Pirimiphos-methyl

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1985

Report date:

1985

Materials and methods

Test guideline

Test guideline 1

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Test guideline 2

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method B.31 (Prenatal Developmental Toxicity Study)

Test guideline 3

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OPP 83-3 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Pirimiphos-methyl

EC Number:

249-528-5

EC Name:

Pirimiphos-methyl

Cas Number:

29232-93-7

Molecular formula:

C11H20N3O3PS

IUPAC Name:

O-2-(diethylamino)-6-methylpyrimidin-4-yl O,O-dimethyl phosphorothioate

Test animals

Species:

rat

Strain:

other: Alpk:AP

Remarks:

Wistar-derived

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: approx. 12 weeks
- Weight at study initiation: 218-313 g
- Housing: individually housed in rat racks. The cages had solid stainless steel sides and the floor, back and front were constructed of stainless steel mesh. The internal measurements were 34.0 x 37.5 x 20.3 cm. The cages were suspended over collecting trays lined with absorbent paper.
- Diet: CT1 diet, ad libitum
- Water: ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 - 24
- Humidity (%): 50 - 61
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test substance was administered in corn oil. The concentration of the test substance was adjusted to give a constant dose volume of 1 mL/100 g body weight for each level dose. An appropriate amount of corn oil was added to a weighted amount of the test substance to form two 600 mL volume preparations per dose level.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

A sample of each preparation was analysed prior to the start of dosing to verify the achieved concentration of the test substance in corn oil. At the end of the dosing period samples of each preparation were analysed to determine the residual concentrations of the test substance. The chemical stability of the test substance was determined by re-analysis of the dosing formulations containing nominally 0.15 and 15.0 mg/mL after an interval of 28 days. Analysis was by acetone dilution followed by gas chromatography.

Details on mating procedure:

- Impregnation procedure: purchased timed pregnant
- Proof of pregnancy: sperm in vaginal smear referred to as day 1 of pregnancy

Duration of treatment / exposure:

Days 7-16 inclusive of gestation

Frequency of treatment:

Daily

Duration of test:

15 days (gestation day 7 - 22)

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

1.5 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

15 mg/kg bw/day (nominal)

Doses / concentrations 3

Dose / conc.:

150 mg/kg bw/day (nominal)

No. of animals per sex per dose:

24 females per dose group

Control animals:

yes, concurrent vehicle

Details on study design:

All animals were dosed from Days 7-16 inclusive of gestation with 1 mL of dosing formulations per 100 g body weight using a 5 mL disposable syringe and a stainless steel 16 gauge cannula. The volume given to each animal was adjusted daily according to body weight. Control animals received the appropriate volume of corn oil. Dosing was performed in the morning of each day.

Examinations

Maternal examinations:

DETAILED CLINICAL OBSERVATIONS:
- Time schedule: daily

BODY WEIGHT:
- Time schedule for examinations: Days 1 and 4 and subsequently on Days 7-16 (inclusive) and on Days 19 and 22 of gestation

FOOD CONSUMPTION:
The amount of food consumed by each animal over three day periods was measured by giving a weighed quantity of food contained in a glass jar on Days 1, 4, 7, 10, 13, 16 and 19 and calculating the amount consumed from the amount left on Days 4, 7, 10, 13, 16, 19 and 22 respectively.

POST-MORTEM EXAMINATIONS:
- One animal in the 150 mg/kg bw/day group was found dead during the study. This animal was given a macroscopic post mortem examination and pregnancy status was recorded.
- Sacrifice on gestation day # 22
- Organs examined: The intact gravid uterus (minus ovaries and trimmed free of connective tissue) was removed and weighed. The ovaries and uterus were then examined and the number of corpora lutea in each ovary as well as number and position of implantation was recorded.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
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
- Other: The implantations were assigned letters of the alphabet to identify their position in utero starting at the ovarian end of the left horn and ending at the ovarian end of the right horn.

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:

See 'Any other information on materials incl. tables'

Indices:

% Pre-implantation loss = ((No. of corpora lutea - No. of implantations)/No. of corpora lutea) x 100
% Post-implantation loss = ((No. of implantations - No. of live foetuses)/No. of implantations) x 100

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

In the 150 mg/kg/day group changes in clinical condition were observed in twenty of the twenty three surviving animals. These changes included abnormal gait, changes in behaviour, signs of urinary incontinence, piloerection and body tremors and they were considered to have been induced by treatment.
There was no evidence of any adverse effects of treatment with either 1.5 or 15 mg/kg/day test substance.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, treatment-related

Description (incidence):

All but one animal in the 150 mg/kg/day group survived the duration of the study. This female was found dead on day 19 of gestation having shown some weight loss from day 13 and changes in clinical condition on day 16. These changes included abnormal gait, body tremors, piloerection, signs of urinary incontinence and irregular breathing. Post mortem examination revealed changes in the lungs and in the gastro-intestinal tract which may have been due to autolysis. The death of this animal was considered to be treatment-related.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Administration of 150 mg/kg/day test substance was associated with a statistically significant reduction in body weight gain compared with the control group during the dosing and the post dosing period. The effect was most marked between days 13 and 16 of the dosing period and days 16 and 19 of the post dosing period. Between days 19 and 22, weight gain was comparable with the control group.
There were no adverse effects of treatment on maternal weight gain with either 1.5 or 15 mg/kg/day test substance

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Administration of 150 mg/kg/day test substance was associated with a statistically significant reduction in food consumption compared with the control group for the dosing period and the post dosing period. The effect attained statistical significance from day 13 onwards.
There were no adverse effects of treatment on maternal food consumption with either 1.5 or 15 mg/kg/day test substance.

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

Endocrine 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:

effects observed, non-treatment-related

Description (incidence and severity):

Only two animals in the 1.5 mg/kg/day group surviving to termination showed any macroscopic changes post mortem. One female had bilateral renal pelvic dilatation and another female had dark red fluid surrounding the foetuses in utero. These changes were of the type commonly seen in the Alpk:AP strain of rat and were considered not to be treatment-related.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Other effects:

not examined

Maternal developmental toxicity

Number of abortions:

no effects observed

Pre- and post-implantation loss:

effects observed, non-treatment-related

Description (incidence and severity):

In the 1.5 mg/kg/day group, pre-implantation loss was statistically significantly increased compared with the control group. Consequently, the mean number of implantations and of live foetuses and hence, mean gravid uterus and litter weight, were all statistically significantly reduced. These values were nevertheless within the range expected for control rats of this strain and in the absence of a dosage-related trend, these observations were considered to be of no toxicological significance.

Total litter losses by resorption:

not examined

Early or late resorptions:

no effects observed

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Changes in number of pregnant:

not examined

Other effects:

not examined

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

15 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

body weight and weight gain

clinical signs

food consumption and compound intake

mortality

Maternal abnormalities

Key result

Abnormalities:

no effects observed

Results (fetuses)

Fetal body weight changes:

no effects observed

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

effects observed, non-treatment-related

Description (incidence and severity):

In the 150 mg/kg/day group, the proportion of foetuses which were male was statistically significantly increased in comparison with the control when analysed on a foetus basis but not when analysed on a litter basis. The values for all groups including the control group were however, within the historical control range for this strain of rat and therefore, no adverse effects of treatment with the test substance were considered likely.

Changes in litter size and weights:

no effects observed

Anogenital distance of all rodent fetuses:

no effects observed

Changes in postnatal survival:

not examined

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

The incidence of foetuses with major defects was 1, 0, 0 and 2 in the control, 1.5, 15 and 150 mg/kg bw/day groups, respectively. The defects were not similar in type and there was no evidence to suggest that their occurence was due to treatment with the test substance.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

The incidence of foetuses with fully ossified 4th lumbar transverse processes was statistically significantly increased in the 1.5 and 150 mg/kg/day groups in comparison with the control group. In the absence of any dosage-relationship, this finding was considered to be unrelated to treatment. The mean manus and pes scores for the treated groups were not statistically significantly different from the control group. The pes scores for the
150 mg/kg/day group did, however, reflect a very slight reduction in ossification compared with the control group.

Visceral malformations:

no effects observed

Other effects:

not examined

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

15 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

skeletal malformations

Fetal abnormalities

Key result

Abnormalities:

no effects observed

Overall developmental toxicity

Key result

Developmental effects observed:

yes

Lowest effective dose / conc.:

150 mg/kg bw/day (nominal)

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:

yes

Any other information on results incl. tables

Table 1. Clinical signs of toxicity seen in dams

Dose (mg/kg bw/d)	0	1.5	15	150
Number examined	24	24	24	24
Maternal b wt gain (g)	152.5	149.3	157.9	109.5**
Maternal food consumption (g/day)	515.5	513.7	524.5	433.7**
	Number showing effect
Increased activity	0	0	0	1
Increased response to touch	0	0	0	1
Splayed gait	0	0	0	4
Tip toe gait	0	0	0	4
Reduced stability	0	0	0	2
Tremors	0	0	0	7
Hunched	0	0	0	1
Subdued	0	0	0	6
Decreased abdominal tone	0	0	0	1
Piloerection	1	0	3	14
Irregular breathing	0	0	0	2
Signs of salivation	0	0	0	1
Stains around nose	0	0	0	4
Signs of urinary incontinence	0	0	0	13

 

Table 2. Foetal ‘Pes’ scores

Dose (mg/kg bw/d)	0	1.5	15	150
Mean Pes score	2.93	2.78	2.92	3.07

Applicant's summary and conclusion

Conclusions:

There was no evidence of teratogenicity in this study with any of the dose levels of the test substance used. Administration of 150 mg/kg bw/day was associated with maternal toxicity and with minimal foetotoxicity.
There were no adverse effects of treatment with either 1.5 or 15 mg/kg bw/day test substance, therefore, the NOAEL for maternal toxicity and teratogenicity is 15 mg/kg bw/day.

Executive summary:

In a GLP compliant study, comparable to OECD TG 414, groups of 24 pregnant female rats were dosed by gavage with 0, 1.5, 15 or 150 mg/kg bw/day test substance in corn oil from days 7-16 (inclusive) of gestation which thus included the period of major organogenesis. The day of confirmation of mating was designated Day 1 of gestation. On Day 22 of gestation the females were killed and their uteri examined for live foetuses and intra-uterine deaths.

The foetuses were weighed, examined for external and visceral abnormalities, sexed, eviscerated and stained for skeletal examination. Administration of 150 mg/kg bw/day test substance was associated with maternal toxicity manifest as treatment-related changes in clinical condition, reduced bodyweight gain and food consumption. There was no evidence of maternal toxicity associated with either 1.5 or 15 mg/kg bw/day administration of the test substance. There were no effects of the test substance on the number, growth and survival of the young in utero with any of the dose levels used. There was no evidence of teratogenicity or foetotoxicity associated with the administration of 1.5, 15 or 150 mg/kg bw/day test substance as assessed by the type and incidence of major defects and the incidence of minor defects and variants. There was however, some minimal evidence of foetotoxicity with 150 mg/kg bw/day dose manifest as marginal reduction in the ossification of the pes. In conclusion, administration of 150 mg/kg bw/day test substance was associated with maternal toxicity and with minimal evidence of foetotoxicity (as a result of maternal toxicity). There were no adverse effects of treatment with either 1.5 or 15 mg/kg bw/day test substance, therefore, the NOAEL for maternal toxicity and teratogenicity is 15 mg/kg bw/day.