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EC number: 430-550-0 | CAS number: 1671-49-4
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
Genetic toxicity: in vivo
Administrative data
- Endpoint:
- in vivo mammalian cell study: DNA damage and/or repair
- Remarks:
- Type of genotoxicity: DNA damage and/or repair
- Type of information:
- experimental study
- Adequacy of study:
- key study
- Study period:
- 2012-05-09 to 2013-01-19 (experimental phase)
- Reliability:
- 1 (reliable without restriction)
- Rationale for reliability incl. deficiencies:
- other: Guideline conform study without deviations conducted under GLP
Data source
Reference
- Reference Type:
- study report
- Title:
- Unnamed
- Year:
- 2 013
- Report date:
- 2013
Materials and methods
Test guidelineopen allclose all
- Qualifier:
- according to guideline
- Guideline:
- OECD Guideline 486 (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells in vivo)
- Deviations:
- no
- Qualifier:
- according to guideline
- Guideline:
- EU Method B.39 (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells In Vivo)
- Deviations:
- no
- GLP compliance:
- yes (incl. QA statement)
- Type of assay:
- unscheduled DNA synthesis
Test material
- Reference substance name:
- -
- EC Number:
- 430-550-0
- EC Name:
- -
- Cas Number:
- 1671-49-4
- Molecular formula:
- C8H9NO4S
- IUPAC Name:
- 4-methanesulfonyl-1-methyl-2-nitrobenzene
- Test material form:
- solid: particulate/powder
- Remarks:
- migrated information: powder
- Details on test material:
- - Physical state: off-white powder
- Stability under test conditions: not reported
- Storage condition of test material: At room temperature (< 30 °C)
Constituent 1
Test animals
- Species:
- rat
- Strain:
- Fischer 344
- Sex:
- male/female
- Details on test animals or test system and environmental conditions:
- TEST ANIMALS
- Age at study initiation: 8 to 11 weeks
- Weight at study initiation: males, first experiment: 253.3 g ± 10.9 g (range 228 to 267.6 g); females, first experiment: 159.9 g ± 5.4 g (range 150.5 to 169.9 g); males, second experiment: 241.5 g ± 7.4 g (range 231 to 254.1 g)
- Assigned to test groups randomly: yes
- Fasting period before study: not reported
- Housing: in groups in Makrolon Type III/IV cages with wire mesh top with granulated soft wood bedding
- Diet (e.g. ad libitum): pelleted standard diet ad libitum
- Water (e.g. ad libitum): tap water ad libitum
- Acclimation period: at least five days
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2
- Humidity (%): 45 to > 90 during acclimatization; Relative humidity 45 - 65% during experimental performance
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): 12 hours dark, 12 hours light
IN-LIFE DATES: From: To:
Administration / exposure
- Route of administration:
- oral: gavage
- Vehicle:
- 1% carboxymethylcellulose (CMC)
- Details on exposure:
- PREPARATION OF DOSING SOLUTIONS: on the day of the experiment the test item was suspended in 1% CMC. Grinding in a mortar was necessary to formulate the test item. The test substance was administered as suspension in 1% CMC. the administration volume was 15 mL/kg bw.
- Duration of treatment / exposure:
- Animals received a single dose of substance in vehicle and were observed for up to 16 hours
- Frequency of treatment:
- Single application
- Post exposure period:
- Up to 16 hours
Doses / concentrations
- Remarks:
- Doses / Concentrations:
Males: 400 mg/kg and 800 mg/kg (additional group of 200 mg/kg was included due to high mortality in the 16-hours post-treatment group receiving 800 mg/kg); Females: 250 mg/kg and 500 mg/kg
Basis:
actual ingested
- No. of animals per sex per dose:
- Four
- Control animals:
- yes, concurrent vehicle
- Positive control(s):
- 4 hours preparation interval: N,N'-dimethylhydrazinedihydrochloride (DMH) at 80 mg/kg bw
16 hours preparation interval: 2-acetylaminofluorene (2-AAF)
Examinations
- Tissues and cell types examined:
- Isolated hepatocytes from the livers of test animals
- Details of tissue and slide preparation:
- CRITERIA FOR DOSE SELECTION: a maximum tolerated dose was determined in two pre-experiments, in which the substance was administered by oral gavage to two male and two female animals under the same conditions that were applied in the main test
TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields):
The washed hepatocytes were centrifuged and transferred into Williams medium E supplemented with:
Hepes 2.38 mg/mL
L-Glutamine 0.29 mg/mL
Penicillin 100 units/mL
Insulin 0.50 µg/mL
Streptomycin 0.10 mg/mL
Fetal calf serum (FCS) 100 µL/mL
This complete medium was adjusted to pH 7.6. Three cultures were established from each animal. Aliquots of 2.5 mL with freshly isolated hepatocytes in complete culture medium (200000 viable cells/mL) were added to 35 mm six-well dishes containing one 25 mm round plastic coverslip per well coated with gelatine.
After an attachment period of approximately 1.5 h in a 95 % air/ 5 % CO2 humidified incubator at 37° C the culture medium was discarded. The cell layer was then rinsed once with physiologically buffered saline (PBS) to remove non-adherent cells. Subsequently, 3HTdR (5 µCi/mL, specific activity 70 - 90 Ci/mmol) in 2.0 mL culture medium (Williams medium E (WME), 1 % (v/v) fetal calf serum (FCS)) was added to the cultures. After a labeling time of 4 h the cells were washed twice with WME supplemented with 1 % (v/v) FCS and 0.25 mM unlabeled thymidine. Cultures were incubated overnight using the same medium. To prepare for autoradiography the medium was replaced by a hypotonic solution of 1 % (w/v) sodium citrate for 10 minutes to swell the nuclei for better grain detection. The cells on the coverslips were then fixed by three changes of methanol:acetic acid (3:1 v/v) for 20 minutes each, rinsed with 96 % (v/v) ethanol, and air-dried.
DETAILS OF SLIDE PREPARATION:
The cover slips were mounted on glass slides, cell side upwards and coated with KODAK NTB photographic emulsion in the dark. The coated slides were stored in light-proof boxes in the presence of a drying agent for 14 days at 4°C . The photographic emulsion was then developed at room temperature, fixed in Fixer and stained with hematoxylin/eosin.
METHOD OF ANALYSIS:
Evaluation was performed microscopically on coded slides using microscopes with oil immersion objectives. Slides were examined to ensure sufficient cells of normal morphology were present before analysis. The cells for scoring were randomly selected according to a fixed scheme. The number of silver grains in the nuclear area was counted automatically using the Sorcerer UDS device. In addition, the number of grains of the most heavily labeled nuclear-sized cytoplasm area adjacent to the nucleus was counted. Two slides per animal and 50 cells per slide were evaluated (except for the positive control group of the females with a total of 151 evaluated cells per animal on three slides). Heavily radio-labeled cells undergoing replicative DNA synthesis were excluded from counting.
All animals per group were evaluated as described above, except for the mid dose group of the 4 h preparation interval in male rats and the high dose group of the 16 h preparation interval in female rats where three male animals instead of four animals were evaluated, due to technical reasons during the liver perfusion.
DATA RECORDING
The data generated were recorded in the raw data. The results were presented in tabular form, including experimental groups with the test item, vehicle and positive controls.
The nuclear and cytoplasmic grain counts, the net grain counts (nuclear minus cytoplasmic grains) as well as the mean and percentage of cells in repair (cells with a net grain count larger than 5) is reported separately. Individual slide and animal data are provided. The mean counts with standard deviation are used to describe the distribution of 3HTdR incorporation in the nucleus, the cytoplasm and for the net grains, respectively. - Evaluation criteria:
- Nuclear and net grain counts are estimated together. Increased net grains should be based on enhanced nuclear grain counts rather than on decreased cytoplasmic grain counts.
A test item is classified as positive if the mean number of net grains is higher than five per nucleus at one of the test points.
A group average between 0 and 5 net grains is considered as a marginal positive response. A dose-related increase in nuclear and net grains and/or a substantial shift of the percentage distribution of the nuclear grain counts to higher values provide additional information to confirm a positive response with less than 5 net grains.
Statistical significance may give further evidence for a positive evaluation. Statistical significance can be evaluated by means of the non-parametric Mann-Whitney test.
A test item producing net grains not greater than 0 or not significantly greater than the concurrent control, at any of the test points is considered negative in this system. - Statistics:
- A statistical evaluation of the results was not necessary to perform as the number of net grain counts of the groups treated with the test item were in the range of the corresponding vehicle controls.
Results and discussion
Test results
- Sex:
- male/female
- Genotoxicity:
- negative
- Toxicity:
- yes
- Vehicle controls validity:
- valid
- Positive controls validity:
- valid
- Additional information on results:
RESULTS OF RANGE-FINDING STUDY
- Dose range: first pre-test with 1250 mg/kg in males and 800 mg/kg in females; a second pre-test was conducted due to severe clinical signs occurring in the first pre-test and doses of 800 mg/kg and 500 mg/kg were administered to two male and two female rats, respectively
- Solubility: the substance was suspended in the vehicle
- Clinical signs of toxicity in test animals: first pre-test caused severe clinical signs in animals and two males were sacrificed after 2 to 4 hours and the females were sacrificed moribund after 6 hours
- Rationale for exposure: the oral route was used as this is of relevance to human risk assessment
RESULTS OF DEFINITIVE STUDY
- Appropriateness of dose levels and route: Severe toxicity was noted in the male 800 mg/kg b.w. 16 h treatment group. On this basis additional male treatment groups were dosed at 200 mg/kg b.w., for both time points. Associated positive and negative control groups were also used. Hence, male rats receiving a single oral dose of the substance at dose levels of 200, 400 and 800 mg/kg showed a number of clinical symptoms including reduction of spontaneous activity, abdominal position, ruffled fur, tumbling, apathy, sunken flanks and death (800 mg/kg 16 h only). Female rats receiving a single oral dose of the substance at dose levels of 250 and 500 mg/kg showed a number of clinical symptoms including reduction of spontaneous activity, ruffled fur, sunken flanks, abdominal posture, eyelid closure, tumbling, lacrimation and gasping. the toxic effects seen indicated systemic exposure to the test substance. The animals in the negative and positive control groups did not show any signs of toxicity.
- Statistical evaluation: no statistical evaluation of the results was necessary.
Any other information on results incl. tables
Group means of nucleus, cytoplasmic area and net grains of males
|
Nuclear Grain Count |
Cytoplasmic Grain Count |
Net Grain Counts |
Nuclear Grain Counts of Cells in Repair |
Cells in Repair |
||||
Test Group |
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
% |
|
4 h Preparation Interval |
||||||||
Vehicle control (CMC 1 %) |
22.58 |
11.28 |
38.85 |
14.61 |
-16.27 |
11.97 |
7.67 |
1.62 |
5 |
Vehicle control (CMC 1 %) 2nd experiment |
15.31 |
7.08 |
30.00 |
10.63 |
-14.69 |
9.78 |
2.88 |
0.88 |
1 |
200 mg/kg b.w. test substance 2nd experiment |
20.08 |
7.94 |
32.89 |
12.13 |
-12.81 |
9.93 |
5.40 |
1.23 |
3 |
400 mg/kg b.w. test substance 1st experiment* |
19.29 |
6.99 |
37.54 |
12.67 |
-18.25 |
11.95 |
8.83 |
1.18 |
2 |
800 mg/kg b.w. test substance 1st experiment |
17.07 |
6.60 |
32.62 |
12.14 |
-15.55 |
11.18 |
6.06 |
0.58 |
3 |
positive control (DMH) |
55.90 |
19.65 |
28.01 |
11.64 |
27.88 |
16.88 |
30.05 |
15.42 |
92 |
positive control (DMH) |
72.82 |
21.60 |
32.17 |
11.84 |
40.65 |
18.40 |
42.19 |
16.97 |
96 |
|
16 h Preparation Interval |
||||||||
Vehicle control (CMC 1 %) |
29.33 |
11.54 |
44.45 |
15.66 |
-15.13 |
14.34 |
14.46 |
9.76 |
7 |
Vehicle control (CMC 1 %) 2nd experiment |
24.32 |
10.45 |
41.27 |
14.73 |
-16.95 |
13.76 |
11.06 |
7.06 |
8 |
200 mg/kg b.w. test substance 2nd experiment |
24.14 |
9.12 |
33.31 |
11.09 |
-9.17 |
10.65 |
10.08 |
2.95 |
8 |
400 mg/kg b.w. test substance 1st experiment |
29.04 |
11.70 |
51.79 |
18.50 |
-22.76 |
16.90 |
18.40 |
3.22 |
4 |
800 mg/kg b.w. test substance 1st experiment |
invalid dose group due to high mortality of the treated animals |
||||||||
positive control (2-AAF) |
74.68 |
22.82 |
22.50 |
7.90 |
52.18 |
20.94 |
52.18 |
20.94 |
100 |
positive control (2-AAF) |
33.38 |
11.26 |
21.11 |
9.38 |
12.27 |
10.19 |
16.05 |
8.43 |
76 |
SD=Standard deviation. The standard deviation shown for each animal is the deviation between the 100 analysed cells. The deviation shown for the mean of each group is the mean of the standard deviation obtained for each animal for a group consisting of four animals (* three animals) (test item groups) or two animals (control groups).
Group means of nucleus, cytoplasmic area and net grains of females
|
Nuclear Grain Count |
Cytoplasmic Grain Count |
Net Grain Counts |
Nuclear Grain Counts of Cells in Repair |
Cells in Repair |
||||
Test Group |
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
% |
|
4 h Preparation Interval |
||||||||
Vehicle control (CMC 1 %) |
10.24 |
4.54 |
23.17 |
6.64 |
-12.93 |
7.27 |
2.56 |
1.25 |
2 |
250 mg/kg b.w. test substance |
13.69 |
5.84 |
22.95 |
7.83 |
-9.26 |
8.06 |
8.22 |
1.81 |
4 |
500 mg/kg b.w. test substance |
16.36 |
6.67 |
28.68 |
9.41 |
-12.32 |
9.60 |
5.52 |
1.77 |
4 |
positive control (DMH) |
65.65 |
16.83 |
19.12 |
6.40 |
46.54 |
16.61 |
46.72 |
16.44 |
100 |
|
16 h Preparation Interval |
||||||||
Vehicle control (CMC 1 %) |
17.83 |
9.07 |
36.21 |
12.59 |
-18.38 |
10.96 |
2.75 |
0.50 |
2 |
250 mg/kg b.w. test substance |
18.11 |
8.04 |
31.56 |
10.63 |
-13.45 |
10.91 |
8.44 |
1.56 |
4 |
500 mg/kg b.w. test substance* |
16.80 |
7.14 |
30.36 |
11.17 |
-13.56 |
10.09 |
4.92 |
1.06 |
3 |
positive control (2-AAF) |
31.83 |
12.31 |
27.88 |
10.27 |
3.95 |
10.78 |
13.48 |
7.37 |
44 |
SD=Standard deviation. The standard deviation shown for each animal is the deviation between the 100 analysed cells. the deviation shown for the mean of each group is the mean of the standard deviations obtained for each animal for a group consisting of four animals (* three animals) (test item groups) or two animals (control groups).
Viability and number of hepatocytes for the males, 4 h timepoint
Treatment |
Period |
Animal no. |
Viability*[%] |
Number of isolated cells [x106] |
|
1 % CMC (1stmain experiment) |
4 h |
1 |
62 |
158 |
|
2 |
78 |
351 |
|||
1 % CMC (2ndmain experiment) |
4 h |
49 |
69 |
267 |
|
50 |
78 |
246 |
|||
200 mg/kg b.w. Test substance |
4 h |
51 |
89 |
318 |
|
52 |
77 |
244 |
|||
53 |
76 |
211 |
|||
54 |
78 |
160 |
|||
400 mg/kg b.w. Test substance |
4 h |
3 |
81 |
88.5 |
|
4 |
68 |
233 |
|||
5 |
73 |
210 |
|||
6 |
Perfusion failed |
||||
800 mg/kg b.w. Test substance |
4 h |
7 |
62 |
212 |
|
8 |
65 |
374 |
|||
9 |
70 |
186 |
|||
10 |
68 |
281 |
|||
80 mg/kg b.w. DMH (1stmain experiment) |
4 h |
11 |
75 |
255 |
|
12 |
85 |
302 |
|||
80 mg/kg b.w. DMH (2ndmain experiment) |
4 h |
55 |
78 |
265 |
|
56 |
75 |
233 |
* Viability determined by means of trypan blue dye exclusion assay
Viability and number of hepatocytes for the males, 16 h timepoint
Treatment |
Period |
Animal no. |
Viability*[%] |
Number of isolated cells [x106] |
|
1 % CMC (1stmain experiment)
|
16 h |
13 |
72 |
306 |
|
14 |
90 |
266 |
|
||
1 % CMC (2ndmain experiment)
|
16 h |
57 |
83 |
251 |
|
58 |
80 |
228 |
|
||
200 mg/kg b.w. Test substance
|
16 h |
59 |
82 |
223 |
|
60 |
81 |
134 |
|
||
61 |
78 |
425 |
|
||
62 |
73 |
226 |
|
||
400 mg/kg b.w. Test substance
|
16 h |
15 |
90 |
232 |
|
16 |
82 |
215 |
|
||
17 |
83 |
255 |
|
||
18 |
88 |
282 |
|
||
800 mg/kg b.w. Test substance
|
16 h |
19 |
Invalid dose group due to high mortality of the treated animals |
|
|
20 |
|
||||
21 |
|
||||
22 |
|
||||
100 mg/kg b.w. 2-AAF (1stmain experiment)
|
16 h |
23 |
86 |
275 |
|
24 |
83 |
278 |
|
||
100 mg/kg b.w. 2-AAF (2ndmain experiment)
|
16 h |
63 |
75 |
306 |
|
64 |
65 |
258 |
|
* Viability determined by means of trypan blue dye exclusion assay
Viability and number of hepatocytes for the females, 4 h timepoint
Treatment |
Period |
Animal no. |
Viability*[%] |
Number of isolated cells [x 106] |
1 % CMC |
4 h |
25 |
81 |
75 |
26 |
71 |
147 |
||
250 mg/kg b.w. Test substance
|
4 h |
27 |
57 |
85.5 |
28 |
78 |
318 |
||
29 |
59 |
103 |
||
30 |
79 |
154 |
||
500 mg/kg b.w. Test substance
|
4 h |
31 |
72 |
205 |
32 |
82 |
269 |
||
33 |
74 |
196 |
||
34 |
65 |
83 |
||
80 mg/kg b.w. DMH |
4 h |
35 |
90 |
196 |
36 |
80 |
270 |
* Viability determined by means of trypan blue dye exclusion assay
Viability and number of hepatocytes for the females, 16 h timepoint
Treatment |
Period |
Animal no. |
Viability*[%] |
Number of isolated cells [´ 106] |
|
1 % CMC |
16 h |
37 |
85 |
230 |
|
38 |
75 |
174 |
|
||
250 mg/kg b.w. Test substance
|
16 h |
39 |
85 |
159 |
|
40 |
79 |
142 |
|
||
41 |
80 |
130 |
|
||
42 |
80 |
128 |
|
||
500 mg/kg b.w. Test substance
|
16 h |
43 |
81 |
152 |
|
44 |
Perfusion failed |
|
|||
45 |
62 |
174 |
|
||
46 |
80 |
162 |
|
||
100 mg/kg b.w. 2-AAF |
16 h |
47 |
75 |
203 |
|
48 |
66 |
127 |
|
* Viability determined by means of trypan blue dye exclusion assay
Applicant's summary and conclusion
- Conclusions:
- Interpretation of results (migrated information): negative
Under the experimental conditions, i.e. oral administration up to 800 mg/kg for males and up to 500 mg/kg for females, the test item did not induce DNA-damage leading to increased repair synthesis in the hepatocytes of the treated rats. Therefore, the substance is considered to be non-genotoxic in this in vivo UDS test system. - Executive summary:
The substance was assessed under GLP in this valid in vivo UDS assay for its potential to induce unscheduled DNA repair (UDS) in the hepatocytes of rats according to OECD TG 486 with doses of 200, 400 and 800 mg/kg bw for males and 250 and 500 mg/kg bw for females after post treatment intervals of 4 and 16 hours. The highest dose, i.e. the maximum tolerated dose leading to acceptable clinical symptoms, was established in two pre-experiments. The test item was suspended in 1% carboxymethylcellulose, which was also used as the vehicle control. The volume administered orally was 15 mL/kg body weight. After single oral treatment and a post-treatment period of 4 or 16 hours the animals were sacrificed by terminal anaesthesia. The livers were then perfused. Primary hepatocytes wee established and exposed for 4 hours to 3HTdR, which is incorporated if UDS occurs.
The viability of the hepatocytes was not substantially affected by the in vivo treatment with the test substance at any of the treatment periods or dose groups. The interindividual variations obtained for the numbers and the viability of the isolated hepatocytes were in the range of the laboratory historical control data. All viabilities were greater than the OECD TG recommended viability of > 50%.
No UDS induction in the hepatocytes of the male and female rats treated with a single oral dose of the test substance as compared to the animals of the concurrent vehicle controls was observed at 200, 400 and 800 mg/kg bw for male rats and at 250 and 500 mg/kg bw for female rats. The nuclear grain counts and the resulting net grain counts were not distinctly enhanced due to the in vivo treatment of the animals with the test item after 4 hours and 16 hours post treatment. Therefore, the mean net grain counts obtained after treatment with the the substance were consistently negative. As no UDS response was observed statistical analysis of the data was not performed. No substantial shift to higher values was obtained in the percentage of cells in repair, which confirms the lack of UDS.
Appropriate reference mutagens (N,N'-dimethylhydrazinedihydrochloride at 80 mg/kg bw and 2-acetylaminofluorene at 100 mg/kg bw) produced distinct increases in the number of nuclear and net grain counts, indicating UDS. Additionally, the percentage of cells in repair was significantly increased, which is consistent with a UDS response. The positive control at the 16 hour preparation interval of the female animals showed a mean net grain count of 3.95 being below the optimal value of 5 net grain counts indicating nominally used in this laboratory to indicate a positive result but within the laboratory historical control data range for similar studies and distinctly different to the strongly negative values observed for the negative control groups. Additionally, as 44% of the cells were in repair (compared to 1.5% of the cells in the vehicle control) the positive control response is considered as valid.
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