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Toxicological information

Repeated dose toxicity: oral

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Administrative data

Endpoint:
sub-chronic toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
30 June 1992 - 2 October 1992
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1993
Report Date:
1993

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
EPA OPP 83-1 (Chronic Toxicity)
Deviations:
no
Qualifier:
according to
Guideline:
other: EPA OPP 82-7
Deviations:
no
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Specific details on test material used for the study:
Fenitrothion
Batch No.: 90617
Purity: 94.3 %

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on species / strain selection:
Standar strain and species
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Canada
- Females nulliparous and non-pregnant: yes
- Age at study initiation: 50-53 days
- Weight at study initiation: 237-289 g (males), 168-215 g (females )
- Fasting period before study: None
- Housing: Individual
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: at least 15 days

DETAILS OF FOOD AND WATER QUALITY:

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-24
- Humidity (%): 30-70
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: 30 June 1992 - 2 October 1992

Administration / exposure

Route of administration:
oral: feed
Details on route of administration:
Dietary incorporation
Vehicle:
unchanged (no vehicle)
Details on oral exposure:
Dietary concentrations were 0, 6, 20, 60 and 200 ppm; corresponding to 0, 0.40, 1.32, 3.99 and 13.8 mg/kg bw/d in males; 0, 0.46, 1.56, 4.85 and 17.6 mg/kg bw/d in females.
Analytical verification of doses or concentrations:
yes
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
Daily (continuous)
Doses / concentrationsopen allclose all
Dose / conc.:
0 ppm
Remarks:
Control (basal diet)
Dose / conc.:
6 ppm
Remarks:
0.40 and 0.46 mg/kg bw/d in males and females, respectively
Dose / conc.:
20 ppm
Remarks:
1.32 and 1.56 mg/kg bw/d in males and females, respectively
Dose / conc.:
60 ppm
Remarks:
3.99 and 4.85 mg/kg bw/d in males and females, respectively
Dose / conc.:
200 ppm
Remarks:
13.8 and 17.6 mg/kg bw/d in males and females, respectively
No. of animals per sex per dose:
12/sex (main groups)
15/sex (cholinesterase activity assessment)
Control animals:
yes, concurrent no treatment
Details on study design:
Groups of 12 male and 12 female Sprague-Dawley rats for the main study and groups of 15 male and 15 female Sprague-Dawley rats for cholinesterase assessment received fenitrothion, in powdered Certified PMI Rodent Chow at concentrations of 0, 6, 20, 60 and 200 ppm (corresponding to 0, 0.40, 1.32, 3.99 and 13.8 mg/kg bw/d in males; 0, 0.46, 1.56, 4.85 and 17.6 mg/kg bw/day in females) for 13 weeks.
Positive control:
Not required

Examinations

Observations and examinations performed and frequency:
All animals were observed twice a day for their toxic signs and mortality. Body weight was recorded weekly and days of behavioural testing. Food consumption was recorded weekly for all animals.

Main study animals: Functional observational battery (FOB) and motor activity were tested at prestudy and 4th, 8th and 13th weeks of treatment.

Cholinesterase test animals: Erythrocyte, plasma and brain cholinesterase activities were determined on 5 rats/sex/group at 4, 8 and 13 weeks.
Sacrifice and pathology:
At the completion of the study, 6 rats/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 (6/sex) had their brains removed and then were subjected to necropsy. The brain of each of non-perfused rats in the control and high dose groups was subsequently analyzed for glial fibrillary acidic protein (GFAP).
Statistics:
Study parameters were assessd and compared to controls using appropriate statistical analyses.

Results and discussion

Results of examinations

Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
Four females in the 200 ppm group showed tremors on one or two days during the second week of treatment. The 200 ppm group females also showed a higher incidence of muzzle staining and brown staining along the tail during the study compared to the control group.
Mortality:
no mortality observed
Description (incidence):
No animals died and none were sacrificed prior to study completion
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Both males and females in the 200 ppm group and females in the 60 ppm group had significantly reduced body weights compared to the control group on Day 7. The 200 ppm group's body weight remained significantly lower on Day 14 and 21 for males and from Days 7 to 42 for females
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
Food consumption by the 200 ppm group males and females were significantly lower than the control group from Days 0 to 7. Food consumption by the 200 ppm group females remained significantly reduced from Days 7 to 14 but then increased significantly from Days 28 to 56 and from 84 to 91.
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:
effects observed, treatment-related
Description (incidence and severity):
Reductions in blood and brain cholinesterase levels were noted for males in the 60 and 200 ppm groups and females in the 20, 60 and 200 ppm groups.
Urinalysis findings:
not examined
Behaviour (functional findings):
effects observed, non-treatment-related
Description (incidence and severity):
No significant differences considered to be related to treatment were seen for the qualitative components of the FOB. Significantly lower values for the 200 ppm group females in forelimb grip strength during the 4th week and in hindlimb grip strength during the 8th week occurred. These differences were considered not to be indicative of neurotoxicity taking lower body weights for the 200 ppm group females. Body temperature values as well as motor activity levels were not significantly different between control and fenitrothion-treated groups.
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
Description (incidence and severity):
No gross pathological findings or neuropathological changes (including brain measurements) seen were attributed to treatment with fenitrothion. No significant increases in glial fibrillary acidic protein were detected between the control and high dose groups for either male or females.
Histopathological findings: non-neoplastic:
no effects observed
Histopathological findings: neoplastic:
no effects observed
Other effects:
no effects observed

Effect levels

Key result
Dose descriptor:
NOAEL
Effect level:
20 ppm
Based on:
test mat.
Sex:
male/female
Basis for effect level:
clinical biochemistry

Target system / organ toxicity

Key result
Critical effects observed:
yes
Lowest effective dose / conc.:
60 ppm
System:
nervous system
Organ:
neurons
Treatment related:
yes
Dose response relationship:
yes
Relevant for humans:
yes

Any other information on results incl. tables

Summary of bodyweights (g)

Dose level

0 ppm

6 ppm

20 ppm

60 ppm

200 ppm

Males

 

 

 

 

 

Day  0

264.2

262.7

265.3

266.0

263.6

Day  7

318.4

314.7

320.6

319.6

298.4**

Day 14

359.4

355.1

364.3

362.5

336.8**

Day 21

388.6

384.7

395.2

394.9

372.3*

Day 26

413.1

410.9

421.6

417.7

393.1

Day 27

409.3

406.0

419.0

415.4

392.5

Day 28

414.0

409.8

423.8

421.1

401.7

Day 35

439.1

428.7

453.3

447.8

429.5

Day 42

465.2

454.5

475.0

473.5

456.8

Day 49

488.2

472.8

496.0

494.2

479.1

Day 54

503.2

495.3

511.1

509.7

484.4

Day 55

496.6

492.9

508.4

505.3

482.3

Day 56

502.2

488.3

512.1

506.4

497.4

Day 63

518.8

503.1

254.2

524.5

509.1

Day 70

536.7

520.4

539.1

541.2

525.5

Day 77

553.6

538.6

553.6

558.7

539.7

Day 84

563.4

549.3

564.8

570.6

552.3

Day 89

569.5

570.8

581.6

584.5

554.7

Day 90

563.2

564.4

573.0

579.3

551.2

Day 91

566.8

556.0

569.7

577.7

558.8

Females

 

 

 

 

 

Day  0

189.2

188.9

186.8

185.6

186.5

Day  7

213.8

211.3

209.0

204.9*

186.0**

Day 14

226.8

226.4

225.4

219.9

190.2**

Day 21

244.1

242.7

238.1

234.7

210.6**

Day 26

249.7

251.4

246.6

243.4

216.2**

Day 27

251.3

250.7

247.8

242.5

215.4**

Day 28

255.9

253.2

248.1

246.5

226.4**

Day 35

269.3

264.8

261.0

257.4

246.4**

Day 42

280.8

276.5

270.5

268.6

216.8*

Day 49

290.8

280.4

277.0

279.6

277.1

Day 54

288.6

283.3

279.3

284.3

271.2

Day 55

287.1

280.4

277.9

282.7

268.5

Day 56

295.8

286.1

279.1

284.9

282.2

Day 63

300.7

292.5

288.6

296.5

284.7

Day 70

307.0

300.6

291.4

304.2

291.6

Day 77

314.0

308.0

301.5

313.0

299.8

Day 84

319.0

313.6

306.3

315.8

305.3

Day 89

319.1

313.8

306.2

317.3

305.5

Day 90

316.5

311.0

302.9

312.3

302.8

Day 91

318.4

312.2

304.7

315.6

307.2

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

Summary of food consumption (g/day)

Dose level

0 ppm

6 ppm

20 ppm

60 ppm

200 ppm

Males

 

 

 

 

 

Day  0 - 7

196.5

194.7

201.6

200.9

182.2**

Day  7 - 14

203.2

197.2

208.9

207.7

194.8

Day  14 - 21

206.3

202.9

212.0

211.5

209.5

Day  21 - 28

202.2

199.0

204.5

204.8

211.2

Day  28 - 35

204.2

199.0

210.9

204.8

211.8

Day  35 - 42

213.2

199.4

204.1

209.8

214.8

Day  42 - 49

217.0

197.9**

208.5

211.9

213.3

Day  49 - 56

208.8

197.0

205.3

206.0

213.3

Day  56 - 63

211.1

200.5

207.7

208.1

213.6

Day  63 - 70

215.3

203.1

205.5

207.0

210.1

Day  70 - 77

215.6

205.4

206.2

211.9

210.6

Day  77 - 84

208.9

204.3

207.5

214.9

215.3

Day  84 - 91

199.6

194.7

199.3

204.0

206.7

Females

 

 

 

 

 

Day  0 - 7

139.3

137.1

137.5

135.7

119.3**

Day  7 - 14

143.3

138.8

142.3

140.4

100.9**

Day  14 - 21

151.1

149.9

145.7

148.1

145.2

Day  21 - 28

145.7

141.9

140.8

143.9

154.4

Day  28 - 35

149.6

141.0

141.9

151.2

167.4**

Day  35 - 42

152.9

145.4

141.4

150.4

173.9**

Day  42 - 49

151.6

143.1

146.8

153.9

180.7**

Day  49 - 56

148.2

141.6

139.1

147.5

164.8**

Day  56 - 63

150.4

147.3

145.1

159.1

165.8

Day  63 - 70

151.8

145.0

143.8

153.6

160.3

Day  70 - 77

152.0

145.9

146.2

153.0

163.2

Day  77 - 84

149.6

146.8

145.9

150.3

161.2

Day  84 - 91

142.9

139.8

135.6

145.8

159.9*

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

Summary of FOB

Dose level

0 ppm

6 ppm

20 ppm

60 ppm

200 ppm

Females

 

 

 

 

 

Forelimb grip strength (g)

 

 

 

Week 3

1120.4

1095.0

1100.0

1084.2

998.8**

Week 7

1091.3

1111.3

1066.7

1102.5

1036.3

Week 12

1182.5

1157.1

1051.3

1036.7

971.7

Hindlimb grip strength (g)

 

 

 

Week 3

773.3

797.1

760.0

765.8

737.5

Week 7

766.3

792.5

755.8

726.3

658.8**

Week 12

908.3

982.1

915.0

884.6

808.8

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

Summary of cholinesterase activity

Dose level

0 ppm

6 ppm

20 ppm

60 ppm

200 ppm

Males

 

 

 

 

 

Plasma cholinesterase (U/L)

 

 

 

Week 4

349.0

350.4

292.2

220.0**

181.4**

Week 8

379.0

299.0

295.4

196.0*

155.8**

Week 13

359.5

299.8

313.0

231.2*

216.6**

Erythrocyte cholinesterase (U/L)

 

 

 

Week 4

2255.0

2117.0

2131.4

1711.0*

1206.4**

Week 8

2106.0

2054.8

1839.8

1519.4**

1205.8**

Week 13

2186.5

1978.0

1978.8

1815.0

1299.2**

Brain cholinesterase (U/L)

 

 

 

Week 4

10.06

10.08

9.62

8.00**

3.52**

Week 8

8.30

7.60

8.66

7.19

3.49**

Week 13

9.53

9.26

9.51

8.18**

4.00**

Females

 

 

 

 

 

Plasma cholinesterase (U/L)

 

 

 

Week 4

1533.0

1194.6

720.4

513.4*

314.0***

Week 8

2159.4

1914.4

938.8**

505.6**

324.8**

Week 13

2888.4

1396.0

976.2

661.8**

376.8***

Erythrocyte cholinesterase (U/L)

 

 

 

Week 4

2331.6

2218.6

1880.4*

1499.6**

1162.2**

Week 8

1601.0

1589.8

1332.6

1175.8

822.5

Week 13

1650.0

1889.8

1668.2

1217.6

1021.8

Brain cholinesterase (U/L)

 

 

 

Week 4

10.23

9.74

8.72*

4.58**

2.12**

Week 8

9.13

8.74

8.08

3.89**

2.01**

Week 13

9.40

9.62

8.92

3.99**

2.18**

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

Applicant's summary and conclusion

Conclusions:
A NOAEL of 20 ppm (equivalent to 1.32 and 1.56 mg/kg bw/d in males and females respectively) can be determined for this study based on the inhibition of cholinesterase activity at higher dietary concentrations.
Executive summary:

The neurotoxicity of fenitrothion was investigated in a 90 -day rat study. Groups of 12 male and 12 female Sprague-Dawley rats (main study) and groups of 15 male and 15 female rats (cholinesterase assessment) received fenitrothion in the diet at concentrations of 0, 6, 20, 60 and 200 ppm. Dietary concentrations were calculated to be equal to mean intakes of 0, 0.40, 1.32, 3.99 and 13.8 mg/kg bw/d in males; 0, 0.46, 1.56, 4.85 and 17.6 mg/kg bw/d in females) for 13 weeks. All animals were observed twice a day for their toxic signs and mortality. Body weight was recorded weekly and days of behavioral testing. Food consumption was recorded weekly for all animals. Functional observational battery (FOB) and motor activity assessments were performed pre-test and during Weeks 4, 8 and 13.  At termination, 6 rats/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 (6/sex) had their brains removed and then were subjected to necropsy. The brain of each of non-perfused rats in the control and high dose groups was subsequently analyzed for glial fibrillary acidic protein (GFAP). Cholinesterase activities (erythrocyte, plasma, brain) were measured at 4, 8 and 13 weeks (5/sex). No animal died and none were sacrificed prior to scheduled termination. No treatment-related toxic signs were noted in male rats. Four females in the 200 ppm group showed tremors on one or two days during the second week of treatment. The 200 ppm group females also showed a higher incidence of muzzle staining and brown staining along the tail during the study compared to the control group. Both males and females in the 200 ppm group and females in the 60 ppm group had significantly reduced body weights compared to the control group on Day 7. The 200 ppm group's mean body weight remained significantly lower on Day 14 and 21 for males and from Days 7 to 42 for females. Food consumption for the 200 ppm group males and females were significantly lower than the control group from Days 0 to 7. Food consumption for the 200 ppm group females remained significantly reduced from Days 7 to 14 but then increased significantly from Days 28 to 56 and from 84 to 91. No significant differences considered to be related to treatment were seen for the qualitative components of the FOB. Significantly lower values for the 200 ppm group females in forelimb grip strength during the 4th week and in hindlimb grip strength during the 8th week occurred. These differences were considered not to be indicative of neurotoxicity taking lower body weights for the 200 ppm group females. Body temperature values as well as motor activity levels were not significantly different between control and fenitrothion-treated gropus. Reductions in blood and brain cholinesterase levels were noted for males in the 60 and 200 ppm groups and females in the 20, 60 and 200 ppm groups. No gross pathological findings or neuropathological changes (including brain measurements) seen were attributed to treatment with fenitrothion. No significant increases in glial fibrillary acidic protein were detected between the control and high dose groups for either male or females. A NOAEL of 20 ppm (equivalent to 1.32 and 1.56 mg/kg bw/d in males and females respectively) can be determined for this study based on the inhibition of cholinesterase activity at higher dietary concentrations.