2,4-dichlorophenol

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24th Aug 1982 - 4th October 1982

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study was conducted in accordance with GLP, OECD and proposed guidelines for registration of pesticides in the United States.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1983

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

The study did not contain data on food comsumption. However it was felt that this did not detract from the validity of the study.

GLP compliance:

yes

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

2,4-dichlorophenol

EC Number:

204-429-6

EC Name:

2,4-dichlorophenol

Cas Number:

120-83-2

Molecular formula:

C6H4Cl2O

IUPAC Name:

2,4-dichlorophenol

Details on test material:

- Name of test material (as cited in study report):2,4-Dichlorophenol
- Physical state: solid
-Storage: Sealed containers at ambient temperature.

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Portage, Michigan
- Age at study initiation: Approximately 22 weeks
- Weight at study initiation: 179 -246g
- Fasting period before study: Not specified.
- Housing: During breeding a single female and male were housed in suspended wire -mesh cages. After copulation females were removed from the male’s cages and housed individually in suspended wire-mesh cages.
- Diet (e.g. ad libitum): Purina Certified Rodent Chow #5002 ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: Not specified in the study, however animals were delivered to the testing facility 17th June 1982, the study was initiated on the 24th August 1982.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22.2oC +/- 1.7oC (72oF +/- 3oF)
- Humidity (%): 40%
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 12 hours light/ 12 hours dark
ht at study initiation: 179 -246g
- Fasting period before study: Not specified.
- Housing: During breeding a single female and male were housed in suspended wire -mesh cages. After copulation females were removed from the males cages and housed individually in suspended wire-mesh cages.
- Diet (e.g. ad libitum): Purina Certified Rodent Chow #5002 ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: Not specified in the study, however animals were delivered to the testing facility 17th June 1982, the study was initiated on the 24th August 1982.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22.2oC +/- 1.7oC (72oF +/- 3oF)
- Humidity (%): 40%
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 12 hours lght/ 12 hours dark

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: The test material was warmed to approximately 40oC to allow liquefaction. The liquefied test material was weighed into a volumetric flask and sufficient vehicle added to achieve the correct concentration for each dose group. Test solutions were prepared fresh weekly.

VEHICLE
- Justification for use and choice of vehicle (if other than water): Test substance has low solubility in water.
- Concentration in vehicle: 50.0 mg/ml, 93.75 mg/ml, 187.50 mg/ml
- Amount of vehicle (if gavage): 4 ml/kg

Analytical verification of doses or concentrations:

not specified

Details on mating procedure:

- Impregnation procedure: cohoused
- M/F ratio per cage: 1:1
- Length of cohabitation: until copulation
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy

Duration of treatment / exposure:

Animals were dosed for 10 consecutive days initiating on gestation day 6 and continuing up to and including day 15 of gestation.

Frequency of treatment:

Once daily

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 200, 375, 750 mg/kg/day
Basis:
actual ingested

No. of animals per sex per dose:

34 female rats per dose level

Control animals:

yes, concurrent vehicle

Details on study design:

Doses were selected based on the results from a range finding study.
Range finding study was performed on nine groups of 10 rats at dose levels of 25, 75, 150, 200, 300, 400, 500, 750 and 1000 mg/kg/day.
One female died in the 750 mg/kg/day dose group and seven in the 1000 mg/kg /day dose group.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule:Twice daily
- Cage side observations were summarised in the report.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: gestation days 0, 6, 10, 12, 15 and 20.

BODY WEIGHT: Yes
- Time schedule for examinations: Individually recorded on gestation days 0, 6, 10, 12, 15 and 20.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: Where possible heart, lungs, liver, kidneys and gross lesions.

Ovaries and uterine content:

The ovaries and uterine content were 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

Fetal examinations:

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

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Survival rates at doses of 200 and 375 mg/kg/day were unaffected by the administration of the test substance, however four animals died between days 8 and 12 of gestation in the 750 mg/kg/day dose group. This was considered treatment related.
Dried red material in the facial area, hair loss in the abdominal region and respiratory rattles were observed in the majority of animals at the highest dose level but also infrequently in the 375 mg/kg/day dose group.
Dose related increases in yellow staining and matting of the urogenital hair coat occurred in all treatment groups when compared with the control group. The mean maternal body weight gain was inhibited at all dose levels for the duration of the treatment period, gestation days 6 to 15. The effects were dose related and statistically significant at all levels. This trend continued in all groups for the post-treatment period (days 15-20), the most significant decrease being in the highest dose group.
Gravid uterine weights, corrected body weights and adjusted body weight change values among treated dams were slightly decreased at the highest dose level only.

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
No significant treatment induced effects were observed in the 200 and 375 mg/kg/day treatment groups; however the mean foetal weights were very slightly reduced at 750 mg/kg/day in comparison with the control group.
Survival of the foetuses in the womb was also slightly lower in the 750 mg/kg/day than the control group due to an increase in early embryonic death. The reduced foetal weights and foetus survival may represent a slight degree of embryo toxicity or foetal toxicity in this group but was more likely to be a secondary effect of the excessive maternal toxicity.

No effects attributable to the administration of 2,4 Dichlorophenol were observed regarding the mean numbers of viable foetuses, early or late resorptions, post implantation loss, implantation sites, corpora lutea, foetal crown-rump length, mean foetal body weight or the distribution of foetal sex in the 200 and 375 mg/kg/day test groups.
Corresponding values in the 750mg/kg/day test group were similar to the control group with the following exception:
-A slight increase in the post-implantation loss and an associated decrease in litter size were noted. The effect was mainly due to two dams with a high degree of resorptions, one of the dams having whole litter resorption. Mean foetal weights were reduced in the high dose group. The findings may represent a slight degree of toxicity in the highest dose group. All values obtained at the caesarean section were statistically comparable between all study groups.

Implantation efficiency was slightly reduced in all dose groups in comparison with the control, however since this took place prior to the initiation of dosing it was considered a result of biological variation.

No significant gross internal morphological changes were observed among the dams at the sacrifice which could be considered treatment related.

The occurrence of malformed foetuses (litters containing malformed young) was lower in the 750 mg/kg/day test groups than in the control group, the occurrence was comparable with the control group for the 200 and 375 mg/kg/day test groups.
The numbers/percentages of foetuses and litters with anomalies were not statistically different when compared with the control group at all levels tested.
A statistically significant increase in the number of litters with unossified sternebrae (#1, 2, 3, and/or4) and a significant increase in reduced ossification of vertebral arches occurred in the 750 mg/kg/day group in comparison with the control group. Unossified sternebrae were present in one foetus in each of 4 litters in this group, reduced ossification of vertebral arches was observed in one foetus in 6 different litters. These effects were observed among the lighter foetuses in the 750 mg/kg/day group. The biological significance of unossified sternebrae and reduced ossification of vertebral arches is not well defined and usually occur in the presence of other indicators of retarded foetal development such as reduced foetal weights, as was the case in this study. It should be emphasised that these findings represent developmental variation rather than aberrant morphological development.

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

> 750 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Oral administration of 2,4-Dichlorophenol to pregnant Fischer 344 rats during the period of organogenesis did not produce a teratogenic response at doses of 750 mg/kg/day or less.

Executive summary:

A teratology study was performed to determine the effect of 2,4 Dichlorophenol on Fischer 344 rats. The study was performed in accordance with GLP and OECD 414. A sight deviation was made such that no data was recorded on food consumption, however it was not deemed to have a detrimental effect on the study.

Groups of 34 female rats were exposed to a single daily dose of the test substance in corn oil from day 6 through day 15 of gestation inclusive. Dose levels of 200, 375 and 750 mg/kg/day were administered alongside a control group exposed to the vehicle only.

Throughout the gestation period the animals were observed twice daily for toxicity and weighed on gestation days 0, 6, 10, 12, 15 and 20. On gestation day 20 all surviving females were sacrificed for the scheduled caesarean section: foetuses were weighed, sexed and examined for external, skeletal and soft tissue abnormalities and developmental variations.

Signs of toxicity were present at all levels tested. Body weight gain inhibition occurred in all treatment groups; the effects were statistically significant and dose-related. Clinically 4 animals died in the 750 mg/kg/day group prior to the conclusion of treatment. Additional indicators of maternal toxicity included urogenital staining of the fur at all dose levels and increased incidence of hair loss and respiratory rattles at the 750 mg/kg/day dose level.

A slight increase in the early embryonic deaths was observed in the highest dose group only. Foetal weights were lower in the high dose group than the control group; corresponding reductions in ossification of sternebrae and vertebral arches were also observed.

The reduced foetal weights and survival in the womb may represent a slight degree of embryo toxicity or foetal toxicity but were more likely a secondary effect of the excessive maternal toxicity.

It was concluded that 2,4 -Dichlorophenol was not teratogenic at levels of 750 mg/kg/day and below.

NOAEL : >750mg/kg/day