Fenitrothion

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

16 December 1985 - 17 January 1986

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1986

Report date:

1986

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Fenitrothion

EC Number:

204-524-2

EC Name:

Fenitrothion

Cas Number:

122-14-5

Molecular formula:

C9H12NO5PS

IUPAC Name:

O,O-dimethyl O-3-methyl-4-nitrophenyl phosphorothioate

Test material form:

liquid

Specific details on test material used for the study:

Fenitrothion
Batch No.: 41208
Purity: 96.6%

Test animals

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Hazelton, Denver
- Age at study initiation: 4 months
- Weight at study initiation: 2.7-3.2 kg
- Housing: Individual
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 28 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18-23
- Humidity (%): 15-64
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 16 December 1985 To: 17 January 1986

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

Groups of 16 inseminated female HRA(NZW)SPF rabbits each received fenitrothion dissolved in corn oil, at dose levels of 0, 3, 10 and 30 mg/kg bw/d by oral gavage, daily from Days 7 to 19 of gestation at a dosage volume of 1.0 mL/kg bw.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Reserve samples of the dosing solutions were analysed for stability and achieved concentration.

Details on mating procedure:

Ovulation was induced in each females by iv injection of 250 IU HCG; females were inseminated with the sperm of males from the same strain on two occasions. The day of inseminatiom was designated GD0.

Duration of treatment / exposure:

GD7-19 (13 consecutive days).

Frequency of treatment:

Daily

Duration of test:

Dams were terminated on GD 29

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw/day

Remarks:

Vehicle control

Doses / concentrations 2

Dose / conc.:

3 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

10 mg/kg bw/day

Doses / concentrations 4

Dose / conc.:

30 mg/kg bw/day

No. of animals per sex per dose:

16 inseminated females

Control animals:

yes, concurrent vehicle

Details on study design:

Doses were selcetd on the basis of range-finding studies in pregnant and non-pregnant rabbits. Animals were assigned to the treatment groups using a weight randomisation technique.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily

BODY WEIGHT: Yes
- Time schedule for examinations: GD 0, 7, 8, 9, 13, 16, 19, 20, 23, 26, 29

FOOD CONSUMPTION: Yes
- Time schedule for examinations: GD 0, 7, 8, 9, 13, 16, 19, 20, 23, 26, 29

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 29

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes / No / No data
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: all per litter
- Skeletal examinations: Yes: all per litter
- Head examinations: Yes: all per litter

Statistics:

Data were analysed and test groups compared to the controls using appropriate statistical techniques

Indices:

Not applicable

Historical control data:

Not required for this study

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Anorexia was frequently noted in all groups during the treatment and posttreatment periods. Treatment-related clinical signs in rabbits receiving 30 mg/kg bw/d included reduction in motor activity, salivation, dyspnoea, and tremors. These signs were not seen in any animals of the control, 3 and 10 mg/kg bw/d groups at the pre-treatment and post-treatment intervals, with only one incidence of reduced motor activity (10 mg/kg bw/d group) noted during treatment, in the decedent rabbit.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, treatment-related

Description (incidence):

A total of six pregnant females receiving 30 mg/kg/ bwd were found dead during the treatment period and three pregnant females aborted or delivered prematurely (GD 22-29). One female receiving 10 mg/kg bw/d was found dead on GD18, and one control female was found dead on GD 8. Both females were anorexic prior to death. The two deaths in the 3 mg/kg bw/d group were the result of dosing errors (verified at necropsy).

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean body weight changes were significantly decreased for pregnant females receiving 30 mg/kg bw/d on GD7-13. These animals also displayed values slightly lower than the control for GD0-29 but this difference was not statistically significant.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Significantly decreased food consumption values were observed for pregnant females receiving 3 mg/kg bw/d on GD9-13 and were significantly increased for animals receiving 30 mg/kg bw/d on GD26-29 in addition to a significant negative trend on GD7-8. All other mean food consumption values were statistically similar for all groups.

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:

no effects observed

Description (incidence and severity):

The findings were considered to be incidental and not related to treatment.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Maternal developmental toxicity

Number of abortions:

effects observed, treatment-related

Description (incidence and severity):

Three pregnant females at 30 mg/kg bw/d aborted or delivered prematurely (GD 22-29).

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

no effects observed

Early or late resorptions:

no effects observed

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Changes in number of pregnant:

effects observed, treatment-related

Other effects:

no effects observed

Details on maternal toxic effects:

A total of six pregnant females receiving 30 mg/kg/ bwd were found dead during the treatment period and three pregnant females aborted or delivered prematurely (GD 22-29). One female receiving 10 mg/kg bw/d was found dead on GD18, and one control female was found dead on GD 8. Both females were anorexic prior to death. The two deaths in the 3 mg/kg bw/d group were the result of dosing errors (verified at necropsy). Anorexia was frequently noted in all groups during the treatment and posttreatment periods. Treatment-related clinical signs in rabbits receiving 30 mg/kg bw/d included reduction in motor activity, salivation, dyspnoea, and tremors. These signs were not seen in any animals of the control, 3 and 10 mg/kg bw/d groups at the pre-treatment and Mean body weight changes were significantly decreased for pregnant females receiving 30 mg/kg bw/d on GD7-13. These animals also displayed values slightly lower than the control for GD0-29 but this difference was not statistically significant.post-treatment intervals, with only one incidence of reduced motor activity (10 mg/kg bw/d group) noted during treatment, in the decedent rabbit. Significantly decreased food consumption values were observed for pregnant females receiving 3 mg/kg bw/d on GD9-13 and were significantly increased for animals receiving 30 mg/kg bw/d on GD26-29 in addition to a significant negative trend on GD7-8. All other mean food consumption values were statistically similar for all groups. Gross necropsy diod not reveal any effects of treatment.

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

body weight and weight gain

clinical signs

mortality

Maternal abnormalities

Key result

Abnormalities:

no effects observed

Results (fetuses)

Fetal body weight changes:

no effects observed

Reduction in number of live offspring:

effects observed, treatment-related

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

not examined

Changes in postnatal survival:

not examined

External malformations:

no effects observed

Skeletal malformations:

no effects observed

Visceral malformations:

no effects observed

Other effects:

no effects observed

Details on embryotoxic / teratogenic effects:

The mean number of implantations was lower in the high dose group, resulting in a lower litter size. Other parameters were unaffected by treatment. There was no dose-related increase in the incidence of any particular malformation or in the incidence of any type (i.e. external, visceral, or skeletal) of malformation. Although the litter incidence of skeletal malformations was slightly higher than controls in the 3 and 10 mg/kg bw/d groups, no malformations were noted in the seven litters of the 30 mg/kg bw/d group available for evaluation. Overt evidence of maternal toxicity was seen in animals receiving 30 mg/kg/ bwd but was not accompanied by adverse effects on fetal growth or development

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

reduction in number of live offspring

Fetal abnormalities

Key result

Abnormalities:

no effects observed

Overall developmental toxicity

Key result

Developmental effects observed:

yes

Lowest effective dose / conc.:

30 mg/kg bw/day

Treatment related:

yes

Relation to maternal toxicity:

developmental effects as a secondary non-specific consequence of maternal toxicity effects

Dose response relationship:

yes

Relevant for humans:

no

Any other information on results incl. tables

Summary of maternal findings

Dose level	0 mg/kg bw/d	3 mg/kg bw/d	10 mg/kg bw/d	30 mg/kg bw/d
GD 7-19 (treatment period)
Number of animals observed	16	16	16	16
Found dead	1	0	1	6
Accidental death	0	2	0	0
Reduction in motor activity	0	0	1	14
Salivation	0	0	0	14
Dyspnoea	0	0	0	14
Tremors	0	0	0	14
GD 20-29 (post-treatment period)
Number of animals observed	15	14	15	10
Premature delivery/abortion	0	0	0	3
Reduction in motor activity	0	0	0	1
Food consumption (g)
GD 0-7	1124	1137	1161	1183
GD 7-8	126	102	108	91
GD 8-9	138	112	134	104
GD 9-13	548	441*	531	465
GD 13-16	329	316	307	296
GD 16-19	364	221	307	294
GD 19-20	95	101	107	83
GD 20-23	385	372	372	403
GD 23-26	333	352	314	387
GD 26-29	278	396	307	457*
Bodyweight change (g)
GD 0-7	169	149	166	148
GD 7-8	-31	-42	-47	-48
GD 7-9	-10	-38	-18	-68
GD 7-13	51	-2	29	-62*
GD 7-16	45	33	61	-83
GD 7-19	92	-25	27	-73
GD 7-20	85	-9	35	-104
GD 7-23	168	63	87	4
GD 7-26	192	114	141	50
GD 7-29	228	203	192	141

*significantly different to controls (p<0.05)

Summary of litter parameters

Dose level	0 mg/kg bw/d	3 mg/kg bw/d	10 mg/kg bw/d	30 mg/kg bw/d
Number of females inseminated	16	16	16	16
Pregnancy rate (%)	87.5	93.8	100.0	100.0
No. of pregnant females	13	13	15	8
Number of litters with live foetuses	13	13	13	7
Mean number of corpora lutea	11.7	11.4	11.0	10.1
Mean number of implantations	8.3	7.6	8.3	5.7
Mean implantation efficiency (%)	72.5	67.9	76.8	61.5
Mean number of resorptions	1.7	1.2	1.3	1.1
Mean incidence of resorptions (%)	18.4	15.0	22.4	21.1
Mean incidence of foetal viability (%)	81.6	84.0	77.6	78.9
Mean number of live foetuses per litter	6.6	6.4	6.9	4.6
Mean number of dead foetuses per litter	0.0	0.1	0.0	0.0
Mean percent of males per litter	60.0	40.0	48.4	66.9
Mean fetal weight (g)
Male	44.6	43.6	41.1	48.0
Female	42.9	42.6	40.5	45.0

Summary of foetal findings

Dose level	0 mg/kg bw/d	3 mg/kg bw/d	10 mg/kg bw/d	30 mg/kg bw/d
Number of foetuses (fetal incidence %)
Total number of foetuses examined	86	83	104	32
External malformations	1 (1.2)	0 (0.0)	3 (2.9)	0 (0.0)
External variations	0 (0.0)	0 (0.0)	1 (1.0)	0 (0.0)
Visceral malformations	0 (0.0)	2 (2.4)	0 (0.0)	0 (0.0)
Visceral variations	4 (4.7)	1 (1.2)	5 (4.8)	1 (3.1)
Skeletal malformations	2 (2.3)	6 (7.2)	4 (3.8)	0 (0.0)
Skeletal variations	67 (78)	64 (77)	79 (76)	25 (78)
Number of litter (litter incidence %)
Total number of litters examined	13	13	13	7
External malformations	1 (7.7)	0 (0.0)	2 (15)	0 (0.0)
External variations	0 (0.0)	0 (0.0)	1 (7.7)	0 (0.0)
Visceral malformations	0 (0.0)	2 (15)	0 (0.0)	0 (0.0)
Visceral variations	3 (23)	1 (7.7)	4 (31)	1 (14)
Skeletal malformations	1 (7.7)	2 (15)	3 (23)	0 (0.0)
Skeletal variations	13 (100)	13 (100)	13 (100)	7 (100)

Applicant's summary and conclusion

Conclusions:

Maternal and developmental NOAELs of 10 mg/kg bw/d can be determined for this study, based on maternal toxicity (mortality, clinical signs, bodyweight effects) and reduced litter size at the highest dose level.

Executive summary:

In a developmental toxicity study, groups of 16 inseminated female HRA(NZW)SPF rabbits each received fenitrothion dissolved in corn oil, at dose levels of 0, 3, 10 and 30 mg/kg bw/d by oral gavage, daily from Days 7 to 19 of gestation at the dosage volume of 1.0 mL/kg bw. Clinical observations, body weights and food consumption were recorded for all females. On day 29 of gestation, all surviving pregnant females were sacrificed and a cesarean section performed. All live fetuses were evaluated for external findings, visceral findings (Staples' technique) and for skeletal findings following staining with Alizarin Red S. A total of six pregnant females receiving 30 mg/kg/ bwd were found dead during the treatment period and three pregnant females aborted or delivered prematurely (GD 22-29). One female receiving 10 mg/kg bw/d was found dead on GD18, and one control female was found dead on GD 8.  Both females were anorexic prior to death. The two deaths in the 3 mg/kg bw/d group were the result of dosing errors (verified at necropsy). Anorexia was frequently noted in all groups during the treatment and posttreatment periods. Treatment-related clinical signs in rabbits receiving 30 mg/kg bw/d included reduction in motor activity, salivation, dyspnoea, and tremors.  These signs were not seen in any animals of the control, 3 and 10 mg/kg bw/d groups at the pre-treatment and Mean body weight changes were significantly decreased for pregnant females receiving 30 mg/kg bw/d on GD7-13. These animals also displayed values slightly lower than the control for GD0-29 but this difference was not statistically significant.post-treatment intervals, with only one incidence of reduced motor activity (10 mg/kg bw/d group) noted during treatment, in the decedent rabbit.  Significantly decreased food consumption values were observed for pregnant females receiving 3 mg/kg bw/d on GD9-13 and were significantly increased for animals receiving 30 mg/kg bw/d on GD26-29 in addition to a significant negative trend on GD7-8.  All other mean food consumption values were statistically similar for all groups.  Gross necropsy did not reveal any effects of treatment. The mean number of implantations was lower in the high dose group, resulting in a lower litter size.  Other parameters were unaffected by treatment.  There was no dose-related increase in the incidence of any particular malformation or in the incidence of any type (i.e. external, visceral, or skeletal) of malformation. Although the litter incidence of skeletal malformations was slightly higher than controls in the 3 and 10 mg/kg bw/d groups, no malformations were noted in the seven litters of the 30 mg/kg bw/d group available for evaluation. Overt evidence of maternal toxicity was seen in animals receiving 30 mg/kg/ bwd but was not accompanied by adverse effects on foetal growth or development. Maternal and developmental NOAELs of 10 mg/kg bw/d can be determined for this study, based on maternal toxicity (mortality, clinical signs, bodyweight effects) and reduced litter size at the highest dose level.

The highest dose level in this study was sufficient to cause maternal toxicity (including mortality) and was associated with a slight reduction in implantations and litter size. Findings are considered to be secondary to maternal effects.