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Toxicological information

Neurotoxicity

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Description of key information

An acute oral neurotoxicity study in the rat is available. A study of delayed neuropathy in the hen is available. A non-standard study of acute ocular toxicity is also available.

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Link to relevant study records

Referenceopen allclose all

Endpoint:
neurotoxicity: acute oral
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2 March 1992 - 20 March 1992
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EPA OPP 81-8 (Neurotoxicity Screening Battery)
GLP compliance:
yes
Limit test:
no
Specific details on test material used for the study:
Fenitrothion
Batch No.: 90617
Purity: 94.3%
Species:
rat
Strain:
Sprague-Dawley
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River, Canada
- Age at study initiation: 49-52 days
- Weight at study initiation: 227-285 g (M), 162-202 g (F)
- Housing: Individual
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-24
- Humidity (%): 30-70
- Air changes: 12-15/hour
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 2 ~March 1992 To: 20 March 1992
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
Groups of 12 or 13 male and 12 or 13 female Sprague-Dawley Crl:CD®(SD)BR rats received fenitrothion dissolved in corn oil, once by gavage at dose levels of 0, 12.5, 50 or 200 mg/kg bw for males and 0, 50, 200 or 800 mg/kg bw for females, at the dosage volume of 5 mL/kg bw.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Achieved concentrations, stability and homogeneith of the dosing solutions were verifed analytically
Duration of treatment / exposure:
Single gavage dose
Frequency of treatment:
Single gavage dose
Dose / conc.:
0 mg/kg bw/day
Remarks:
Vehicle control (corn oil): M, F
Dose / conc.:
12.5 mg/kg bw/day
Remarks:
M
Dose / conc.:
50 mg/kg bw/day
Remarks:
M, F
Dose / conc.:
200 mg/kg bw/day
Remarks:
M, F
Dose / conc.:
800 mg/kg bw/day
Remarks:
F
No. of animals per sex per dose:
12 or 13
Control animals:
yes, concurrent vehicle
Details on study design:
The animals were evaluated using a functional observation battery (FOB) and motor activity test on prestudy, days 0 (day of treatment, at the time of peak effect), 7 and 14. At the completion of the study (day 15), 6 animals/sex/group were randomly selected for perfusion and those in the control and high dose groups underwent a neuropathological evaluation. The remaining animals in each group had their brains removed and then were subjected to necropsy. The brain of each of these rats in the control, low dose and high dose groups was subsequently analyzed for glial fibrillary acidic protein (GFAP) content.
Observations and clinical examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily

BODY WEIGHT: Yes
- Time schedule for examinations: Days 0, 7, 14, 15
Neurobehavioural examinations performed and frequency:
The animals were evaluated using a functional observation battery (FOB) and motor activity test on prestudy, days 0 (day of treatment, at the time of peak effect), 7 and 14.
Sacrifice and (histo)pathology:
At the completion of the study (day 15), 6 animals/sex/group were randomly selected for perfusion and those in the control and high dose groups underwent a neuropathological evaluation. The remaining animals in each group had their brains removed and then were subjected to necropsy. The brain of each of these rats in the control, low dose and high dose groups was subsequently analyzed for glial fibrillary acidic protein (GFAP) content.
Positive control:
Not required
Statistics:
Diffferences between the control and treated groups were assessed using appropriate statistical methods
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
On the first few days following treatment, several abnormal clinical findings were observed such as wet fur staining along the ventral surface for the 200 and 800 mg/kg bw group rats and ocular discharge for the 200 mg/kg bw group males and one female from this same group, and for 800 mg/kg bw group females. For several male rats in the 200 mg/kg bw group, one female from this same group, and for most 800 mg/kg bw females, the tremors persisted for a few days post dosing. A few 800 mg/kg bw group females also appeared dehydrated or had a prominent backbone. Aside from some occasional dry fur staining, no abnormal findings were evident beyond Day 4.
Dermal irritation (if dermal study):
not examined
Mortality:
mortality observed, treatment-related
Description (incidence):
One female in the 800 mg/kg bw group and one male in the 200 mg/kg bw group were found dead on Days 1 and 2, respectively.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
The 200 mg/kg bw males had a significant decrease in body weights on all occasions following treatment compared to the control group
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
effects observed, treatment-related
Description (incidence and severity):
The FOB performed on Day 0 found several significant differences between control and fenitrothion-treated groups, including tremors, gait incapacity, reduced locomotor activity levels and arousal, decreased rearing and reduced body temperature for 50 and 200 mg/kg bw males and females and 800 mg/kg bw females. Autonomic signs such as myosis and salivation, together with a reduced response to pain perception (toe and tail pinch tests), abnormal visual placing response, and delays for the positional passivity test and failed air righting reflex were also observed for the 50 mg/kg bw males, 200 mg/kg bw males and females, and 800 mg/kg bw females. An abnormal home cage body position observed as lying down on ventral surface also occurred for males in the 50 mg/kg bw and 200 mg/kg bw groups and for females in the 800 mg/kg bw group. In addition, quantitative measurements of limb strength showed reductions in the forelimb for 50 and 200 mg/kg bw males and 800 mg/kg bw females, and decreases in the hindlimb for 200 mg/kg bw males and females and 800 mg/kg bw females .
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
no effects observed
Neuropathological findings:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Histopathological findings: neoplastic:
no effects observed
Other effects:
effects observed, treatment-related
Description (incidence and severity):
Glial fibrillary acidic protein content in the cerebral cortex of the 800 mg/kg group females was significantly elevated. The biological significance of this finding remains unclear given the variability of the data in both control and fenitrothion-treated groups, the increase in group mean was in part attributable to one rat with a high value, and that no structural changes in the nervous system were seen .
Details on results:
Measurements on Day 0 indicated significant reductions in total activity counts for 50 and 200 mg/kg bw males, and 50, 200 and 800 mg/kg bw females. The linear constructed variable was similarly affected for the females. In addition, trend analysis on female data found a significant linear and quadratic dose level effect for total activity counts and the linear constructed variable. No significant differences were detected between the control and 12.5 mg/kg bw males.
Key result
Dose descriptor:
NOAEL
Effect level:
12.5 mg/kg bw/day
Based on:
test mat.
Sex:
male
Basis for effect level:
behaviour (functional findings)
Key result
Dose descriptor:
LOAEL
Effect level:
50 mg/kg bw/day
Based on:
test mat.
Sex:
female
Basis for effect level:
behaviour (functional findings)
Key result
Critical effects observed:
yes
Lowest effective dose / conc.:
50 mg/kg bw/day
System:
central nervous system
Organ:
brain
Treatment related:
yes
Dose response relationship:
yes
Relevant for humans:
yes

Summary of bodyweights

Dose level (mg/kg bw)

M

F

0

12.5

50

200

0

50

200

800

Day 0

261.8

261.0

262.2

262.6

180.5

178.0

179.9

181.9

Day 7

307.5

309.4

297.3

282.9**

200.4

190.4

194.2

189.2

Day 14

345.8

349.2

335.6

328.3*

217.4

208.1

211.2

212.1

Day 15

310.9

312.9

300.5

293.9*

195.1

187.0

187.9

189.3

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

Clinical findings

Male

 

 

 

 

Dose level

0 mg/kg bw

12.5 mg/kg bw

50 mg/kg bw

200 mg/kg bw

Number of animals examined

13

13

13

12

Behavior - slight fine tremors

0

0

0

6

Eyes - dry red discharge

0

0

0

11

Fur - urogenital region - yellow staining

0

0

3

12

Fur - abdominal region - yellow staining

0

0

0

9

Female

 

 

 

 

Dose level

0 mg/kg

50 mg/kg

200 mg/kg

800 mg/kg

Number of animals examined

13

12

12

12

Dehydrated/prominent backbone

0

0

0

8

Behavior - slight fine tremors

0

0

1

7

Eye - red discharge

0

0

1

7

Fur - urogenital region - yellow staining

0

0

4

11

Fur - abdominal region - yellow staining

0

0

0

7

Summary of FOB (Day 0, M)

Dose level

0 mg/kg bw

12.5 mg/kg bw

50 mg/kg bw

200 mg/kg bw

Number of animals examined

13

13

13

12

Body position (description)

 

 

 

 

Lying down ventral surface

0

0

6*

10***

Sitting/standing

10

12

7

2**

Rearing

3

1

0

0

Tremors (head, body and/or limbs) (description)

 

 

 

None

13

13

1***

0***

Slight fine

0

0

1***

0***

Slight coarse

0

0

7***

4***

Moderate coarse

0

0

4***

7***

Severe coarse

0

0

0***

1***

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

12.5 mg/kg bw

50 mg/kg bw

200 mg/kg bw

Number of animals examined

13

13

13

12

Rearing (mean score)

6.2

4.9

0.4***

0.0***

Ataxic gait (description)

 

 

 

 

Not recorded

0

0

4

11

None

13

13

1***

0

Slight

0

0

1***

0

Moderate

0

0

5***

0

Severe

0

0

2***

1

Overall gait incapacity (description)

 

 

 

 

None

13

13

1***

0***

Slight

0

0

2***

0***

Moderate

0

0

5***

0***

Severe

0

0

1***

1***

Extreme

0

0

4***

11***

Tremors (head, body and/or limbs) (description)

 

 

 

None

13

13

1***

0***

Slight fine

0

0

1***

0***

Slight coarse

0

0

7***

3***

Moderate coarse

0

0

4***

8***

Severe coarse

0

0

0***

1***

Locomotor activity level (description)

 

 

 

None resting

0

0

4***

11***

Slight movement

1

1

9***

1***

Moderate movement

12

12

0***

0***

Arousal (description)

 

 

 

Severely decreased

0

0

5***

11***

Moderately decreased

0

0

7***

1***

Normal

13

13

1***

0***

Defecation (mean score)

1.3

1.8

0.4

0.1**

Urination (description)

 

 

 

None

3

4

8

10**

Slight

10

9

5

2**

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

12.5 mg/kg bw

50 mg/kg bw

200 mg/kg bw

Number of animals examined

13

13

13

12

Pupil size (description)

 

 

 

 

Pinpoint

1

0

11***

12***

Pinhead

12

13

2***

0***

Exophthalmos

0

0

0

1

Salivation (description)

 

 

 

 

None

13

12

7*

1***

Slight

0

0

4*

2***

Moderate

0

0

2*

6***

Severe

0

0

0*

3***

Red coloration

0

0

2

4*

Extensor thrust (description)

 

 

 

 

Normal

13

13

11

3***

Slight reduction

0

0

2

8***

Moderate reduction

0

0

0

1***

Pinna reflex (description)

 

 

 

 

None

0

0

2*

5***

Slight brisk flick

0

0

4*

5***

Moderate brisk flick

12

13

7*

2***

Very brisk flick

1

0

0*

0***

Toe pinch (description)

 

 

 

 

No response

0

0

2**

10***

Slight withdrawal

1

0

8**

2***

Moderate withdrawal

10

13

3**

0***

Rapid withdrawal

2

0

0**

0***

Tail pinch (description)

 

 

 

 

No response

0

0

5***

12***

Slight movement

1

0

5***

0***

Moderate movement

11

13

3***

0***

Rapid movement

1

0

0***

0***

Visual placing (description)

 

 

 

 

No response

0

0

1***

8***

Nose touch

0

0

4***

4***

Vibrissae touch

0

0

6***

0***

Normal

13

13

2***

0***

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

12.5 mg/kg bw

50 mg/kg bw

200 mg/kg bw

Number of animals examined

13

13

13

12

Positional passivity (description)

 

 

 

 

Normal

13

13

5**

0***

Slight delay

0

0

4**

1***

Moderate delay

0

0

2**

1***

Severe delay

0

0

0**

1***

Cataleptic

0

0

2**

9***

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

50 mg/kg bw

200 mg/kg bw

800 mg/kg bw

Number of animals examined

13

12

12

12

Body position (description)

 

 

 

 

Lying down ventral surface

0

0

2

6**

Sitting/standing

13

12

10

6**

Tremors (head, body and/or limbs) (description)

 

 

 

None

13

8*

1***

0***

Slight fine

0

4*

6***

5***

Slight coarse

0

0*

5***

7***

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Summary of FOB findings (Day 0, F)

Dose level

0 mg/kg bw

50 mg/kg bw

200 mg/kg bw

800 mg/kg bw

Number of animals examined

13

12

12

12

Rearing (mean score)

10.9

3.1***

1.2***

0.6***

Ataxic gait (description)

 

 

 

 

Not recorded

0

0

0

4

None

13

4***

1***

0***

Slight

0

7***

2***

1***

Moderate

0

1***

8***

6***

Severe

0

0***

1***

1***

Overall gait incapacity (description)

 

 

 

 

None

13

4***

1***

0***

Slight

0

8***

6***

2***

Moderate

0

0***

4***

5***

Severe

0

0***

1***

1***

Extreme

0

0***

0***

4***

Tremors (head, body and/or limbs) (description)

 

 

 

None

13

8*

1***

0***

Slight fine

0

4*

6***

5***

Slight coarse

0

0*

5***

7***

Locomotor activity level (description)

 

 

 

None resting

0

0**

0***

4***

Slight movement

0

6**

11***

8***

Moderate movement

13

6**

1***

0***

Arousal (description)

 

 

 

Severely decreased

0

0*

1***

6***

Moderately decreased

0

4*

10***

6***

Normal

13

8*

1***

0***

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

50 mg/kg bw

200 mg/kg bw

800 mg/kg bw

Number of animals examined

13

12

12

12

Pupil size (description)

 

 

 

 

Pinpoint

0

1

4*

5*

Pinhead

13

11

8*

7*

Salivation (description)

 

 

 

 

Normal

13

12

8*

1***

Slight

0

0

2*

6***

Moderate

0

0

2*

3***

Severe

0

0

0*

2***

Pinna reflex (description)

 

 

 

 

None

0

0

0

2**

Slight brisk flick

0

0

2

4**

Moderate brisk flick

13

12

10

6**

Toe pinch (description)

 

 

 

 

No response

0

0

2**

3***

Slight withdrawal

0

1

4**

6***

Moderate withdrawal

13

11

6**

3***

Tail pinch (description)

 

 

 

 

No response

0

0

3**

5***

Slight movement

0

0

4**

5***

Moderate movement

13

12

5**

2***

Visual placing (description)

 

 

 

 

No response

0

0

1**

1***

Nose touch

0

0

1**

3***

Vibrissae touch

0

0

4**

4***

Normal

13

12

6**

4***

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

50 mg/kg bw

200 mg/kg bw

800 mg/kg bw

Number of animals examined

13

12

12

12

Positional passivity (description)

 

 

 

 

Normal

13

12

8*

5**

Slight delay

0

0

2*

2**

Moderate delay

0

0

1*

3**

Severe delay

0

0

1*

0**

Cataleptic

0

0

0*

2**

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Dose level

0 mg/kg bw

50 mg/kg bw

200 mg/kg bw

800 mg/kg bw

Number of animals examined

13

12

12

12

Air righting reflex (description)

 

 

 

 

Normal

13

12

7*

5**

Fails lands on side

0

0

3*

6**

Fails lands on back

0

0

2*

1**

Grip strength (Day 0)

 

Male

Female

Dose level (mg/kg bw)

0

12.5

50

200

0

50

200

800

Forelimb grip strength (g)

830.0

763.5

714.6*

428.3**

734.6

741.3

667.5

620.4*

Hindlimb grip strength (g)

668.8

620.4

602.3

470.8**

638.5

640.8

561.7*

544.6**

Body temperature (ºC)

37.7

37.7

34.1**

33.4**

38.1

36.0**

34.3**

33.4**

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

Motor activity (Day 0)

 

Male

Female

Dose level (mg/kg bw)

0

12.5

50

200

0

50

200

800

Day 0

176.3

176.1

28.4***

26.6***

355.5

99.8***

78.3***

46.3***

Day 7

213.7

208.4

236.0

259.2

349.1

362.2

320.9

275.5

Day 14

232.2

249.8

227.0

217.2

352.2

392.7

358.3

307.8

*significantly different to controls (p<0.05); **<0.01; ***p<0.001

GFAP in brain (relative to controls)

 

Male

Female

Dose level (mg/kg bw)

12.5

200

50

800

Cerebellum

95.5

108.2

107.5

101.3

Cerebral cortex

87.3

96.3

110.6

119.4*

Hippocampus

96.0

109.3

108.3

106.8

Striatum

103.5

110.1

92.7

104.9

Thalamus/hypothalamus

99.4

99.0

103.0

93.2

Remaining brain

97.3

106.0

100.3

100.8

*significantly different to controls (p<0.05)

Conclusions:
A NOAEL of 12.5 mg/kg bw was determined for males based on signs in the qualitative clinical and functional observation, reduction in grip strength, body temperature and motor activity at 50 mg/kg bw. A NOAEL was not demonstrated for females.
Executive summary:

The acute oral neurotoxicity of fenitrothion was investigated in the rat. Groups of 12 or 13 male and 12 or 13 female Sprague-Dawley Crl:CD®(SD)BR rats received fenitrothion dissolved in corn oil, once by gavage at dose levels of 0, 12.5, 50 or 200 mg/kg bw for males and 0, 50, 200 or 800 mg/kg bw for females, at the dosage volume of 5 mL/kg bw. The animals were evaluated using a functional observation battery (FOB) and motor activity test on prestudy, days 0 (day of treatment, at the time of peak effect), 7 and 14. At the completion of the study (day 15), 6 animals/sex/group were randomly selected for perfusion and those in the control and high dose groups underwent a neuropathological evaluation. The remaining animals in each group had their brains removed and then were subjected to necropsy. The brain of each of these rats in the control, low dose and high dose groups was subsequently analyzed for glial fibrillary acidic protein (GFAP) content. One female in the 800 mg/kg bw group and one male in the 200 mg/kg bw group were found dead on Days 1 and 2, respectively. On the first few days following treatment, several abnormal clinical findings were observed such as wet fur staining along the ventral surface for the 200 and 800 mg/kg bw group rats and ocular discharge for the 200 mg/kg bw group males and one female from this same group, and for 800 mg/kg bw group females. For several male rats in the 200 mg/kg bw group, one female from this same group, and for most 800 mg/kg bw group females, the tremors persisted for a few days post dosing. A few 800 mg/kg bw group females also appeared dehydrated or had a prominent backbone. Aside from some occasional dry fur staining, no abnormal findings were evident beyond Day 4. The 200 mg/kg bw males had a significant decrease in body weights on all occasions following treatment compared to the control group.  The FOB performed on Day 0 found several significant differences between control and fenitrothion-treated groups, including tremors, gait incapacity, reduced locomotor activity levels and arousal, decreased rearing and reduced body temperature for 50 and 200 mg/kg bw males and females and 800 mg/kg bw females. Autonomic signs such as myosis and salivation, together with a reduced response to pain perception (toe and tail pinch tests), abnormal visual placing response, and delays for the positional passivity test and failed air righting reflex were also observed for the 50 mg/kg bw males, 200 mg/kg bw males and females, and 800 mg/kg bw females. An abnormal home cage body position observed as lying down on ventral surface also occurred for males in the 50 mg/kg bw and 200 mg/kg bw groups and for females in the 800 mg/kg bw group. In addition, quantitative measurements of limb strength showed reductions in the forelimb for 50 and 200 mg/kg bw males and 800 mg/kg bw females, and decreases in the hindlimb for 200 mg/kg bw males and females and 800 mg/kg bw females. Measurements on Day 0 indicated significant reductions in total activity counts for 50 and 200 mg/kg bw males, and 50, 200 and 800 mg/kg bw females. The linear constructed variable was similarly affected for the females. In addition, trend analysis on female data found a significant linear and quadratic dose level effect for total activity counts and the linear constructed variable. No significant differences were detected between the control and 12.5 mg/kg bw males. Gross necropsy did not reveal any effects of treatment; there was no treatment-related neuropathology. Glial fibrillary acidic protein content in the cerebral cortex of the 800 mg/kg group females was significantly elevated. The biological significance of this finding remains unclear given the variability of the data in both control and fenitrothion-treated groups, the increase in group mean was in part attributable to one rat with a high value, and that no structural changes in the nervous system were seen. A NOAEL of 12.5 mg/kg bw was determined for males based on signs in the qualitative clinical and functional observation, reduction in grip strength, body temperature and motor activity at 50 mg/kg bw. A NOAEL was not demonstrated for females.

Endpoint:
neurotoxicity: acute oral
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
26 May 26 1988 - 26 August 1988
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline available
Principles of method if other than guideline:
Assessment of ocular toxicity following a single oral dose
GLP compliance:
no
Limit test:
no
Specific details on test material used for the study:
Fenitrothion
Batch No.: 60553
Purity: 94.5%
Species:
rat
Strain:
Sprague-Dawley
Remarks:
Crj:CD(SD)
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River, Japan
- Age at study initiation: 6-7 weeks
- Weight at study initiation: 162-213 g (M), 131-210 g (F)
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 14-21 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23-27
- Humidity (%): 52-77
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 10/14

IN-LIFE DATES: From: 26 May 1988 To: 26 August 1988
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
Groups of 25 male or 25 female Crj:CD(SD) rats received fenitrothion by single gastric intubation at the dose levels of 0, 20, 200 mg/kg bw for males and 0, 40, 400 mg/kg bw for females, dissolved in corn oil at a dose volume of 5 ml/kg bw.
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
Single gavage dose
Frequency of treatment:
Single gavage dose
Dose / conc.:
0 mg/kg bw/day
Remarks:
Vehicle (corn oil) control; M, F
Dose / conc.:
20 mg/kg bw/day
Remarks:
M
Dose / conc.:
40 mg/kg bw/day
Remarks:
F
Dose / conc.:
200 mg/kg bw/day
Remarks:
M
Dose / conc.:
400 mg/kg bw/day
Remarks:
F
No. of animals per sex per dose:
25
Control animals:
yes, concurrent vehicle
Details on study design:
Clinical signs and body weights were recorded for all animals. Ophthalmology and ERG examination, and autopsy on the eyes and their accessory organs were performed at 4, 7, 14, 28 and 91 days after dosing (5 animals/sex/group). Measurement of cholinesterase activity was performed on the next day of the ERG examination.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
Increased incidences of cholinergic symptoms such as muscular fibrillation, eye discharge, and salivation were observed in the high dose treatment groups of both sexes (200 mg/kg bw in males; 400 mg/kg bw in females). Increased incidences of muscular fibrillation were also noted in males at 20 mg/kg bw and females at 40 mg/kg bw.
Dermal irritation (if dermal study):
not examined
Mortality:
mortality observed, treatment-related
Description (incidence):
One male dose with 200 mg/kg bw died on hour following dosing.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
A significant, but transient, decrease in body weight was observed after the dosing in the high dose treatment groups of both sexes.
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
effects observed, non-treatment-related
Description (incidence and severity):
There were no significant differences between the treated groups and the control.
Haematological findings:
not examined
Clinical biochemistry findings:
effects observed, treatment-related
Description (incidence and severity):
Inhibition of cholinesterase activity in erythrocytes were observed in all treatment groups and marked inhibitions were noted in the high dose groups of both sexes from 5-15 days after dosing. Significant inhibition of cholinesterase activity in plasma was seen in females of the high dose group at 5 days after dosing. Enzyme activities gradually recovered thereafter and had fully recovered at 13 weeks after the dosing
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not examined
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
no effects observed
Histopathological findings: neoplastic:
not examined
Other effects:
no effects observed
Description (incidence and severity):
ERG examination showed some significant changes mainly in the high dose treatment groups. However, these changes were considered to be incidental, since their values were within normal range.
Key result
Dose descriptor:
NOAEL
Remarks on result:
not determinable
Key result
Critical effects observed:
yes
Lowest effective dose / conc.:
20 mg/kg bw/day
System:
peripheral nervous system
Organ:
neurons
Treatment related:
yes
Dose response relationship:
yes
Relevant for humans:
yes

Summary of clinical signs

 

Male

Female

Dose level (mg/kg bw)

0

20

200

0

40

400

Group A (observed for 4 days after the dosing)

 

 

 

 

 

Number of animals examined

5

5

5

5

5

5

Muscular fibrillation

0

3

4*

0

0

5**

Eye discharge

0

0

4*

0

0

2

Salivation

0

0

3

0

0

2

Group B (observed for 7 days after the dosing)

 

 

 

 

 

Number of animals examined

5

5

5

5

5

5

Muscular fibrillation

0

5**

5**

0

1

5**

Eye discharge

0

2

5**

0

0

0

Salivation

0

0

3

0

0

0

Group C (observed for 14 days after the dosing)

 

 

 

 

 

Number of animals examined

5

5

5

5

5

5

Muscular fibrillation

0

5**

5**

0

2

5**

Eye discharge

0

1

5**

0

0

1

Salivation

0

0

0

0

0

1

Group D (observed for 28 days after the dosing)

 

 

 

 

 

Number of animals examined

5

5

5

5

5

5

Muscular fibrillation

0

5**

5**

0

2

5**

Eye discharge

0

0

5**

0

0

4*

Salivation

0

0

4*

0

0

2

Group E (observed for 91 days after the dosing)

 

 

 

 

 

Number of animals examined

5

5

5

5

5

5

Muscular fibrillation

0

4*

5**

0

0

5**

Eye discharge

0

0

5**

0

0

4*

Salivation

0

0

5**

0

0

1

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

Summary of bodyweight effects

 

Male

Female

Dose level (mg/kg bw)

0

20

200

0

40

400

Group A (observed for 4 days after the dosing)

 

 

 

 

Day 0

167

175*

182**

138

140

136

Day 4

219

228

204

171

168

153*

Group B (observed for 7 days after the dosing)

 

 

 

 

Day 0

198

202

201

182

182

174

Day 4

248

248

220**

212

212

185*

Day 7

274

276

251**

219

226

200

Group C (observed for 14 days after the dosing)

 

 

 

 

Day 0

194

198

197

175

168

172

Day 4

244

243

217**

207

194

182**

Day 7

272

272

249*

217

204

198*

Day 14

334

330

316

236

230

232

Group D (observed for 28 days after the dosing)

 

 

 

 

Day 0

199

205

196

172

178

171

Day 4

247

254

213**

201

211

185

Day 7

273

284

243**

214

222

198

Day 14

330

344

307*

240

255

227

Day 21

363

393*

361

259

277

246

Day 28

402

439*

409

279

298

267

Group E (observed for 91 days after the dosing)

 

 

 

 

Day 0

191

184

187

164

162

154

Day 4

237

223

206**

199

193

162**

Day 7

266

249

238*

213

211

186**

Day 14

322

303

301

241

238

223

Day 21

370

350

357

262

263

256

Day 28

407

391

398

280

285

277

Day 35

442

420

426

299

300

300

Day 42

460

446

461

310

308

312

Day 49

486

468

487

321

317

325

Day 56

503

477

498

326

321

336

Day 63

516

494

517

336

328

345

Day 70

538

511

534

340

331

355

Day 77

549

521

544

347

343

364

Day 84

564

539

565

352

347

370

Day 91

579

549

581

358

354

380

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

Summary of electroretinogram findings

 

Male

Female

Dose level (mg/kg)

0

20

200

0

40

400

Peak latency time of a-wave (msec)

Day 4

17.7

16.3

16.6

16.5

17.8

17.3

Day 7

16.8

16.2

17.5

17.8

16.9

17.4

Day 14

17.4

18.0

16.4

15.2

16.3

15.3

Day 28

18.5

20.6

18.9

17.3

20.1**

18.7

Day 91

15.7

17.4

17.8

18.1

16.6

16.8

Amplitude of a-wave (mV)

Day 4

355

337

287

305

237

210

Day 7

240

242

327*

215

245

255

Day 14

267

230

300

380

345

250

Day 28

243

235

240

255

182**

245

Day 91

250

267

265

285

315

262

Peak latency time of b-wave (msec)

Day 4

63.0

61.4

57.6

60.5

61.3

60.6

Day 7

63.3

62.3

60.6

64.2

63.0

58.6*

Day 14

59.4

64.1

60.8

57.6

64.2

59.6

Day 28

60.4

60.2

59.3

60.8

61.1

62.5

Day 91

55.8

58.0

58.6

55.0

54.9

58.6

Amplitude of b-wave (mV)

Day 4

963

900

871

755

682

620

Day 7

712

640

860

620

652

710

Day 14

737

727

791

940

950

666

Day 28

537

735

755

742

627

727

Day 91

777

833

830

948

1031

887

1st peak latency time of oscillatory potentials (msec)

Day 4

33.2

28.8

29.3

32.5

33.7

31.8

Day 7

35.1

35.8

33.6

34.0

32.1

31.9

Day 14

31.4

31.7

30.5

30.6

31.7

29.4

Day 28

31.0

30.1

30.6

33.5

32.2

32.3

Day 91

28.7

29.0

29.9

29.0

28.0

31.1*

2nd peak latency time of oscillatory potentials (msec)

Day 4

41.1

36.0

37.0

40.9

41.0

40.6

Day 7

45.0

44.3

41.8

43.3

40.8

40.2

Day 14

39.2

38.8

38.4

38.2

39.2

38.6

Day 28

39.0

37.7

37.8

42.2

40.7

40.9

Day 91

35.9

36.3

36.8

36.4

35.1

38.4

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

Summary of cholinesterase activity

 

Male

Female

Dose level (mg/kg)

0

20

200

0

40

400

Plasma

 

 

 

 

 

 

Day 5

0.20

0.17

0.18

0.90

0.64

0.40**

Day 8

0.24

0.23

0.34

0.75

0.57

0.59

Day 15

0.23

0.19

0.24

0.98

0.99

0.79

Day 29

0.19

0.21

0.22

1.05

1.05

1.52

Day 92

0.14

0.20

0.19

1.67

1.58

1.44

Red blood cell

 

 

 

 

 

 

Day 5

0.35

0.22*

0.08**

0.29

0.17**

0.04**

Day 8

0.33

0.24**

0.09**

0.27

0.14

0.10**

Day 15

0.37

0.32

0.16**

0.37

0.26**

0.19**

Day 29

0.47

0.49

0.36

0.46

0.41

0.35

Day 92

0.41

0.42

0.39

0.38

0.34

0.36

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

Conclusions:
No acute ocular toxicity was detected in the rats given sub-lethal doses of fenitrothion which induced a remarkable inhibition of the cholinesterase activity and toxic signs.
Executive summary:

A non-standard study was performed to investigate the ocular toxicity of fenitrothion. Groups of SD rats (25/sex) were administered a single gavage dose of fenitrothion (in corn oil) at dose levels of 0, 20 or 200 mg/kg bw (males); 0, 40 or 400 mg/kg bw (females) and observed for up to 90 days. Signs of toxicity were observed and bodyweights measured. Opthalmology, histopathology of the eyes and ERG were performed at 4, 7, 14, 28 and 91 days after dosing. Cholinesterase activity was also measured. One mortality occurred in high dose males one hour following dosing. Signs of toxicity consistent with cholinesterase inhibition were observed in all treated groups. Inhibition of erythrocyte cholinesterase activity was shown in all treated groups. No acute ocular toxicity was detected in the rats given sub-lethal doses of fenitrothion which induced a remarkable inhibition of the cholinesterase activity and toxic signs.

Endpoint:
neurotoxicity: short-term oral
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
10 November 10 - 20 August 1976
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Assessment of delayed neurotoxicity in the hen follwoing single and repeated dosing
GLP compliance:
no
Limit test:
no
Species:
hen
Strain:
other: White Leghorn
Sex:
not specified
Route of administration:
oral: gavage
Vehicle:
other: 10% Tween 80 or Sorpol emulsifier
Details on exposure:
One group of 16 adult White Leghorn hens received fenitrothion dissolved in emulsifier (Sorpol 355), twice at the interval of 3-week at the dose level of 500 mg/kg, and then were kept under observation for 3 weeks after the second administration. Groups of 8 adult White Leghorn hens received fenitrothion suspended in 10% Tween 80 aqueous solution, by oral gavage for consecutive 4 weeks at the dose levels of 16.7 and 33.4 mg/kg, and then were kept under observation for 3 weeks after the 4-week administration period. As a positive control group, 3 adult White Leghorn hens received singly 500 mg/kg of tri-ortho-cresyl phosphate (TOCP), and were kept under observation for 4 weeks.
Analytical verification of doses or concentrations:
not specified
Duration of treatment / exposure:
One group of hens was administered two single doses of fenitrothion at a three week interval. Another group of hens was administered fenitrothion daily for 28 days.
Frequency of treatment:
One group of hens was administered two single doses of fenitrothion at a three week interval. Another group of hens was administered fenitrothion daily for 28 days.
Dose / conc.:
500 mg/kg bw/day (nominal)
Remarks:
Two doses at a 3-week interval
Dose / conc.:
16.7 mg/kg bw/day
Remarks:
Daily for 28 days
Dose / conc.:
33.4 mg/kg bw/day
Remarks:
Daily for 28 days
No. of animals per sex per dose:
16 (single dose); 8 (repeated dose)
Control animals:
not specified
Details on study design:
As a positive control group, 3 adult White Leghorn hens received singly 500 mg/kg of tri-ortho-cresyl phosphate (TOCP), and were kept under observation for 4 weeks. Paralysis in legs was checked daily, using a scoring system. Body weights were measured weekly. All surviving hens were sacrificed and sciatic nerves and spinal cords were dissected out and examined histopathologically.
Neurobehavioural examinations performed and frequency:
Paralysis in legs was checked daily, using a scoring system.
Sacrifice and (histo)pathology:
All surviving hens were sacrificed and sciatic nerves and spinal cords were dissected out and examined histopathologically.
Positive control:
TOCP (500 mg/kg bw), single dose
Statistics:
No details
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
In the acute study, signs including leg weakness, lack of leg coordination, loss of balance, decrease of spontaneous motor activity and irregular respiration were observed. The symptoms of acute intoxication disappeared 5-7 days post-treatment and no further noteworthy changes were observed.


In the repeated dose study, signs included decreased spontaneous motor activity, tremor and leg weakness as well as loss of appetite; signs gradually resolved. Paralysis in the legs was not observed.
Dermal irritation (if dermal study):
not examined
Mortality:
mortality observed, treatment-related
Description (incidence):
In the acute study, five out of sixteen hens died after 24-48 hours, regardless of atropine and 2-PAM treatment.

In the repeated dose study, one hen died on Day 5.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
In the acute study, bodyweights were lower at 1 week after administration and recovered slowly.

In the repeated dose study, mean body weights showed a slight decrease seven days after initiation of the administration and remained depressed during the administration period. Body weights recovered slowly on termination of administration.
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not examined
Neuropathological findings:
no effects observed
Description (incidence and severity):
In the acute study, Schwann’s sheath, Schwann’s cell and axon in sciatic nerve were essentially normal and no remarkable changes on nerve fiber, ganglionic cells and nissle granules in spinal cord.

In the repeated dose study, no abnormalities were found in the sciatic nerves and spinal cord.
Histopathological findings: non-neoplastic:
not examined
Histopathological findings: neoplastic:
not examined
Other effects:
no effects observed
Details on results:
In the positive control group, leg weakness, lack of leg coordination and loss of balance appeared on Days 12-14 and all hens showed well-developed leg paralysis in legs on Day 18. Histpathologically, degeneration of sciatic nerve fiber were observed.
Key result
Dose descriptor:
other:
Remarks on result:
not determinable due to absence of adverse toxic effects
Remarks:
There was no evidence of delayed neuropathy in this study
Key result
Critical effects observed:
no

Acute or sub-acute treatment with fenitrothion did not result in any symptoms of paralysis or neuropathology consistent with delayed neuropathy.

Conclusions:
No evidence of delayed neuropathy was seen under the conditions of this study.
Executive summary:

In a study of delayed neuropathy, groups of hens were adminstered single (500 mg/kg bw) or 28 repeated daily doses (16.7 or 33.4 mg/kg bw) fenitrothion. Hens were observed for 3 weeks after cessation of treatment and assessed histopathologically. Acute or sub-acute treatment with fenitrothion did not result in any symptoms of paralysis or neuropathology consistent with delayed neuropathy. Typical responses with the positive control compound TOCP confimed the sensitivity of the assay.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
12.5 mg/kg bw/day
Species:
rat
Quality of whole database:
A guideline-comparable study of acute neurotoxicity is available in the rat.

Effect on neurotoxicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Effect on neurotoxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Acute oral neurotoxicity

The acute oral neurotoxicity of fenitrothion was investigated in the rat. Groups of 12 or 13 male and 12 or 13 female Sprague-Dawley Crl:CD®(SD)BR rats received fenitrothion dissolved in corn oil, once by gavage at dose levels of 0, 12.5, 50 or 200 mg/kg bw for males and 0, 50, 200 or 800 mg/kg bw for females, at the dosage volume of 5 mL/kg bw. The animals were evaluated using a functional observation battery (FOB) and motor activity test on prestudy, days 0 (day of treatment, at the time of peak effect), 7 and 14. At the completion of the study (day 15), 6 animals/sex/group were randomly selected for perfusion and those in the control and high dose groups underwent a neuropathological evaluation. The remaining animals in each group had their brains removed and then were subjected to necropsy. The brain of each of these rats in the control, low dose and high dose groups was subsequently analyzed for glial fibrillary acidic protein (GFAP) content. One female in the 800 mg/kg bw group and one male in the 200 mg/kg bw group were found dead on Days 1 and 2, respectively. On the first few days following treatment, several abnormal clinical findings were observed such as wet fur staining along the ventral surface for the 200 and 800 mg/kg bw group rats and ocular discharge for the 200 mg/kg bw group males and one female from this same group, and for 800 mg/kg bw group females. For several male rats in the 200 mg/kg bw group, one female from this same group, and for most 800 mg/kg bw group females, the tremors persisted for a few days post dosing. A few 800 mg/kg bw group females also appeared dehydrated or had a prominent backbone. Aside from some occasional dry fur staining, no abnormal findings were evident beyond Day 4. The 200 mg/kg bw males had a significant decrease in body weights on all occasions following treatment compared to the control group.  The FOB performed on Day 0 found several significant differences between control and fenitrothion-treated groups, including tremors, gait incapacity, reduced locomotor activity levels and arousal, decreased rearing and reduced body temperature for 50 and 200 mg/kg bw males and females and 800 mg/kg bw females. Autonomic signs such as myosis and salivation, together with a reduced response to pain perception (toe and tail pinch tests), abnormal visual placing response, and delays for the positional passivity test and failed air righting reflex were also observed for the 50 mg/kg bw males, 200 mg/kg bw males and females, and 800 mg/kg bw females. An abnormal home cage body position observed as lying down on ventral surface also occurred for males in the 50 mg/kg bw and 200 mg/kg bw groups and for females in the 800 mg/kg bw group. In addition, quantitative measurements of limb strength showed reductions in the forelimb for 50 and 200 mg/kg bw males and 800 mg/kg bw females, and decreases in the hindlimb for 200 mg/kg bw males and females and 800 mg/kg bw females. Measurements on Day 0 indicated significant reductions in total activity counts for 50 and 200 mg/kg bw males, and 50, 200 and 800 mg/kg bw females. The linear constructed variable was similarly affected for the females. In addition, trend analysis on female data found a significant linear and quadratic dose level effect for total activity counts and the linear constructed variable. No significant differences were detected between the control and 12.5 mg/kg bw males. Gross necropsy did not reveal any effects of treatment; there was no treatment-related neuropathology. Glial fibrillary acidic protein content in the cerebral cortex of the 800 mg/kg group females was significantly elevated. The biological significance of this finding remains unclear given the variability of the data in both control and fenitrothion-treated groups, the increase in group mean was in part attributable to one rat with a high value, and that no structural changes in the nervous system were seen. A NOAEL of 12.5 mg/kg bw was determined for males based on signs in the qualitative clinical and functional observation, reduction in grip strength, body temperature and motor activity at 50 mg/kg bw. A NOAEL was not demonstrated for females.

Delayed neuropathy

In a study of delayed neuropathy, groups of hens were adminstered single (500 mg/kg bw) or 28 repeated daily doses (16.7 or 33.4 mg/kg bw) fenitrothion. Hens were observed for 3 weeks after cessation of treatment and assessed histopathologically. Acute or sub-acute treatment with fenitrothion did not result in any symptoms of paralysis or neuropathology consistent with delayed neuropathy. Typical responses with the positive control compound TOCP confimed the sensitivity of the assay.

Acute ocular toxicity

A non-standard study was performed to investigate the ocular toxicity of fenitrothion. Groups of SD rats (25/sex) were administered a single gavage dose of fenitrothion (in corn oil) at dose levels of 0, 20 or 200 mg/kg bw (males); 0, 40 or 400 mg/kg bw (females) and observed for up to 90 days. Signs of toxicity were observed and bodyweights measured. Opthalmology, histopathology of the eyes and ERG were performed at 4, 7, 14, 28 and 91 days after dosing. Cholinesterase activity was also measured. One mortality occurred in high dose males one hour following dosing. Signs of toxicity consistent with cholinesterase inhibition were observed in all treated groups. Inhibition of erythrocyte cholinesterase activity was shown in all treated groups. No acute ocular toxicity was detected in the rats given sub-lethal doses of fenitrothion which induced a remarkable inhibition of the cholinesterase activity and toxic signs.

Justification for classification or non-classification

Classification of fenitrothion on the basis of neurotoxic effects (cholinesterase inhibition) is proposed (STOT SE1, STOT RE1). No additional effects (neuropathology, neuropathy, ocular toxicity) were identified in these specific investigations.