Registration Dossier

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Studies of bacterial mutation (Ames tests), mamalian cell mutation in vitro and mammalian cell clastogenicity in vitro are available for fenitrothion.

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Not reported: published study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
GLP compliance:
no
Type of assay:
bacterial reverse mutation assay
Specific details on test material used for the study:
Fenitrothion technical grade
Batch No.: 00106
Purity: 94.7%
Target gene:
Various; reversion to histidine and tryptophan independence
Species / strain / cell type:
S. typhimurium TA 1535, TA 1537, TA 98 and TA 100
Species / strain / cell type:
other: TA100NR
Remarks:
nitroreductase-deficient
Species / strain / cell type:
E. coli WP2 uvr A
Species / strain / cell type:
other: TA100 1,8-DNP6
Remarks:
transacetylase deficient
Metabolic activation:
with and without
Metabolic activation system:
S9 from Sprague-Dawley rats treated intraperitoneally with polychlorinated biphenyls (PCB)
Test concentrations with justification for top dose:
0, 100, 200, 500, 1000, 2000, 5000 ug/plate (limit concentration)
Vehicle / solvent:
DMSO
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
9-aminoacridine
2-nitrofluorene
sodium azide
benzo(a)pyrene
methylmethanesulfonate
other: 2-aminoanthracene, 2, 80 ug/plate
Details on test system and experimental conditions:
Fenitrothion was tested using strains of Salmonella typhimurium (TA98, TA100, TA1535, TA1537, TA100 NR (nitroreductase-deficient strain) and TA100 1,8 -DNP6 (transacetylase-deficient strain)); and Escherichia coli WP2uvrA. Purified samples of fenitrothion and aminofenitrothion (AM-FNT) were tested using strains TA98, TA100, TA100 NR and TA100 1,8 -DNP6. Fenitrooxon (FNO), nitrosofenitrothion, nitrosofenitrooxon, aminofenitrooxon (AM-FNO) and 3-methyl-4-nitrophenol (NMC), were tested using strains TA98 and TA100. Test chemicals were dissolved in DMSO and tests were conducted using a pre-incubation method with and without metabolic activation. Negative control (DMSO, 100 ul /plate), positive and insensitive controls were also tested with and without metabolic activation. S9 mix, a mixture of cofactors and the liver S9 from Sprague-Dawley rats treated intraperitoneally with polychlorinated biphenyls (PCB), were used for metabolic activation.
Statistics:
Not required
Key result
Species / strain:
S. typhimurium TA 98
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1537
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 100
Remarks:
weak mutagenicity was observed only in TA100 and it was enhanced by the addition of S9 mix
Metabolic activation:
with and without
Genotoxicity:
positive
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
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
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
other: TA100NR
Remarks:
nitroreductase deficient
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
other: TA100 1,8-DNP6
Remarks:
transacetylase deficient strain
Metabolic activation:
with and without
Genotoxicity:
positive
Remarks:
Decreased compared to TA100
Cytotoxicity / choice of top concentrations:
cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
Fenitrothion showed weak mutagenicity in TA100 without S9 and its mutagenicity was slightly enhanced by the addition of S9. The mutagenic activity of the technical-grade sample of fenitrothion did not differ from that of the purified sample. The mutagenicity of fenitrothion was not detected in TA100 NR, and was decreased in TA100 1,8-DNP6.

Summary of results

Chemical

Dose

(mg/plate)

Revertant colonies/plate

Salmonella typhimurium

TA100

TA100 NR

TA100 1,8-DNP6

-S9

+S9

-S9

+S9

-S9

+S9

Fenitrothion

(technical)

0

94

87

114

100

108

105

100

113

122

107

104

126

120

200

138

173

101

111

127

131

500

192

323

110

105

141

145

1000

203t

380

105t

104

152t

160

2000

173t

315t

97t

103

154t

184

5000

142t

173t

90t

101

174t

215

Fenitrothion

(purified)

0

81

79

87

83

96

89

100

116

121

81

93

104

104

200

153t

164

88

96

113t

112

500

224t

341

102

105

125t

128

1000

224t

388t

89t

82

123t

141

2000

222t

463t

86t

89

135t

146

5000

221t

255t

80t

91

134t

154

MMS

100

413

-

468

-

514

-

B(a)P

5

-

827

-

949

-

964

2NF

2

485

-

154

-

176

-

1,8-DNP

0.01

473

-

771

-

151

-

t: evidence of toxicity

Chemical

Dose

(mg/

plate)

Revertant colonies/plate

Salmonella typhimurium

Escherichia coli

TA98

TA1535

TA1537

WP2uvrA

-S9

+S9

-S9

+S9

-S9

+S9

-S9

+S9

Fenitrothion

(technical)

0

37

38

10

10

11

21

16

15

100

32

36

9

10

8

14

19

21

200

34

38

8

14

10

17

18

25

500

34

44

9

15

5

12

25

20

1000

31

40

7

13

4t

4t

24

22

2000

26

37

9

9

3t

3t

22

21

5000

21

39

7

8

3t

3t

23

25

Fenitrothion

(purified)

0

25

44

-

-

-

-

-

-

100

28

32

-

-

-

-

-

-

200

30

35

-

-

-

-

-

-

500

25

44

-

-

-

-

-

-

1000

35t

42

-

-

-

-

-

-

2000

22t

37

-

-

-

-

-

-

5000

22t

37

-

-

-

-

-

-

2NF

1

355

-

-

-

-

-

-

-

2

-

-

-

-

-

-

250

 

B(a)P

5

-

687

-

-

-

160

-

-

Sodium azide

0.5

-

-

341

-

-

-

-

-

2AA

2

-

-

-

141

-

-

-

-

80

-

-

-

-

-

-

-

479

9AA

80

-

-

-

-

1474

-

-

-

t: evidence of toxicity

Chemical

Dose

(mg/plate)

 Revertant colonies/plate

Salmonella typhimurium

TA100

TA100NR

TA100 1,8-DNP6

TA98

-S9

+S9

-S9

+S9

-S9

+S9

-S9

+S9

FNO

0

 71

 66

-

-

-

-

23

34

3

 71

 69

-

-

-

-

31

39

10

 78

 63

-

-

-

-

25

41

30

83

69

-

-

-

-

24

36

100

83

72

-

-

-

-

20

40

300

91

101

-

-

-

-

36

49

1000

 165

204

-

-

-

-

33

43

Nitroso-

fenitrothion

0

93

89

-

-

-

-

26

40

2

106

86

-

-

-

-

38

40

5

133

86

-

-

-

-

32

44

10

118t

92

-

-

-

-

4t

38

20

73t

113

-

-

-

-

Tox

53

50

Tox

111

-

-

-

-

-

56

100

-

103

-

-

-

-

-

59

200

-

117

-

-

-

-

-

58

500

-

Tox

-

-

-

-

-

151

Nitroso-

fenitrooxon

0

71

66

-

-

-

-

23

34

3

82

57

-

-

-

-

38

38

10

90

72

-

-

-

-

29

42

30

42t

99

-

-

-

-

17t

40

100

Tox

106

-

-

-

-

Tox

49

300

-

97

-

-

-

-

-

48

1000

-

Tox

-

-

-

-

-

Tox

AM-FNT

0

83

64

104

97

132

112

30

46

2

86

85

104

115

126

121

-

-

5

96

118

109

145

124

137

-

-

10

92

158

102

189

131

161

-

-

20

78

225

110

244

119

181

-

-

50

79

294

118

304

115

216

-

-

100

88

355

113

332

119

205

32

65

200

-

-

-

-

-

-

25

76

500

38t

344

94t

373

123t

220

29

69

1000

Tox

285t

Tox

393

89t

261

15t

58

5000

-

-

-

-

-

-

Tox

Tox

AM-FNO

0

71

66

-

-

-

-

23

34

3

77

63

-

-

-

-

37

46

10

64

60

-

-

-

-

35

41

30

70

64

-

-

-

-

26

38

100

61

115

-

-

-

-

26

37

300

83

221

-

-

-

-

25

63

1000

96

290

-

-

-

-

34

60

NMC

0

94

100

-

-

-

-

27

49

50

85

103

-

-

-

-

31

49

100

88

92

-

-

-

-

24

42

200

86

47

-

-

-

-

31

40

500

100

61

-

-

-

-

27

35

1000

45

38

-

-

-

-

12

26

2000

Tox

Tox

-

-

-

-

Tox

3

t: evidence of toxicity

Tox: excessive toxicity, not scored

Conclusions:
Fenitrothion was found to be non-mutagenic in TA98, TA1535, TA1537 and WP2uvrA both with and without S9 mix, while weak mutagenicity was observed only in TA100 and it was enhanced by the addition of S9 mix. The mutagenicity was not observed in a nitroreductase-deficient strain, TA100 NR, and it decreased in a transacetylase-deficient strain, TA100 1,8-DNP6. The results suggest that the bacterial nitroreductase activity is necessary for fenitrothion to express the mutagenicity in TA100.
Executive summary:

The mutagenic potenitial of fenitrothion was investigated in an Ames test. Fenitrothion was tested using strains of Salmonella typhimurium (TA98, TA100, TA1535, TA1537, TA100 NR (nitroreductase-deficient strain) and TA100 1,8 -DNP6 (transacetylase-deficient strain)); and Escherichia coli WP2uvrA. Purified samples of fenitrothion and aminofenitrothion (AM-FNT) were tested using strains TA98, TA100, TA100 NR and TA100 1,8 -DNP6. Fenitrooxon (FNO), nitrosofenitrothion, nitrosofenitrooxon, aminofenitrooxon (AM-FNO) and 3-methyl-4-nitrophenol (NMC), were tested using strains TA98 and TA100. Test chemicals were dissolved in DMSO and tests were conducted using a pre-incubation method with and without metabolic activation. Negative control (DMSO, 100 ul /plate), positive and insensitive controls were also tested with and without metabolic activation. S9 mix, a mixture of cofactors and the liver S9 from Sprague-Dawley rats treated intraperitoneally with polychlorinated biphenyls (PCB), were used for metabolic activation. Fenitrothion was found to be non-mutagenic in TA98, TA1535, TA1537 and WP2uvrA both with and without S9 mix, while weak mutagenicity was observed only in TA100 and it was enhanced by the addition of S9 mix. The mutagenicity was not observed in a nitroreductase-deficient strain, TA100 NR, and it decreased in a transacetylase-deficient strain, TA100 1,8-DNP6. The results suggest that the bacterial nitroreductase activity is necessary for fenitrothion to express the mutagenicity in TA100.

Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Study period:
25 March 1986 - 23 May 1986
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
EU Method B.17 (Mutagenicity - In Vitro Mammalian Cell Gene Mutation Test)
GLP compliance:
yes
Type of assay:
in vitro mammalian cell gene mutation test using the Hprt and xprt genes
Specific details on test material used for the study:
Fenitrothion
Batch No.: 00106
Purity: 94.7%
Target gene:
HPRT
Species / strain / cell type:
Chinese hamster lung fibroblasts (V79)
Metabolic activation:
with and without
Metabolic activation system:
Kanechlor 400-induced male SD rat liver S9 fraction
Vehicle / solvent:
DMSO
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO 1%
True negative controls:
no
Positive controls:
yes
Positive control substance:
7,12-dimethylbenzanthracene
other: N-methyl-N’-nitro-N-nitrosoguanidine (-S9)
Details on test system and experimental conditions:
In the main gene mutation test, cultures of V79 cells were treated with fenitrothion at concentrations of 10e-5 M, 3×10e-5 M, 10e-4 M and 3×10e-4 M with and without S9. Fenitrothion was dissolved in dimethyl sulphoxide (DMSO). Negative (sovent) controls (DMSO 1%) and positive controls (N-methyl-N’-nitro-N-nitrosoguanidine 3×10e-6 M; 9,10 -dimethyl-1,2 -benzanthracene 3×10e-5 M) were run concurrently. After incubation for five hours at 37°C, the cells were washed and cultured to determine cytotoxicity and to allow for expression of the mutant phenotype at 37°C for 7 days. After the expression period, the cells were innoculated to dishes with and without 6-thioguanine (6-TG) and cultivated for 6 or 7 days to determine the number of mutants and plating efficiency. Colonies formed were fixed, Giemsa-stained and counted. The number of colonies for each dish was counted and the mutation frequency and the plating efficiency were calculated.
Rationale for test conditions:
To determine appropriate concentrations for use in the gene mutation test, a preliminary cytotoxicity test was performed using concentrations of 10e-3 to 10e-5 M with a dilution factor of 3 in the presence and absence of metabolic activation system (S9 mix).
Evaluation criteria:
Not reported
Statistics:
Appropriate statisitcal methods were used to compare the control and treated groups
Key result
Species / strain:
Chinese hamster lung fibroblasts (V79)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
precipitation also observed
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid

Summary of findings (-S9)

 

Chemical

Concentration

Experiment 1

Experiment 2

Survival (%)

Plating efficiency (%)

Mutation frequency (/10e6)

Survival (%)

Plating efficiency (%)

Mutation frequency (/10e6)

DMSO

1.0%

100

105.6

1.6

100

75.0

4.9

 

-

-

-

 

88.8

5.3

Fenitrothion

10e-5M

111

98.4

4.4*

89

88.6

5.3

3x10e-5M

94

101.8

5.6**

97

97.8

6.5

10e-4M

81

110.0

7.6**

80

89.6

5.6

3x10e-4M p

66

114.0

6.4**

70

80.0

8.3

MNNG

3x10e-6M

86

76.5

1063.5**

76

60.6

1234.3**

*significantly different to controls (p<0.05); **p<0.01

Summary of findings (+S9)

 

Chemical

Concentration

Experiment 1

Experiment 2

Survival (%)

Plating efficiency (%)

Mutation frequency (/10e6)

Survival (%)

Plating efficiency (%)

Mutation frequency (/10e6)

DMSO

1.0%

100

112.6

3.3

100

85.4

0.8

-

-

-

97.0

2.7

Fenitrothion

10e-5M

94

100.6

6.6*

92

100.0

4.0

3x10e-5M

98

97.0

6.2

89

92.6

3.2

10e-4M

87

82.2

6.5

89

107.4

2.5

3x10e-4M p

64

101.4

7.2*

62

90.2

5.2*

DMBA

3x10e-5M

85

106.2

178.0**

82

71.6

260.2**

*significantly different to controls (p<0.05); **p<0.01

Conclusions:
Small increases in the mutation frequencies are considered to be within the range of variation of the spontaneous mutation frequency, and no reproducible dose-response relationship were observed both in the presence and absence of metabolic activation. Fenitrothion was concluded not mutagenic under the test conditions.
Executive summary:

The mutagenic potential of fenitrothion was investigated in an HPRT assay using V79 cells. To determine appropriate concentrations for use in the gene mutation test, a preliminary cytotoxicity test was performed using concentrations of 10e-3 to 10e-5 M with a dilution factor of 3 in the presence and absence of metabolic activation system (S9 mix). In the main study, cultures of V79 cells were treated with fenitrothion at concentrations of 10e-5 M, 3×10e-5 M, 10e-4 M and 3×10e-4 M with and without S9. Fenitrothion was dissolved in dimethyl sulphoxide (DMSO). Negative (sovent) controls (DMSO 1%) and positive controls (N-methyl-N’-nitro-N-nitrosoguanidine 3×10e-6 M; 9,10 -dimethyl-1,2 -benzanthracene 3×10e-5 M) were run concurrently. After incubation for five hours at 37°C, the cells were washed and cultured to determine cytotoxicity and to allow for expression of the mutant phenotype at 37°C for 7 days. After the expression period, the cells were innoculated to dishes with and without 6-thioguanine (6-TG) and cultivated for 6 or 7 days to determine the number of mutants and plating efficiency. Colonies formed were fixed, Giemsa-stained and counted. The number of colonies for each dish was counted and the mutation frequency and the plating efficiency were calculated.

In the first experiment without metabolic activation, the mutation frequencies of the fenitrothion-treated groups were statistically significantly higher than that of the negative control group, but no concentration-dependent increase was observed. The result in the second experiment with two negative control groups showed no significant differences. In the first experiment with metabolic activation, the mutation frequencies of the fenitrothion-treated groups were partly higher than that of the negative control group, but no concentration-dependent increase was observed. In the second experiment, a small increase was observed at the highest concentration in the mutation frequency, but these values were within the range of historical control data [range (0.8-7.7) ×10-6; average (4.3 +/- 2.0) ×10e-6 (n=12)]. Small increases in the mutation frequencies are considered to be within the range of variation of the spontaneous mutation frequency, and no reproducible dose-response relationship were observed both in the presence and absence of metabolic activation. Fenitrothion was concluded not mutagenic under the test conditions.

Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Study period:
14 April 1988 - 7 June 1988
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)
GLP compliance:
yes
Type of assay:
in vitro mammalian chromosome aberration test
Specific details on test material used for the study:
Fenitrothion
Batch No.: 60553
Purity: 96.7%
Target gene:
Not applicable (clastogenicity study)
Species / strain / cell type:
Chinese hamster Ovary (CHO)
Remarks:
CHO-K!
Cytokinesis block (if used):
Colcemid (0.1 ug/mL) was added to cultures two hours prior to harvest
Metabolic activation:
with and without
Metabolic activation system:
Kanechlor-400 induced male SD rat liver S9
Test concentrations with justification for top dose:
3, 10 and 30 µg/ml, for 8, 16 or 24 hours
Vehicle / solvent:
DMSO
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO 0.5%
True negative controls:
no
Positive controls:
yes
Positive control substance:
benzo(a)pyrene
cyclophosphamide
mitomycin C
Statistics:
Appropriate statistical methods were uased to compare the control and test material groups.
Key result
Species / strain:
Chinese hamster Ovary (CHO)
Remarks:
CHO-K1
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
not determined
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid

Summary of clastogenicity (-S9)

8 hr treatment

Treatment

µg/mL

Cells scored

Chromosomal aberration

Total aberrations

Cells with aberrations(%)

Polyploid (%)

 

MI (%)

ctg

ctb

cte

csg

csb

cse

Oth

+ G

- G

+ G

- G

DMSO

0.5

100

0

0

0

0

0

0

0

0

0

0

0

2

8.0

%

100

0

1

0

0

1

1

0

3

3

3

3

1.5

9.6

Fenitrothion

3

100

0

0

0

0

0

0

0

0

0

0

0

3.5

6.7

100

0

1

0

0

0

0

0

1

1

1

1

3

7.0

10

100

1

1

1

0

0

0

0

3

2

3

2

3

7.0

100

0

1

0

0

0

0

0

1

1

1

1

6*

8.2

30

100

1

1

0

0

0

1

0

3

2

2

2

2.5

2.4

100

1

0

0

0

0

0

0

1

0

1

0

1.5

2.6

MMC

0.05

100

1

0

0

0

0

0

0

1

0

1

0

0.5

3.5

 

 

100

1

1

2

0

0

2

0

6

5

5

5

3

4.2

16 hr treatment

Treatment

µg/mL

Cells scored

Chromosomal aberration

Total aberrations

Cells with aberrations(%)

Polyploid (%)

 

MI (%)

ctg

ctb

cte

csg

csb

cse

Oth

+ G

- G

+ G

- G

DMSO

0.5

100

0

0

0

0

0

1

0

1

1

1

1

1

7.5

%

100

0

0

1

0

0

0

0

1

1

1

1

1

6.5

Fenitrothion

3

100

0

1

0

0

0

0

0

1

1

1

1

2

6.6

100

0

1

0

0

0

0

0

1

1

1

1

2

7.0

10

100

0

1

0

0

0

0

0

1

1

1

1

0

6.9

100

0

0

1

0

0

1

0

2

2

2

2

0

6.1

30

100

2

1

0

0

0

0

0

3

1

3

1

1.5

4.2

100

0

0

0

0

0

0

0

0

0

0

0

1

4.0

MMC

0.05

100

2

11

12

0

0

0

1

26**

24**

21**

19**

0.5

2.8

100

4

8

11

0

0

0

0

23**

19**

18**

16**

1

3.8

24 hr treatment

Treatment

µg/mL

Cells scored

Chromosomal aberration

Total aberrations

Cells with aberrations(%)

Polyploid (%)

 

MI (%)

ctg

ctb

cte

csg

csb

cse

Oth

+ G

- G

+ G

- G

DMSO

0.5

100

1

1

0

0

0

0

0

2

1

2

1

1.5

6.2

%

100

0

1

0

0

0

0

0

1

1

1

1

0.5

5.0

Fenitrothion

3

100

0

0

0

0

0

2

0

2

2

2

2

1

6.1

100

0

0

0

0

0

0

0

0

0

0

0

1.5

5.5

10

100

0

7

0

0

0

1

0

8

8

2

2

3.5

6.0

100

1

0

0

0

1

1

0

3

2

3

2

1

5.8

30

100

0

0

0

0

0

0

0

0

0

0

0

2

2.0

100

0

0

0

0

0

0

0

0

0

0

0

2.5

2.4

MMC

0.05

100

6

15

29

0

0

3

0

53**

47**

41**

37**

1

3.4

100

5

13

23

0

1

1

0

43**

38**

37**

34**

1

2.9

ctg: chromatid gaps

ctb: chromatid breaks

cte: chromatid exchanges

csg: chromosome gaps

csb: chromosome breaks

cse: chromosome exchanges

Oth: others (fragmentations and cells with more than 9 aberrations)

+G: aberrations including gaps

-G: aberrations excluding gaps

*p<0.05; **p<0.01

Summary of clastogenicity (+S9)

 

2 hr treatment and 14 hr culture

Treat-ment

Dose (µg/ml)

Cells scored

Chromosomal aberrations

Total aberrations

Cells with aberrations (%)

Polyploidy (%)

 

MI (%)

ctg

ctb

cte

csg

csb

cse

Oth

+ G

- G

+ G

- G

DMSO

0.5

100

1

1

0

0

0

0

0

2

1

2

1

1.5

3.3

%

100

3

0

0

0

0

1

0

4

1

4

1

2

2.6

Fenitrothion

75

100

2

1

0

0

0

0

0

3

1

3

1

1.5

3.8

 

100

2

1

2

0

1

1

0

7

5

5

4

2.5

4.4

150

100

0

0

0

0

0

0

0

0

0

0

0

2.5

3.0

 

100

0

1

1

0

0

0

0

2

2

2

2

1

2.7

300

100

0

0

0

0

0

0

0

0

0

0

0

1

1.7

 

100

0

1

2

0

0

0

0

3

3

2

2

1.5

2.2

B(a)P

20

100

1

5

32

0

0

0

0

38**

37**

33**

32**

1

3.2

 

100

2

5

34

0

0

1

0

42**

40**

37**

35**

1.5

2.4

2 hr treatment and 22 hr culture

Treat-ment

Dose (µg/ml)

Cells scored

Chromosomal aberrations

Total aberrations

Cells with aberrations (%)

Polyploidy (%)

 

MI (%)

ctg

ctb

cte

csg

csb

cse

Oth

+ G

- G

+ G

- G

DMSO

0.5

100

0

0

1

0

0

0

0

1

1

1

1

2

6.3

%

100

1

0

0

0

0

0

0

1

0

1

0

1.5

6.1

Fenitrothion

75

100

0

0

1

0

0

0

0

1

1

1

1

1.5

6.1

100

0

2

0

0

0

2

0

4

4

4

4

1

6.0

150

100

0

0

1

0

0

1

1

3

3

3

3

2

2.7

100

0

1

0

0

0

0

0

1

1

1

1

2

2.6

300

100

0

0

2

0

0

0

0

2

2

2

2

1.5

2.5

100

0

1

2

0

0

0

0

3

3

1

1

1

1.7

CP

40

100

5

10

39

0

2

0

1

57**

52**

32**

29**

1

2.4

100

3

10

31

0

2

1

1

48**

45**

34**

32**

1.5

1.9

ctg: chromatid gaps

ctb: chromatid breaks

cte: chromatid exchanges

csg: chromosome gaps

csb: chromosome breaks

cse: chromosome exchanges

Oth: others (fragmentations and cells with more than 9 aberrations)

+G: aberrations including gaps

-G: aberrations excluding gaps

*p<0.05; **p<0.01

Conclusions:
Fenitrothion does not have any clastogenic potential against CHO-K1 cells under the conditions tested.
Executive summary:

The potential clastogenicity of fenitrothion was investigated in CHO-K1 cells. A preliminary cytotoxicity test was performed to determine the concentrations to be used in the main study. The concentrations ranged from 1 -300 µg/mL with and without metabolic activation. In the chromosomal aberration test, Chinese hamster ovary cells (CHO-K1) were treated with fenitrothion (dissolved in DMSO) at concentrations of 3, 10 and 30 µg/mL for periods of 8, 16 or 24 hours in the absence of metabolic activation. In the presence of metabolic activation, cells were exposed to concentrations of 75, 150 and 300 µg/mL for 2 hours, with further culture in a fresh medium for 14 or 22 hours after removal of the test chemical. The cells were harvested, fixed, stained and analyzed in a blind manner. Negative control (DMSO) and positive controls (MMC, B(a)P, cyclophosphamide) were also tested. Mitotic indices were determined by counting more than 1000 cells. The number of structural aberrations and the frequencies of cells with structural aberrations were obtained by observation of 100 cells from each duplicate culture at each experimental point, and also the frequencies of polyploid cells were determined by observation of an additional 200 cells. Fenitrothion did not induce any significant increase in the number of total chromosome aberrations or in the frequency of cells with structural aberrations in the presence or absence of metabolic activation. A slight increase in the incidence of polyploid cells was observed in one culture of the 8 -hour treatment group at a concentration of 10 µg/ml in the absence of metabolic activation. However, no significant increase of polyploid cells was observed in other cultures and time- or concentration-dependency was not observed. Thus it was concluded that the increase was spontaneous. Positive control chemicals induced marked increases both in the number of total chromosome aberrations and in the frequency of cells with chromosomal aberrations. Fenitrothion does not have any clastogenic potential against CHO-K1 cells under the conditions tested.

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
17 October 1975
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
significant methodological deficiencies
Qualifier:
no guideline followed
Principles of method if other than guideline:
In house method (Ames test), significant deficiencies compared to OECD 471
GLP compliance:
no
Type of assay:
bacterial reverse mutation assay
Specific details on test material used for the study:
Fenitrothion
Batch No.: 31184
Purity: 98.5%
Target gene:
Various; reversion to histidine and tryptopgan independence
Species / strain / cell type:
S. typhimurium TA 1535
Species / strain / cell type:
S. typhimurium TA 1537
Species / strain / cell type:
S. typhimurium TA 1538
Species / strain / cell type:
E. coli, other:
Details on mammalian cell type (if applicable):
W-3102
Metabolic activation:
with and without
Metabolic activation system:
Liver, lung, kidney, testis and brain homogenate from male SD rats intraperitoneally injected with 3-methylcholanthrene (20 mg/kg) for 24 hr and liver homogenate from male ICR mice pretreated with 1% sodium phenobarbital in drinking water for one week
Test concentrations with justification for top dose:
10, 100, 1000, 10000 ug/plate (exceeds limit concentration)
Vehicle / solvent:
DMSO
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
Remarks:
DMSO
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: N-methyl-N’-nitro-N-nitrosoguanidine; 2-aminoanthracene
Remarks:
NNG: used for all strains without metabolic activation; 2-AA used for all strains with metabolic activation
Details on test system and experimental conditions:
Salmonella typhimurium (strains TA1535 his G-, TA1537 his D-, TA1538 his C- uvr B-) and Escherichia coli (W3102 trp E -) cultures were treated with fenitrothion) dissolved in dimethyl sulfoxide (DMSO) (10 ul /plate or 100 ul/tube without metabolic activation, 100 ul/plate with metabolic activation) at dose levels of 10, 100, 1000 (with and without metabolic activation) and 10000 (without metabolic activation) ug/plate or 10, 100, 1000 ug/ ml (without metabolic activation). Negative control (DMSO, 10000 ug/plate or 100 ul/tube) and positive controls (N-methyl-N’-nitro-N-nitrosoguanidine (NTG): 10, 100, 1000 ug/ plate; 2-aminoanthracene: 100, 1000 ug/ plate) were also tested with and without metabolic activation.

Three plates were used for each treatment,

1) Without metabolic activation; a) Bacterial cells were inoculated on the minimal plate and the test chemicals were applied onto a paper disk. Plates were incubated at 37°C for 48 hours. The number of revertant colonies per plate was counted. b) Bacterial suspension were mixed with the test chemicals. The mixture was incubated at 37°C for 1 hour. Bacterial cells were washed and plated to determine the viability and the mutation frequency, respectively. Reverse mutant cells and viable cells were counted respectively, and mutation frequency was calculated.

2) With metabolic activation; The metabolizing mixture containing the homogenate (Liver, lung, kidney, testis and brain homogenate from male Sprague Dawley rats intraperitoneally injected with 3-methylcholanthrene (20 mg/kg) for 24 hr and liver homogenate from male ICR mice pretreated with 1% sodium phenobarbital in drinking water for one week), bacterial cells and the test chemicals was shaken for 30 min at 37°C. The whole mixture was plated and incubated for 48 hours at 37°C. The number of revertant colonies per plate was counted.
Statistics:
Not required
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
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
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
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
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 nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid
Key result
Species / strain:
other: W-3102
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Vehicle controls validity:
valid
Untreated negative controls validity:
not applicable
Positive controls validity:
valid

Summary of results without metabolic activation

Chemical

Dose (mg/ plate)

Revertant colonies/plate

E. coli

S. typhimurium

W-3102

TA1535

TA1537

TA1538

DMSO

10000

23.0

13.3

10.7

46.7

Fenitrothion

10

16.6

10.7

21.0

46.7

100

30.0

7.30

16.3

29.7

1000

27.3

12.3

14.3

30.7

10000

32.0

12.6

17.0

42.3

NTG

10

12.7

800

16.6

45.7

100

1000

2000

38.2

72.3

1000

2500

4000

84.1

140

Summary of results with metabolic activation

Strain

Chemical

Dose

(mg/ plate)

Revertant colonies/plate

Rat

Mouse

Liver

Lung

Kidney

Testis

Brain

Liver

TA1535

DMSO

10000

13.0

13.3

16.1

9.0

14.0

16.2

Fenitrothion

10

15.0

20.7

19.7

13.0

18.7

17.0

100

15.0

22.7

19.0

7.0

23.3

16.3

1000

16.3

17.0

20.7

11.3

21.3

15.7

2-AA

100

76.3

53.0

15.3

5.0

5.7

131

1000

138

62.3

15.7

7.3

7.0

170

TA1538

DMSO

10000

46.2

43.1

38.8

34.8

40.8

37.6

Fenitrothion

10

51.7

71.3

36.7

36.6

38.3

45.3

100

44.3

75.0

33.3

33.3

28.0

31.3

1000

40.3

56.7

34.7

34.7

27.3

24.0

2-AA

100

272

57.0

116

105

69.0

1000

1000

1500

101

161

38.3

46.6

1800

Conclusions:
Fenitrothion did not show any increase in the number of revertant colonies with or without metabolic activation in any of the strains investigated.
Executive summary:

The mutagenic potential of fenitrothion was investigated in a non-standard Ames test. Salmonella typhimurium strains TA1535, TA1537 and TA1538; and E. coli strain W3102 were exposed in triplicate to fenitrothion (dissolved in DMSO) at concentrations of 10, 100, 1000 or 10000 ug/plate in the absence or presence of metabolic activation (homogenates of liver, lung, kidney, testis and brain homogenate from male SD rats intraperitoneally injected with 3-methylcholanthrene (20 mg/kg) for 24 hr and liver homogenate from male ICR mice pretreated with 1% sodium phenobarbital in drinking water for one week). Fenitrothion did not show any increase in the number of revertant colonies with or without metabolic activation in any of the strains investigated. Positive control substances (2 -AA, NTG) showed marked increases in the numbers of revertant colonies. There is no evidence of mutagenicity in this study.

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

Genetic toxicity in vivo

Description of key information

Studies of micronucleus formation and clastogenicity in vivo are available for fenitrothion.

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
23 March 1982 - 14 April 1982
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
GLP compliance:
no
Type of assay:
mammalian erythrocyte micronucleus test
Specific details on test material used for the study:
Fenitrothion
Batch No.: 00106
Purity: 96.8%
Species:
mouse
Strain:
ICR
Details on species / strain selection:
Standard species/strain used for regulatory studies
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Shizuoka Agricultural Cooperative Association for Laboratory Animals (Japan)
- Age at study initiation: 7-8 weeks
- Weight at study initiation: 33-45 g
- Diet: ad libitum)
- Water: e.g. ad libitum
- Acclimation period: one week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23-25
- Humidity (%): 50-70
- Air changes (per hr): 16
- Photoperiod (hrs dark / hrs light): 12-12

IN-LIFE DATES: From: 23 March 1982 To: 14 April 1982
Route of administration:
intraperitoneal
Vehicle:
Corn oil
Details on exposure:
Groups of 6 male ICR mice (7 to 8 weeks old) each received a single intraperitoneal injection of fenitrothion in corn oil at dose levels of 200, 400, 800 and 1600 mg/kg bw (10 mL kg/bw)
Duration of treatment / exposure:
Single intraperitoneal injection
Frequency of treatment:
Single intraperitoneal injection
Post exposure period:
24 hours
Dose / conc.:
0 mg/kg bw/day
Remarks:
Vehicle (corn oil) control
Dose / conc.:
200 mg/kg bw/day
Remarks:
Single intraperitoneal injection
Dose / conc.:
400 mg/kg bw/day
Remarks:
Single intraperitoneal injection
Dose / conc.:
800 mg/kg bw/day
Remarks:
Single intraperitoneal injection
Dose / conc.:
1 600 mg/kg bw/day
Remarks:
Single intraperitoneal injection
No. of animals per sex per dose:
6 males
Control animals:
yes, concurrent vehicle
Positive control(s):
Mitomycin C, 4 mg/kg bw
Tissues and cell types examined:
Polychromatic bone marrow erythrocytes
Details of tissue and slide preparation:
Mice were sacrificed 24 hours after administration. Bone marrow cells were obtained from a femur, fixed, stained (Giemsa) and analyzed in a blind manner. A thousand erythrocytes were observed and the incidence of micronucleated cells as well as the ratio of polychromatic erythrocytes to whole erythrocytes were examined from each animal. The micronucleated cells in 1000 polychromatic erythrocytes were also counted
Evaluation criteria:
Not reported
Statistics:
The incidence of micronucleated cells was assessed according to Kastenbaum & Bowman; the t-test was used for assessment of the PCE:NCE ratio.
Key result
Sex:
male
Genotoxicity:
negative
Toxicity:
yes
Remarks:
Mortality at 1600 mg/kg bw; altered PCE ratio at 800 mg/kg bw
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
All mice administered 1600 mg/kg bw fenitrothion died before scheduled sacrifice.

Summary of findings

Treatment

Dose level (mg/kg bw)

Time

No. mice

No. cells

PCEs (%)

Micronucleated erythrocytes (%)

Micronucleated PCEs (%)

Corn oil

10 ml/kg

24h

6

6000

30.9

0.08

0.18

Fenitrothion

200

24h

6

6000

36.0

0.25*

0.25

400

24h

6

6000

36.8

0.10

0.17

800

24h

6

6000

44.4**

0.18

0.30

MMC

4

24h

6

6000

31.0

1.45**

4.75**

**significantly different to controls (p<0.01)

PCE: polychromatic erythrocyte

Conclusions:
Fenitrothion did not induce micronuclei in the bone marrow cells of mice under the conditions of this study.
Executive summary:

In a mouse bone marrow micronucleus assay, groups of 6 male ICR mice (7 to 8 weeks old) each received a single intraperitoneal injection of fenitrothion in corn oil at dose levels of 200, 400, 800 and 1600 mg/kg bw (10 mL/kg bw). All animals at 1600 mg/kg bw died before the scheduled sacrifice. Mice were sacrificed 24 hours after administration. Bone marrow cells were obtained from a femur, fixed, stained (Giemsa) and analysed in a blind manner. A thousand erythrocytes were observed and the incidence of micronucleated cells as well as the ratio of polychromatic erythrocytes to whole erythrocytes were examined from each animal. The micronucleated cells in 1000 polychromatic erythrocytes were also counted. Negative controls (corn oil) and positive controls (mitomycin C 4 mg/kg bw; 10 mL/kg bw) were similarly assessed. All mice administered 1600 mg/kg bw fenitrothion died before scheduled sacrifice. A significantly increased PCE ratio in mice at 800 mg/kg bw indicated adequate exposure of the target tissue. A statistically significant increase in the incidence of micronucleated PCEs was seen in the low dose group, but is not considered to be of biological relevance in the absence of similar findings in the other dose groups. The PCE ratio was significantly increased in the high dsoe group, indicating exposure of the target tissue. Fenitrothion did not induce micronuclei in the bone marrow cells of mice under the conditions of this study.

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
15 April 1982 - 25 May 1982
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)
GLP compliance:
no
Type of assay:
mammalian bone marrow chromosome aberration test
Specific details on test material used for the study:
Fenitrothion
Batch No.: 00106
Purity: 96.8%
Species:
mouse
Strain:
ICR
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Shizuoka Agricultural Coopertaive Association for Laboratory Animals
- Age at study initiation: 7-8 weeks
- Weight at study initiation: 33-45 g
- Housing:
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 1 week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23-25
- Humidity (%): 50-70
- Air changes (per hr): 16
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 15 April 1982 To: 25 May 1982
Route of administration:
intraperitoneal
Vehicle:
Corn oil
Details on exposure:
Groups of 6 male ICR mice (7 to 8 weeks old) each received a single intraperitoneal injection of fenitrothion, in corn oil at dose levels of 200, 400 and 800 mg/kg bw (10 mL/kg bw). Mice were injected with 4 mg/kg of colchicine 2 hours before sacrifice.
Duration of treatment / exposure:
Single intraperitoneal injection
Frequency of treatment:
Single injection
Post exposure period:
6, 24, 48 hours
Dose / conc.:
0 mg/kg bw/day (actual dose received)
Remarks:
Control (corn oil)
Dose / conc.:
200 mg/kg bw/day (actual dose received)
Remarks:
Single intraperitoneal injection
Dose / conc.:
400 mg/kg bw/day (actual dose received)
Remarks:
Single intraperitoneal injection
Dose / conc.:
800 mg/kg bw/day (actual dose received)
Remarks:
Single intraperitoneal injection
No. of animals per sex per dose:
6 males
Control animals:
yes, concurrent vehicle
Positive control(s):
Mitomycin C (4 mg/kg bw)
Tissues and cell types examined:
Bone marrow cells
Details of tissue and slide preparation:
Bone marrow cells were harvested, fixed, stained (Giemsa) and analyzed in a blind manner. Fifty well-spread metaphases from each animal were observed under microscope.
Evaluation criteria:
No details
Statistics:
Appropriate statistical methods (chi-squared test) were used to compare the control and test groups.
Key result
Sex:
male
Genotoxicity:
negative
Toxicity:
not specified
Remarks:
Toxicity not detailed, but predicted on the basis of the preliminary study
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid
Additional information on results:
In the fenitrothion treated groups, there was no significant increase in frequencies of chromosomal aberrations compared with the corresponding vehicle control value.

Summary of findings

 

Chemical

 

Dose

(mg/kgbw)

Time after injection

No. mice

No.

cells

Cells with aberration

(%)

No. of aberrations

G

B

E

m.a.

P

Corn oil

-b)

6

6

300

0.7

1

1

0

0

0

Fenitrothion

200

6

6

300

1.0

2

1

0

0

0

400

6

6

300

0.0

0

0

0

0

0

800

6

6

300

1.0

2

1

0

0

0

MMC

4

6

6

300

30.3**

27

25

94

5

0

Corn oil

-

24

6

300

1.7

4

1

0

0

0

Fenitrothion

200

24

6

300

0.0

0

0

0

0

0

400

24

6

300

0.0

0

0

0

0

0

800

24

6

300

0.7

2

0

0

0

0

MMC

4

24

6

300

66.3**

187

190

95

26

9

Corn oil

-

48

6

300

0.3

1

0

0

0

0

Fenitrothion

200

48

6

300

0.7

2

0

0

0

0

400

48

6

300

0.0

0

0

0

0

0

800

48

6

300

0.7

2

0

0

0

0

MMC

4

48

6

300

16.3**

11

2

19

11

18

G: gaps

B: breaks

E: exchanges

P: pulverised

m.a.: multiuple aberrations

**significantly different to controls (p<0.01)

Conclusions:
Fenitrothion did not induce chromosomal aberrations in bone marrow cells of mice under the conditions of this study.
Executive summary:

The potential of fenitrothion to cause chromosomal aberrations was investigated in a study in the mouse. Groups of 6 male ICR mice (7 to 8 weeks old) each received a single intraperitoneal injection of fenitrothion, in corn oil at dose levels of 200, 400 and 800 mg/kg bw. Mice were injected with 4 mg/kg bw of colchicine 2 hours before sacrifice. Bone marrow cells were harvested, fixed, stained (Giemsa) and analyzed in a blind manner. Fifty well-spread metaphases from each animal were observed under microscope. In the fenitrothion treated groups, there was no significant increase in frequencies of chromosomal aberrations compared with the corresponding vehicle control value.  The positive control (mitomycin C 4 mg/kg bw) produced significant increases in the proportion of cells with chromosomal aberrations. Fenitrothion did not induce chromosomal aberrations in bone marrow cells of mice under the conditions of this study.

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
9 September 1982 - 17 December 1982
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)
GLP compliance:
no
Type of assay:
mammalian bone marrow chromosome aberration test
Specific details on test material used for the study:
Fenitrothion
Batch No.: 00106
Purity: 96.8%
Species:
rat
Strain:
Sprague-Dawley
Details on species / strain selection:
Standard strain / species used in regulatory studies
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Japan
- Age at study initiation: 4-5 weeks
- Weight at study initiation: 80-160 g
- Diet :ad libitum
- Water: ad libitum
- Acclimation period: One week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23-25
- Humidity (%): 50-70
- Air changes (per hr): 16
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 9 September 1982 To: 17 December 1982
Route of administration:
oral: gavage
Vehicle:
Cottonseed oil
Details on exposure:
A preliminary acute toxicity test was conducted to determine the dose levels to be used in the chromosomal aberration test. Rats were treated with fenitrothion at dose levels of 400, 800, 1200 and 1600 mg/kg bw. In the chromosomal aberration test, dose levels of 100, 200, 400 mg//kg bw (single treatment) or 20, 40, 80 mg/kg bw (5 consecutive doses with a 24 hour interval) were used. Rats were injected with 4 mg/kg bw colchicine 2 hours before sacrifice.
Duration of treatment / exposure:
The study used single doses and also five repeated daily doses
Frequency of treatment:
The study used single doses and also five repeated daily doses
Post exposure period:
6, 24, 48 hours (single dose)
6 hours (repeated dose)
Dose / conc.:
0 mg/kg bw/day
Remarks:
Vehicle (cottonseed oil), single dose
Dose / conc.:
100 mg/kg bw/day
Remarks:
Single dose
Dose / conc.:
200 mg/kg bw/day
Remarks:
Single dose
Dose / conc.:
400 mg/kg bw/day
Remarks:
Single dose
Dose / conc.:
0 mg/kg bw/day
Remarks:
Vehicle (cottonseed oil): 5 consecutive daily doses
Dose / conc.:
20 mg/kg bw/day
Remarks:
5 consecutive daily doses
Dose / conc.:
40 mg/kg bw/day
Remarks:
5 consecutive daily doses
Dose / conc.:
80 mg/kg bw/day
Remarks:
5 consecutive daily doses
No. of animals per sex per dose:
6 males
Control animals:
yes, concurrent vehicle
Positive control(s):
Cyclophosphamide, 60 mg/kg bw
Tissues and cell types examined:
Bone marrow cells
Details of tissue and slide preparation:
Bone marrow cells were then harvested, fixed, stained (Giemsa) and analyzed in a blind manner. Fifty well-spread metaphases from each animal were observed under a microscope.
Evaluation criteria:
Not reported
Statistics:
Appropriate statistical methods (chi-squared test) were used to compare the control and treated groups.
Key result
Sex:
male
Genotoxicity:
negative
Toxicity:
not specified
Remarks:
Toxicity was not reported but can be predicted based on the results of the range-finding study
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid

Summary of findings

 

Chemical

 

Dose

(mg/kg bw)

Time

No. rats

No. cells

Cell with aberrations

(%)

No. of aberrations

G

B

E

m.a.

P

-control

-

6h

6

300

0.7

1

1

0

0

0

Fenitrothion

100

6h

6

300

1.0

2

1

0

0

0

200

6h

6

300

0.7

2

0

0

0

0

400

6h

6

300

1.3

4

0

0

0

0

+control

60

6h

6

300

22.0**

59

23

6

0

0

-control

-

24h

6

300

0.7

2

0

0

0

0

Fenitrothion

100

24h

6

300

0.7

2

0

0

0

0

200

24h

5c)

300

0.4

1

0

0

0

0

400

24h

6

300

1.3

4

0

0

0

0

+control

60

24h

6

300

44.7**

105

62

45

42

2

-control

-

48h

6

300

0.7

2

0

0

0

0

Fenitrothion

100

48h

6

300

0.0

0

0

0

0

0

200

48h

6

300

0.3

1

0

0

0

0

400

48h

6

300

1.0

1

2

0

0

0

CP

60

48h

6

300

1.0

1

2

4

0

0

-control

-

6h

6

300

0.3

1

0

0

0

0

Fenitrothion

20 x5

6h

6

300

1.0

2

1

0

0

0

40 x5

6h

6

300

0.3

0

1

0

0

0

80 x5

6h

6

300

1.0

2

1

0

0

0

**significantly different to controls (p<0.01)

G: gaps

B: breaks

E: exchanges

P: pulverisation

m.a.: multiple aberrations

Conclusions:
Fenitrothion did not induce chromosomal aberrations in bone marrow cells of rats, under the conditions of this study.
Executive summary:

The potential of fenitrothion to cause chromosomal aberrations was investigated in a study in the rat. A preliminary acute toxicity test was conducted to determine the dose levels to be used in the chromosomal aberration test. Rats were treated with fenitrothion at dose levels of 400, 800, 1200 and 1600 mg/kg bw.  In the chromosomal aberration test, dose levels of 100, 200, 400 mg//kg bw (single treatment) or 20, 40, 80 mg/kg bw (5 consecutive doses with a 24 hour interval) were used. Rats were injected with 4 mg/kg bw colchicine 2 hours before sacrifice. In fenitrothion treated groups, there was no significant increase in frequencies of chromosomal aberrations compared with the negative control values. The positive control (cyclophosphamide 60 mg/kg bw) produced significant amounts of chromosomal aberrations at 6 and 24 hours after administration. Fenitrothion did not induce chromosomal aberrations in bone marrow cells of rats, under the conditions of this study.

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

Mode of Action Analysis / Human Relevance Framework

A weakly positive response reported in S. typhiumurium TA100 was shown to be bacterial-specifc (nitroreductase-dependent) and is not considered to be relevant to humans.

Additional information

Studies in vitro

In the key Ames test, fenitrothion was tested using strains of Salmonella typhimurium (TA98, TA100, TA1535, TA1537, TA100 NR (nitroreductase-deficient strain) and TA100 1,8 -DNP6 (transacetylase-deficient strain)); andEscherichia coliWP2uvrA. Purified samples of fenitrothion and aminofenitrothion (AM-FNT) were tested using strains TA98, TA100, TA100 NR and TA100 1,8 -DNP6. Test chemicals were dissolved in DMSO and tests were conducted using a pre-incubation method with and without metabolic activation. Negative control (DMSO, 100 ul /plate), positive and insensitive controls were also tested with and without metabolic activation. S9 mix, a mixture of cofactors and the liver S9 from Sprague-Dawley rats treated intraperitoneally with polychlorinated biphenyls (PCB), were used for metabolic activation. Fenitrothion was found to be non-mutagenic in TA98, TA1535, TA1537 and WP2uvrA both with and without S9 mix, while weak mutagenicity was observed only in TA100 and it was enhanced by the addition of S9 mix. The mutagenicity was not observed in a nitroreductase-deficient strain, TA100 NR, and it decreased in a transacetylase-deficient strain, TA100 1,8-DNP6. The results suggest that the bacterial nitroreductase activity is necessary for fenitrothion to express the mutagenicity in TA100.

In a supporting Ames test, fenitrothion was investigated in Salmonella typhimurium strains TA1535, TA1537 and TA1538; and E. colis train W3102. Strains were exposed in triplicate to fenitrothion (dissolved in DMSO) at concentrations of 10, 100, 1000 or 10000 ug/plate in the absence or presence of metabolic activation (homogenates of liver, lung, kidney, testis and brain homogenate from male SD rats intraperitoneally injected with 3-methylcholanthrene (20 mg/kg) for 24 hr and liver homogenate from male ICR mice pretreated with 1% sodium phenobarbital in drinking water for one week). Fenitrothion did not show any increase in the number of revertant colonies with or without metabolic activation in any of the strains investigated. Positive control substances (2 -AA, NTG) showed marked increases in the numbers of revertant colonies. There is no evidence of mutagenicity in this study.

The potential clastogenicity of fenitrothion was investigated in CHO-K1 cells. A preliminary cytotoxicity test was performed to determine the concentrations to be used in the main study. The concentrations ranged from 1 -300 µg/mL with and without metabolic activation. In the chromosomal aberration test, Chinese hamster ovary cells (CHO-K1) were treated with fenitrothion (dissolved in DMSO) at concentrations of 3, 10 and 30 µg/mL for periods of 8, 16 or 24 hours in the absence of metabolic activation. In the presence of metabolic activation, cells were exposed to concentrations of 75, 150 and 300 µg/mL for 2 hours, with further culture in a fresh medium for 14 or 22 hours after removal of the test chemical. The cells were harvested, fixed, stained and analyzed in a blind manner. Negative control (DMSO) and positive controls (MMC, B(a)P, cyclophosphamide) were also tested. Mitotic indices were determined by counting more than 1000 cells. The number of structural aberrations and the frequencies of cells with structural aberrations were obtained by observation of 100 cells from each duplicate culture at each experimental point, and also the frequencies of polyploid cells were determined by observation of an additional 200 cells. Fenitrothion did not induce any significant increase in the number of total chromosome aberrations or in the frequency of cells with structural aberrations in the presence or absence of metabolic activation. A slight increase of the incidence of polyploid cells was observed in one culture of the 8 -hour treatment group at a concentration of 10 µg/ml in the absence of metabolic activation. However, no significant increase of polyploid cells was observed in other cultures and time- or concentration-dependency was not observed. Thus it was concluded that the increase was spontaneous. Positive control chemicals induced marked increases both in the number of total chromosome aberrations and in the frequency of cells with chromosomal aberrations. Fenitrothion does not have any clastogenic potential against CHO-K1 cells under the conditions tested.

The mutagenic potential of fenitrothion was investigated in an HPRT assay using V79 cells. To determine appropriate concentrations for use in the gene mutation test, a preliminary cytotoxicity test was performed using concentrations of 10e-3 to 10e-5 M with a dilution factor of 3 in the presence and absence of metabolic activation system (S9 mix). In the main study, cultures of V79 cells were treated with fenitrothion at concentrations of 10e-5 M, 3×10e-5 M, 10e-4 M and 3×10e-4 M with and without S9. Fenitrothion was dissolved in dimethyl sulphoxide (DMSO). Negative (sovent) controls (DMSO 1%) and positive controls (N-methyl-N’-nitro-N-nitrosoguanidine 3×10e-6 M; 9,10 -dimethyl-1,2 -benzanthracene 3×10e-5 M) were run concurrently. After incubation for five hours at 37°C, the cells were washed and cultured to determine cytotoxicity and to allow for expression of the mutant phenotype at 37°C for 7 days. After the expression period, the cells were innoculated to dishes with and without 6-thioguanine (6-TG) and cultivated for 6 or 7 days to determine the number of mutants and plating efficiency. Colonies formed were fixed, Giemsa-stained and counted. The number of colonies for each dish was counted and the mutation frequency and the plating efficiency were calculated. In the first experiment without metabolic activation, the mutation frequencies of the fenitrothion-treated groups were statistically significantly higher than that of the negative control group, but no concentration-dependent increase was observed. The result in the second experiment with two negative control groups showed no significant differences. In the first experiment with metabolic activation, the mutation frequencies of the fenitrothion-treated groups were partly higher than that of the negative control group, but no concentration-dependent increase was observed. In the second experiment, a small increase was observed at the highest concentration in the mutation frequency, but these values were within the range of historical control data. Small increases in the mutation frequencies are considered to be within the range of variation of the spontaneous mutation frequency, and no reproducible dose-response relationship were observed both in the presence and absence of metabolic activation. Fenitrothion was concluded not mutagenic under the test conditions.

Studies in vivo

In a mouse bone marrow micronucleus assay, groups of 6 male ICR mice (7 to 8 weeks old) each received a single intraperitoneal injection of fenitrothion in corn oil at dose levels of 200, 400, 800 and 1600 mg/kg bw (10 mL/kg bw). All animals at 1600 mg/kg bw died before the scheduled sacrifice. Mice were sacrificed 24 hours after administration. Bone marrow cells were obtained from a femur, fixed, stained (Giemsa) and analysed in a blind manner. A thousand erythrocytes were observed and the incidence of micronucleated cells as well as the ratio of polychromatic erythrocytes to whole erythrocytes were examined from each animal. The micronucleated cells in 1000 polychromatic erythrocytes were also counted. Negative controls (corn oil) and positive controls (mitomycin C 4 mg/kg bw; 10 mL/kg bw) were similarly assessed. All mice administered 1600 mg/kg bw fenitrothion died before scheduled sacrifice. A significantly increased PCE ratio in mice at 800 mg/kg bw indicated adequate exposure of the target tissue. A statistically significant increase in the incidence of micronucleated PCEs was seen in the low dose group, but is not considered to be of biological relevance in the absence of similar findings in the other dose groups. The PCE ratio was significantly increased in the high dsoe group, indicating exposure of the target tissue. Fenitrothion did not induce micronuclei in the bone marrow cells of mice under the conditions of this study.

The potential of fenitrothion to cause chromosomal aberrations was investigated in a study in the mouse. Groups of 6 male ICR mice (7 to 8 weeks old) each received a single intraperitoneal injection of fenitrothion, in corn oil at dose levels of 200, 400 and 800 mg/kg bw. Mice were injected with 4 mg/kg bw of colchicine 2 hours before sacrifice. Bone marrow cells were harvested, fixed, stained (Giemsa) and analyzed in a blind manner. Fifty well-spread metaphases from each animal were observed under microscope.In the fenitrothion treated groups, there was no significant increase in frequencies of chromosomal aberrations compared with the corresponding vehicle control value.  The positive control (mitomycin C 4 mg/kg bw) produced significant increases in the proportion of cells with chromosomal aberrations.Fenitrothion did not induce chromosomal aberrations in bone marrow cells of mice under the conditions of this study.

The potential of fenitrothion to cause chromosomal aberrations was investigated in a study in the rat. A preliminary acute toxicity test was conducted to determine the dose levels to be used in the chromosomal aberration test. Rats were treated with fenitrothion at dose levels of 400, 800, 1200 and 1600 mg/kg bw.  In the chromosomal aberration test, dose levels of 100, 200, 400 mg//kg bw (single treatment) or 20, 40, 80 mg/kg bw (5 consecutive doses with a 24 hour interval) were used. Rats were injected with 4 mg/kg bw colchicine 2 hours before sacrifice.In fenitrothion treated groups, there was no significant increase in frequencies of chromosomal aberrations compared with the negative control values. The positive control (cyclophosphamide 60 mg/kg bw) produced significant amounts of chromosomal aberrations at 6 and 24 hours after administration.Fenitrothion did not induce chromosomal aberrations in bone marrow cells of rats, under the conditions of this study.

Justification for classification or non-classification

Fenitrothion has a harmonised classification but is not classified for germ cell mutagenicity. In the absence of relevant findings in the available studies, no change to this classification is proposed.