMINATIONS:
Chromatid and isochromatid breaks, exchange figures, chromosome breaks, fragments, pulverized chromosomes, chromatid and isochromatid gaps


OTHER:
Evaluation criteria:
In order for the test to be valid, there must be no more than 6% cells with chromosome aberrations in the negative and solvent control groups. Positive control must be statistically increased over untreated controls (p<=0.05, Fisher's exact test). A positive result is percentage of cells with aberrations was statistically increased over untreated controls (p<=0.05, Fisher's exact test).
Statistics:
Fisher's exact test was used to determine statistical significance. Cochran-Armitage test was used to test dose-responsiveness.
Key result
Species / strain:
Chinese hamster Ovary (CHO)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
>= 0.074 ul/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
Toxicity was observed at concentrations of 0.074 µL/mL or greater. No significant increase in chromosome aberrations was seen in treatment groups.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.

Results of CHO Chromosome Aberration Assay

Dose (µl/ml)

Mitotic Index

Cells Scored

Aberrations per cell (mean ± SD)

% Cells with Aberrations

Without S9

Negative Control

5.7

100

0.010 ± 0.100

1

Solvent Control

4.9

100

0.010 ± 0.100

1

0.015

4.8

100

0.000 ± 0.000

0

0.034

4.5

100

0.010 ± 0.100

1

0.074

2.9

100

0.010 ± 0.100

1

0.123

0.2

8

0.000 ± 0.000

0

0.416

0.0

0

Positive Control

2.2

100

0.360 ± 1.124

21

With S9

Negative Control

5.3

100

0.010 ± 0.100

1

Solvent Control

5.6

100

0.010 ± 0.100

1

0.014

5.3

100

0.010 ± 0.100

1

0.022

5.9

100

0.010 ± 0.100

1

0.056

3.1

100

0.010 ± 0.100

1

0.118

0.2

2

0.000 ± 0.000

0

0.251

0.0

0

Positive Control

2.5

100

0.840 ± 1.819

40

Conclusions:
Interpretation of results: negative

The test substance is not clastogenic.
Executive summary:

This study examined the potential for commercial hexane to cause chromosome aberrations in Chinese Hamster Ovary (CHO) cells. CHO cells were exposed to concentrations of 0, 0.015, 0.034, 0.074, 0.123, and 0.416 µL/mL without metabolic activation and 0, 0.014, 0.022, 0.056, 0.118, and 0.251 µL/mL with metabolic activation. 0.5 µg/mL triethylenemelamine was used a positive control without metabolic activation and 50 µg/mL cyclophosphamide was used as a positive control with metabolic activation.

 

Negative and positive controls were valid. There was no significant increase in chromosome aberrations in any test group. The test substance was cytotoxic at concentrations of 0.074 µL/mL or greater. The test substance is not clastogenic.

Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1989-08-28 to 1990-04-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: This study is classified as reliable without restrictions because it is well documented and follows OECD Guideline 476.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)
GLP compliance:
yes (incl. QA statement)
Type of assay:
mammalian cell gene mutation assay
Species / strain / cell type:
Chinese hamster Ovary (CHO)
Details on mammalian cell type (if applicable):

- Periodically checked for Mycoplasma contamination: yes
Additional strain / cell type characteristics:
other: K1-BH4
Metabolic activation:
with and without
Metabolic activation system:
S9 from aroclor induced rat liver
Test concentrations with justification for top dose:
0, 0.132, 0.098, 0.063, 0.0362, 0.0122 ul/ml (analytical)
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: ethylmethanesulphonate 0.2 ul/ml without metabolic activation, benzo(a)pyrene 4 ug/ml with metabolic activation
Details on test system and experimental conditions:
METHOD OF APPLICATION: 7.5 ml of test substance was added to 17.5 ml of DMSO and vortexed for 2 min. The solution was allowed to separate, and the bottom DMSO/test substance layer and diluted further with DMSO. Appropriate amounts were then added to the test medium.


DURATION
- Preincubation period: 18-24 hrs at 37 degree C
- Exposure duration: 5 hrs at 37 degree C
- Expression time (cells in growth medium): 18-24 at 37 degree C

NUMBER OF REPLICATIONS: 2


DETERMINATION OF CYTOTOXICITY
Replicates from each treatment concentration were pooled and cultured in triplicate (100 cells/60 mm dish). After 7 days of incubation, colonies were fixed with methanol , stained with Giemsa, and counted. Determination was based on relative cloning efficiency.

Evaluation criteria:
mutant frequency > 20 mutants per 10^6 clonable cells, at least twice the mutant frequency of negative and solvent controls, mutant frequency above negative and solvent controls of at least 11 mutants per 10^6 clonable cells
Statistics:
Students t-test (p <= 0.05)
Key result
Species / strain:
Chinese hamster Ovary (CHO)
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
Additional information on results:
None of the mutant frequencies in the test groups were significantly elevated over negative and solvent controls. The test substance was cytotoxic at concentrations of 0.063 ul/ml or greater.
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.

CHO/HGPRT Mutation Assay

Dose (µl/ml)

Total Colonies

Cloning Efficiency

Total Mutant Colonies

Mutants/106 Clonable Cells

Without S9

Negative control

310

1.03

19

18.4

Solvent Control

329

1.10

6

5.5

0.132

284

0.95

0

5.3

0.098

260

0.87

0

 5.8

0.063

321

1.07

0

0.9

0.0362

289

0.96

5

5.2

0.0122

294

0.98

12

12.2

Positive Control

282

0.94

227

241.5

With S9

Negative control

320

1.07

0

0.9

Solvent Control

330

1.10

1

0.9

0.132

299

1.00

0

1.0

0.098

299

0.99

0

1.0

0.063

256

0.85

4

4.7

0.0362

317

1.06

13

12.3

0.0122

293

0.98

13

13.3

Positive Control

239

0.80

91

114.2

Conclusions:
Interpretation of results: negative

The test substance is not mutagenic.
Executive summary:

This study determined the mutagenicity of commercial hexane to Chinese hamster ovary (CHO) cells. CHO cells were exposed to concentrations of 0, 0.132, 0.098, 0.063, 0.0362, or 0.0122 µL/mL both with and without metabolic activation for 5 hrs. The cells were then analyzed for mutation frequency. A concurrent cytotoxicity assay was performed.

 

Results of the mutagenicity assay show that the test substance is not mutagenic both in the presence and absence of metabolic activation. However, the test substance was cytotoxic at concentrations of 0.063 µl/mL or greater.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

There is no in vivo genetic toxicity data available for 2,3-Dimethylbutane. However, data is available for structural analogue, commercial hexane. This data is read across to 2,3-Dimethylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

 

The read across genetic toxicity test listed below had negative results for 2,3-Dimethylbutane.

 

Genetic Toxicity in vivo – Mammalian Bone Marrow Chromosome Aberration Test (OECD TG 475)

Link to relevant study records
Reference
Endpoint:
in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1990
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: This study is classified as reliable without restriction because it closely followed OECD Guideline 475.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Reason / purpose for cross-reference:
reference to same study
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)
Deviations:
yes
Remarks:
In order to test substance as a vapor, animals were exposed via nose-only inhalation.
GLP compliance:
yes (incl. QA statement)
Type of assay:
other: cytogenetics assay
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Harlan Sprague Dawley, Inc., Frederick, MD
- Age at study initiation: 6-8 weeks
- Weight at study initiation: 228-266 g males, 153-188 g females
- Assigned to test groups randomly: assigned using body weight randomization program
- Housing: singly in plastic cages, identified by ear tags
- Diet (e.g. ad libitum): certified laboratory rodent chow, ad libitum
- Water (e.g. ad libitum): tap water ad libitum
- Acclimation period: 10 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 72 degree F
- Humidity (%): 40-70
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark

Route of administration:
inhalation: vapour
Details on exposure:
TYPE OF INHALATION EXPOSURE: nose only


GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 360 ml polycarbonate chamber
- Method of holding animals in test chamber: Polycarbonate tubes were used to restrain the animals. Only the nose of the animals protruded into the chambers. A soft sponge was used as a plunger to hold the animals in place.
- Source and rate of air: filtered outside air
- Method of conditioning air: A Gilson peristaltic pump was used to meter test liquid in sealed resevoirs to vaporization flasks immersed in 57 degree C water. Air was passed through the flasks, then through teflon tubing to the exposure chamber. A calibrated rotameter was used to dilute the air to the appropriate concentration.
- Temperature, humidity, pressure in air chamber: monitored every 30 min.
- Air flow rate: monitored every 30 min.


TEST ATMOSPHERE
- Brief description of analytical method used: GC
- Samples taken from breathing zone: yes
Duration of treatment / exposure:
6 hrs per day
Frequency of treatment:
5 days
Post exposure period:
1 or 19 hrs after end of exposure
Remarks:
Doses / Concentrations:
0, 900, 3000, 9000 ppm (0, 3168, 10560, 31680 mg/m3)
Basis:
nominal conc.
No. of animals per sex per dose:
5 male and 5 female per dose
Control animals:
yes, sham-exposed
Positive control(s):
triethylenemelamine
- Route of administration: intraperitoneal injection
- Doses / concentrations: 0.5 mg/kg
Tissues and cell types examined:
bone marrow
Details of tissue and slide preparation:
TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields):
Colchicine was administered two hours prior to sacrifice to arrest cell division at metaphase. Animals were sacrificed by carbon dioxide asphyxiation. Bone marrow cells were removed from the femur by aspiration into HBSS. Cells were mixed well and kept in an ice bath until all samples were collected. After centrifuging for 10 min, the supernatent was discarded, and the cells resuspended in 5 ml 0.075 M KCl at 37 degree C. After incubating for 10 min, cells were again centrifuged and resuspended in fixative. This was repeated with fresh fixative.

DETAILS OF SLIDE PREPARATION:
Cells were again centrifuged for 10 min, the supernantant decanted, and the cells resuspended in 1 ml of fixative. Two drops were placed on a cold wet glass slide, and allowed to air dry. Three slides were prepared per animal. Slides were stained with 4% Giemsa.

METHOD OF ANALYSIS:
50 metaphase cells containing approx. 40 centromeres were scored if possible.

OTHER:
Evaluation criteria:
In order for the test to be valid, there must be no more than 4% cells demonstrating aberrations in the negative control group. Positive control must be statistically increased over untreated controls (p<=0.05, Fisher's exact test). A positive result is a percentage of cells with aberrations which was statistically increased over untreated controls (p<=0.05, Fisher's exact test).
Statistics:
Fisher's exact test was used to determine statistical significance. Cochran-Armitage test was used to test dose-responsiveness.
Key result
Sex:
male/female
Genotoxicity:
negative
Toxicity:
no effects
Vehicle controls validity:
not applicable
Negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
There was a decrease in body weight observed after the last exposure. This reduction is typical for nose-only exposure, and is considered to be due to restraint. There was no statistically significant increase in aberrations in the exposure groups.

Chromosomal Damage in Rat Bone Marrow - Male         

Dose (ppm)

Time Evaluated (hrs)

Cells with Aberrations (%)

Mean Aberrations per Cell per Animal

0

6

0.0

0.000 ± 0.000

0

24

0.0

0.000 ± 0.000

876

6

0.4

0.004 ± 0.009

876

24

0.0

0.000 ± 0.000

3249

6

0.0

0.000 ± 0.000

3249

24

0.4

0.004 ± 0.009

8715

6

0.8

0.008 ± 0.018

8715

24

0.4

0.004 ± 0.009

Positive Control

6

14.4

0.696 ± 0.121

Chromosomal Damage in Rat Bone Marrow - Female

Dose (ppm)

Time Evaluated (hrs)

Cells with Aberrations (%)

Mean Aberrations per Cell per Animal

0

6

0.8

0.008 ± 0.011

0

24

0.0

0.000 ± 0.000

876

6

0.4

0.004 ± 0.009

876

24

0.4

0.004 ± 0.009

3249

6

0.4

0.004 ± 0.009

3249

24

0.0

0.000 ± 0.000

8715

6

0.4

0.004 ± 0.009

8715

24

0.4

0.004 ± 0.009

Positive Control

6

20.8

0.900 ± 0.477

Conclusions:
Interpretation of results: negative

The test substance is not mutagenic.
Executive summary:

This study determined the effect of inhalation exposure of commercial hexane on rat bone marrow. Groups of 5 male and 5 female rats were exposed to 0, 900, 3000, and 9000 ppm of test substance vapor for 6 hrs/day for 5 days. 0.5 mg/Kg triethylenemelamine was used as a positive control substance. Animals were sacrificed 3 or 21 hrs after exposure, and the bone marrow from their femurs examined for cell aberrations.

There was no statistically significant increase in cell aberrations in any treatment group. The test substance is not mutagenic.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

No genetic toxicity data is available for 2,3-Dimethylbutane. However, data is available for structural analogue commercial hexane. This data is read across to 2,3 -Dimethylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

 

In Vitro

 

In vitro gene mutation study in bacteria

 

Commercial hexane

An in vitro gene mutation study in bacteria evaluated the mutagenicity of vapors of commercial hexane (52% n-hexane). According to the study report (API, 1989a; Klimisch score =1) plates of S. typhimurium were exposed for seven to eight hours to test atmospheres of 0, 600, 1000, 3000, 6000, or 9000 ppm of test substance. The test substance did not produce a positive response in any of the test strains.

 

In vitro Chromosome Aberration in Mammalian Cells

 

Commercial hexane

In an in vitro chromosome aberration study, Chinese Hamster Ovary (CHO) cells were exposed to concentrations of commercial hexane (52% n-hexane) of 0, 0.015, 0.034, 0.074, 0.123, and 0.416 µL/mL without metabolic activation and 0, 0.014, 0.022, 0.056, 0.118, and 0.251 µL/mL with metabolic activation (Daughtrey et al., 1984; Klimisch score = 1). 0.5 µg/mL triethylenemelamine was used a positive control without metabolic activation and 50 µg/mL cyclophosphamide was used as a positive control with metabolic activation. Negative and positive controls were found to be valid and no significant increase in chromosome aberrations were found. The test substance was however found to be cytotoxic at concentrations of 0.074 µL/mL or greater. The test substance is not clastogenic.

 

In vitro Gene Mutation study in Mammalian Cells

 

Commercial hexane

In a gene mutation study in mammalian cells, CHO cells were exposed to concentrations of 0, 0.132, 0.098, 0.063, 0.0362, or 0.0122 µL/mL both with and without metabolic activation for 5 hours (API, 1990d; Klimisch score =1). The cells were then analyzed for mutation frequency. The test substance was found not to be mutagenic both in the presence and absence of metabolic activation. However, the test substance was cytotoxic at concentrations of 0.063 µL/mL or greater.

In Vivo

 

Commercial hexane

An in vivo study determined the effect of inhalation exposure of commercial hexane (52% n-hexane) on rat bone marrow (Daughtrey et al., 1994; Klimisch score = 1). Groups of 5 male and 5 female rats were exposed to 0, 900, 3000, and 9000 ppm of test substance vapor for 6 hrs/day for 5 days. 0.5 mg/Kg triethylenemelamine was used as a positive control substance. Animals were sacrificed 3 or 21 hours after exposure, and the bone marrow from their femurs examined for cell aberrations. Because no statistically significant increases in cell aberrations were identified, in any of the test groups, the test substance was classified as not mutagenic.

Justification for classification or non-classification

The negative results in in vitro and in vivo genotoxicity assays from a structural analogue do not warrant the classification of 2,3-Dimethylbutane as genotoxic under the new Regulation (EC) 1272/2008 on classification, labeling and packaging of substances and mixtures (CLP).