Chlorpyrifos

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1983

Report date:

1983

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The study was conducted to evaluate the teratogenic potential of the test substance when administered orally to bred rats during the period of major organogenesis (days 6 through 15 of gestation). Dams were sacrificed on day 21 of gestation and their concepti were examined for evidence of a teratogenic effect. A subgroup of 10 animals per dose level was sacrificed on day 15 of gestation to obtain plasma and erythrocyte levels of cholinesterase.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Chlorpyrifos

EC Number:

220-864-4

EC Name:

Chlorpyrifos

Cas Number:

2921-88-2

Molecular formula:

C9H11Cl3NO3PS

IUPAC Name:

O,O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate

Test material form:

solid

Specific details on test material used for the study:

AGR 190183
Purity: 96.6%

Test animals

Species:

rat

Strain:

Fischer 344

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Kingston, New York
- Weight: Approximately 175 to 220 g at breeding
- Housing: Housed in wire-bottomed cages
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: Atleast 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: Approximately 22°C
- Humidity: Approximately 50%
- Photoperiod: 12 hrs dark /12 hrs light

Administration / exposure

Route of administration:

oral: gavage

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Test solutions were prepared by dissolving the test material in corn oil such that a dose volume of 4 mL/kg of body weight/day yielded the appropriate dose level.

Analytical verification of doses or concentrations:

no

Details on mating procedure:

- Impregnation procedure: Cohoused
- M/F ratio per cage: 1:1
- Verification of same strain and source of both sexes: Yes
- Proof of pregnancy: Sperm in vaginal smear referred to as day 0 of gestation

Duration of treatment / exposure:

G6 to G15

Frequency of treatment:

Daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0.1 mg/kg bw/day

Doses / concentrations 2

Dose / conc.:

3 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

15 mg/kg bw/day

No. of animals per sex per dose:

31, 31, 32 and 33 bred rats at dose levels of 0, 0.1, 3.0 and 15 mg/kg respectively

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

OBSERVATIONS: Animals were observed daily throughout the experi~ental period for indications of toxicity

BODY WEIGHT: Body weights for rats were recorded on gestation days 6 through 16 and on day 21 of gestation

FOOD CONSUMPTION AND WATER CONSUMPTION: Food and water consumption were recorded for each rat at 3-day intervals starting on day 6 of gestation.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- number and position of fetuses in utero
- number of live and dead fetuses
- number and position of resorption sites
- the number of corpora lutea
- the sex, body weight and crown-rump length of each fetus
- any gross external alteration

Fetal examinations:

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

Statistics:

Body weights, food and water consumption, hematological parameters, and absolute and relative organ weights were evaluated by Bartlett's test for equality of variances. Based upon the outcome of Bartlett's test, a parametric or nonparametric analysis of variance (ANOVA) was performed followed by Dunnett's test or followed by the Wilcoxon Rank-Sum test With Bonferroni's correction (Steel and Torrie, 1960) if the ANOVA was significant. Statistical evaluation of the frequency of pre-implantation loss and of resorptions among litters and the fetal population was made by a censored Wilcoxon test (Haseman and Hoel, 1974) with Bonferroni's correction. Other incidence data were analyzed by the Fisher exact probability test (Siegel, 1956).

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Clinical signs of maternal toxicity including excessive salivation, urine staining in the perineal region, porphyrin deposits about the eyes, vaginal bleeding and tremors were noted throughout the dosing period among animals in the 15 mg/kg/day dose group. However, all animals survived until their scheduled necropsy. No effects on the general appearance or demeanor of animals in the control, 0.1 or 3.0 mg/kg/day dose groups were noted.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Overall, the high dose rats gained less weight than did the control rats. Statistical decreases were noted in body weight gain on days 9 through 11 and body weights on days 12 and 16. Body weights at 0.1 and 3.0 mg/kg/day levels were comparable to controls throughout the study.

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

No significant effect on the weight of the liver was observed at any dose level

Other effects:

effects observed, treatment-related

Description (incidence and severity):

Data collected from groups of 10 bred rats/dose level that were necropsied on day 15 of gestation indicated that cholinesterase levels in the plasma and erythrocytes were significantly decreased among rats given 3 or 15 mg/kg/day. Cholinesterase levels in the plasma of rats from the 3 and 15 mg/kg/day dose groups were found to be only 10 and 3 percent (respectively) of the plasma cholinesterase levels in the control animals. Mean erythrocyte cholinesterase levels of animals in the 3 and 15 mg/kg/day dose groups were found to be 25 and 20 percent (respectively) of the control group mean. No effect on cholinesterase levels was observed among rats receiving 0.1 mg/kg/day.

Maternal developmental toxicity

Pre- and post-implantation loss:

effects observed, non-treatment-related

Description (incidence and severity):

Upon staining with sodium sulfide stain, implantation sites which had undergone resorption daily in gestation were detected in the uterus of one rat from the 15 mg/kg/day dose group.

Total litter losses by resorption:

no effects observed

Details on maternal toxic effects:

No adverse effects on litter size, resorption rate, fetal body weight or fetal crown-rump length were observed among any of the treatment groups.

Effect levels (maternal animals)

Key result

Remarks on result:

other: Severe maternal toxicity was observed among rats given 15 mg/kg/day

Results (fetuses)

Fetal body weight changes:

no effects observed

Reduction in number of live offspring:

no effects observed

Changes in litter size and weights:

no effects observed

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Several malformations were observed scattered throughout the dose levels at incidences consistent with the historical background observed in this laboratory. Microphthalmia (small eyes) was observed in one fetus in the control group, in one fetus in the 3.0 mg/kg group and in 2 fetuses in the 15 mg/kg dose group. Anopthalmia (eye absent) was observed in one fetus from the control group and in one fetus from the 3.0 mg/kg dose group. One fetus from the 0.1 mg/kg dose group exhibited fused ribs. A single case of cleft palate (soft-palate) was observed in a fetus from in the 15 mg/kg dose group.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

No significant effect was observed on the skeletal development of fetuses. Variations observed also appeared to be randomly distributed throughout the dose groups and included extra site of ossification near the sternebrae (one control fetus) and lumbar spurs (2 control fetuses, 4 fetuses in 0.1 mg/kg, 2 fetuses in 15 mg/kg).

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Three fetuses from a different litter in the 15 mg/kg/day dose group exhibited severely dilated renal pelvis. Variations observed also appeared to be randomly distributed throughout the dose groups and included patent ductus arteriosous (one control fetus), hemorrhage of the liver (one fetus in 0.1 mg/kg), convoluted ureter (one fetus in 0.1 mg/kg and 2 in 15 mg/kg group)

Effect levels (fetuses)

Key result

Remarks on result:

other: No evidence of embryo or fetotoxicity was observed at any of the dose levels

Overall developmental toxicity

Key result

Developmental effects observed:

no

Applicant's summary and conclusion

Conclusions:

Test substance was not considered teratogenic in rats at levels up to 15 mg/kg/day, a maternally toxic level.

Executive summary:

The objective of this study was to evaluate the teratogenic potential of the test substance when administered orally to bred rats during the period of major organogenesis. Bred rats received 0, 0.1, 3.0 or 15 mg/kg body weight/day on days 6 through 15 of gestation. Dams were sacrificed on day 21 of gestation and their concepti were examined for evidence of a teratogenic effect. A subgroup of 10 animals per dose level was sacrificed on day 15 of gestation to obtain plasma and erythrocyte levels of cholinesterase.

Oral administration of the test substance at a dose level of 0.1 mg/kg/day to bred rats did not produce any evidence of maternal toxicity. Cholinesterase levels were significantly depressed among rats in the 3.0 mg/kg/day dose group but no other signs of toxicity were observed in this group. Severe maternal toxicity was observed among rats given 15 mg/kg/day. Cholinesterase levels were drastically reduced compared to controls and clinical signs of organophosphate poisoning (excessive salivation, urination, defecation, and lacrimation) were observed. No evidence of embryo- or fetotoxicity or increase incidence of malformations was observed at any dose level. Based on these data, the test substance was not considered teratogenic in rats at levels up to 15 mg/kg/day, a maternally toxic level.