Chlorimuron ethyl

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

ethyl 2-({[(4-chloro-6-methoxypyrimidin-2-yl)carbamoyl]amino}sulfonyl)benzoate

EC Number:

618-690-2

Cas Number:

90982-32-4

Molecular formula:

C15H15ClN4O6S

IUPAC Name:

ethyl 2-({[(4-chloro-6-methoxypyrimidin-2-yl)carbamoyl]amino}sulfonyl)benzoate

Test material form:

solid

Details on test material:

96% purity

Test animals

Species:

rat

Strain:

other: Crl:CD®(SD)BR

Details on test animals or test system and environmental conditions:

Test animals: Source: Charles River Breeding Laboratories, Inc., Kingston, New York;
Age at study initiation: females were 60 days (nulliparous) and males were 85 days old;
Weight at study initiation: 163.3-191.5 g (females) and 304.3-386.2 g (males);
Housing: Male and female rats were housed singly in stainless steel, wire-mesh cages throughout the study;
Diet: Purina Certified Rodent Chow® 5002, Checkers ad libitum;
Water: Water ad libitum; Acclimation period: 7 Days;
Environmental conditions: Animal room temperature was maintained between 70 and 78°F; Temperatures in the animal rooms rose to between 78 and 80°F for about two hours on one day during the quarantine period; Relative humidity was maintained between 35 and 75% in the animal rooms. Room air changed about 12 times per hour; A light cycle of 12 hours light/12 hours dark (dark period was from 6:00 pm and 6:00 am) was maintained throughout the study

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

other: Methyl cellulose

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The diet feed samples were analyzed by reverse phase liquid chromatography (RPLC). The entire 5 mL methyl cellulose suspension was dissolved in methanol with ultrasonic agitation. Further dilutions with methanol were made to cover the range of the calibration curve. The solution was then filtered and injected into a liquid chromatograph using the following conditions:

Column: Zorbax® ODS 25 cm x 4.1 mm i.d.
Mobile phase: 45% acetonitrile in pH 3 adjuted deionized water
Flow rate: 2 mL/min
Detector: Varian Model UV-50 variable-wavelength ultraviolet set at 254 nm
Sample volume injected: 10 μL
Quantitation: Peak area measurement
Standard solutions: 0.5, 0.9, 1.1 mg/mL test substance
Retention time of the test substance: Approximately 9 minutes

Details on mating procedure:

The females were mated by overnight cohabitation with mature males of the same strain, and mating will be verified each morning by detecting a sperm plug in the vagina or on the cage board (Day 1 of gestation).

Duration of treatment / exposure:

Single gavage administration

Frequency of treatment:

Daily from day 7 to day 16 of gestatyion

Duration of test:

21 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

30 mg/kg bw/day (actual dose received)

Remarks:

The actual dosages administered, calculated as the mean of three test suspension samples at each dose level, was 30 mg//kg/day

Doses / concentrations 2

Dose / conc.:

150 mg/kg bw/day (nominal)

Remarks:

The actual dosages administered, calculated as the mean of three test suspension samples at each dose level, was 152 mg//kg/day

Doses / concentrations 3

Dose / conc.:

600 mg/kg bw/day (nominal)

Remarks:

The actual dosages administered, calculated as the mean of three test suspension samples at each dose level, was 682 mg//kg/day

No. of animals per sex per dose:

25

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

The dams were weighed upon arrival, just before breeding, Days 1G, 6 through 17G and Day 21G. Individual clinical signs were observed upon arrival, before breeding, each morning from Day 1 through 21G and each afternoon from Day 7 through 16G (dosing period). Feed consumption was measured throughout gestation.

Ovaries and uterine content:

The intact and empty uterus of each dam having one or more fetuses will be weighed to calculate actual maternal body weight gain during gestation.
Ovaries were not examined.

Fetal examinations:

Fetal weight was recorded for all live fetuses and those classified as "Dead" fetuses. External alterations were detected and recorded for all live fetuses. Soft tissue alterations were detected and recorded for the first live fetus and thereafter for every other live fetus of each litter; all stunted fetuses and all live fetuses with external malformations also will be examined for soft tissue alterations. Head alterations will be detected and recorded for those fetuses examined for soft tissue alterations. Skeletal alterations will be detected and recorded for all fetuses (including "Dead" fetuses; the fetal heads that were fixed in Bouin's solution will be excluded.

Statistics:

The litter will be used as the experimental unit. The Fisher's exact test will be used to determine significant differences in the incidence of pregnancy, clinical signs, maternal mortality, and of individual fetal alterations when more than 75% ties are present in the data to be analyzed.
Jonckheere's will be used to determine the presence of a dose response. Dunnett's test will be used for testing the significance of differences in feed consumption, in maternal body weight, and body weight gain. For these parameters, a two-way analysis of variance will be used to detect differences among breeding lots and test groups. For all other parameters, the Mann-Whitney U test will be applied .to detect significant differences between the control group and individual experimental groups. Fetal alterations will be listed within groups and presented as the number of affected fetuses per number affected litters but analyzed on the basis of proportion affected within litters for each group by application of the Mann-Whitney U test. The level of significance will be p≤0.05.

Historical control data:

Not included in this report

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

There was no significant difference between the control and experimental groups in the frequency of clinical signs noted when the maternal viscera were examined at sacrifice.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Days 7-21 of gestation

Group Maternal Body Weight

Control 52.1 ± 2.54 g
30 mg/kg 48.6 ± 2.26 g
150 mg/kg 44.0 ± 1.93 g*
600 mg/kg 34.2 ± 2.08 g*

* Significantly different from control value, p≤0.05 (Dunnett's test)

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

In the 600 mg/kg/day group, there was a significant decrease in feed consumption during the treatment period (Days 7-16 of gestation).

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:

no effects observed

Description (incidence and severity):

The mean absolute and relative liver weights were similar between the control and experimental groups.

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Maternal developmental toxicity

Number of abortions:

no effects observed

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

effects observed, non-treatment-related

Early or late resorptions:

not specified

Dead fetuses:

effects observed, non-treatment-related

Description (incidence and severity):

1 dead fetus in the 30 mg/kg/day group; none in the control, 150, or 600 mg/kg/day groups.

Changes in pregnancy duration:

not specified

Description (incidence and severity):

Migrated Data from removed field(s)
Field "Effects on pregnancy duration" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsMaternalAnimals.MaternalDevelopmentalToxicity.EffectsOnPregnancyDuration): no effects observed

Changes in number of pregnant:

no effects observed

Details on maternal toxic effects:

Maternal toxicity at the 600 mg/kg level was demonstrated by a significant (p<0.05) increase in alopecia and significant (p<0.05) decreases in feed consumption and body weight gain during the treatment period (Days 7-16 of gestation). Dams in the 150 mg/kg group also showed a significant (p<0.05) decrease in body weight gain during the treatment period. The adverse effects observed in the 150 and 600 mg/kg groups were dose-related. No adverse effects were detected among dams given 30 mg/kg/day when compared with control dams.

Effect levels (maternal animals)

Dose descriptor:

NOEL

Effect level:

30 mg/kg bw/day (actual dose received)

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Results (fetuses)

Fetal body weight changes:

effects observed, treatment-related

Description (incidence and severity):

Group Fetal Body Weight

Control 3.3 ± 0.04 g
30 mg/kg 3.3 ± 0.07 g
150 mg/kg 3.4 ± 0.06 g
600 mg/kg 3.0 ± 0.16 g*

* Significantly different from control value, p≤0.05 (two-tailed Mann-Whitney U test)
Migrated Data from removed field(s)
Field "Fetal/pup body weight changes" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsFetuses.FetalPupBodyWeightChanges): not examined

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

not specified

Changes in litter size and weights:

no effects observed

Changes in postnatal survival:

not examined

External malformations:

effects observed, treatment-related

Description (incidence and severity):

In the 600 mg/kg/day group, there was a significant (p<0.05) increase in fetal "variations" that included bipartite and. dumbelled centra and partially ossified and unossified sternebrae and centra. Fetal "variations" were also significantly (p<0.05) increased among fetuses from the 150 mg/kg group largely due to an increase in partially ossified and unossified sternebrae. The adverse effects observed in the 150 and 600 mg/kg/day groups were dose-related.

Skeletal malformations:

effects observed, treatment-related

Description (incidence and severity):

A significant increase that was dose-related, in the frequency of "developmental variations" was noted among fetuses from the 600 mg/kg group when compared with the control value. Among the "developmental variations" the incidence of bipartite and dumbelled centra were significantly greater among fetuses in the 600 mg/kg group when compared with the control value. A significant increase that was dose-related, in the frequency of "variations due to retarded development" was noted for fetuses in both the 150 and 600 mg/kg group when compared with the control group. Among the "variations due to retarded development," a significant (p<0.05) increase that was dose-related was observed in the frequency of partially ossified or unossified centra among fetuses in the 600 mg/kg group. In addition, the incidence of partially ossified or unossified sternebra was significantly higher and dose-related for fetuses in both the 150 and 600 mg/kg groups when compared with the control fetuses. When "developmental variations" and "variations due to retarded development" were combined and statistically analyzed, a significant increase in the total number of variations was noted among fetuses in the 600 mg/kg group when compared with the control value. A weak teratogenic response in the 600 mg/kg dose level was demonstrated by a "borderline" dose-related response (p<0.07; Jonckheere's test) in conjunction with an increase (p<0.06; two-tailed Mann-Whitney U test) in the frequency of malformed fetuses per litter. Five malformed fetuses from a dam given 600 mg/kg (this dam was one of the six darns given 802 mg/kg on day 7 of gestation) exhibited subcutaneous hematomas between the distal phalanges and skin, brachydactyly and syndactyly on one or both of the fore and hind paws. This association of malformations has been described by several investigators and has been termed the "edema" syndrome. In addition, an increase in the incidence of rnicrophthalmia was noted when the control group (1 fetus/l litter) was compared with the 600 mg/kg group (10 fetuses/4 litter; one litter had six affected fetuses).

Visceral malformations:

no effects observed

Effect levels (fetuses)

Dose descriptor:

NOEL

Effect level:

30 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

fetal/pup body weight changes

external malformations

Applicant's summary and conclusion

Conclusions:

Maternal and fetal toxicity were demonstrated at the 150 and 600 mg/kg/day test substance dose levels. A weak teratogenic response was detected at 600 mg/kg/day, a dose level that was overtly toxic to the dam. No adverse effects to the dam or conceptus were detected after administering 30 mg/kg/day of the test substance. Thus, in this study, the test substance was not demonstrated to represent a unique hazard to the conceptus.

Executive summary:

Groups of 25 pregnant rats were administered by gavage 0, 30, 150 or 600 mg/kg/day of the test substance in 0.5% methyl cellulose on days 7-16 of gestation. The actual dosages administered, calculated as the mean of three test suspension samples at each dose level, were 0, 30, 152 and 682 mg//kg/day (OECD 414).

                                

Maternal toxicity at the 600 mg/kg level was demonstrated by a significant (p<0.05) increase in alopecia and significant (p<0.05) decreases in feed consumption and body weight gain during the treatment period (Days 7-16 of gestation). Dams in the 150 mg/kg group also showed a significant (p<0.05) decrease in body weight gain during the treatment period. The adverse effects observed in the 150 and 600 mg/kg groups were dose-related. No adverse effects were detected among dams given 30 mg/kg/day when compared with control dams. Fetal toxicity at 600 mg/kg was demonstrated by a significant (p<0.05) decrease in body weight and significant (p<0.05) increase in fetal "variations" that included bipartite and dumbelled centra and partially ossified and unossified sternebrae and centra. Fetal "variations" were also significantly (p<0.05) increased among fetuses from the 150 mg/kg group largely due to an increase in partially ossified and unossified sternebrae. The adverse effects observed in the 150 and 600 mg/kg/day groups were dose-related. A weak teratogenic response for the test substance at the 600 mg/kg dose level was demonstrated by a "borderline" dose-related response (p<0.07) in conjunction with an increase (p<0.06) in the frequency of malformed fetuses/litter. No adverse effects were noted among fetuses from dams given 30 mg/kg/day.