Dichlobenil

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24 March 1988 to 15 August 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1988

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1991

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

18 mated females instead of 20 were used in the study

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPP 83-3 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

18 mated females instead of 20 were used in the study

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Dichlobenil

EC Number:

214-787-5

EC Name:

Dichlobenil

Cas Number:

1194-65-6

Molecular formula:

C7H3Cl2N

IUPAC Name:

2,6-dichlorobenzonitrile

Test material form:

solid: particulate/powder

Test animals

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Weight at study initiation: 3.00-4.48 kg at mating
- Housing: individually in stainless steel cages
- Diet: ad libitum
- Water: mains water ad libitum
- Acclimation period: at least 19 days before mating

ENVIRONMENTAL CONDITIONS
- Temperature: 16-22 °C
- Humidity: 40-70 %
- Air changes: minimum of 15 per hour
- Photoperiod: 14 hours light/10 hours dark

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

other: 1 % gum tragacanth

Details on exposure:

Suspensions of the test material in vehicle were prepared weekly and dispensed as daily aliquots

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples of each test formulation were taken from the first and second weekly preparations for analysis.

Details on mating procedure:

Each female was mated with one proven stud New Zealand White buck.

Duration of treatment / exposure:

To mated females from days 7 to 19 of gestation.

Frequency of treatment:

Once daily

Duration of test:

Animals were killed on day 29 of gestation.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

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

Doses / concentrations 2

Dose / conc.:

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

Doses / concentrations 3

Dose / conc.:

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

No. of animals per sex per dose:

18

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily during gestation

BODY WEIGHT: Yes
- Time schedule for examinations: days 0, 7, 13, 19, 23 and 28 of gestation.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined: days 0-7, 7-13, 13-19, 19-23, and 23-29 of gestation.

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 and intrauterine position of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other: pregnancy status

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:

Levene's test was used to test for equality of variances between groups for body weight gain (except days 7-13), food intake, uterus weight and mean litter weight. Where there was a significant difference between groups using one-way analysis of variance, pairwise t-tests between treated groups and the control were conducted. Where Levene's test was significant (p<0.05), non-parametric tests were performed.

Major and minor external/visceral defects and major skeletal defects were analysed by comparing the proportion of litters in the treated groups with one defect to the proportion in the control group using the Fisher exact test.

Kruskal-Wallis non-parametric analysis of variance was performed on all other parameters. Where there was a significant overall difference between groups (p<0.05), the Wilcoxon Rank Sum Test was performed for each treated group against the controls.

Indices:

Percentage pre-implantation loss = ((no. of corpora lutea - no. of implantation sites) / no. of corpora lutea) x 100

Percentage of post-implantation loss = ((no. of implantation sites - no. of live young) / no. of implantation sites) x 100

Females as % of males = (no. of females / no. of males) x 100

Fertility index = (no. of females pregnant / no. of females mated) x 100

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

no effects observed

Description (incidence and severity):

The clinical condition of surviving animals was generally comparable in all groups.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Four of the treatment animals died or were killed, two in the low dose and one in both the median and high dose groups. The distribution between the treated groups did not indicate an effect of treatment.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Group mean body weight gain of the high dose animals was significantly lower than the controls. The majority of high dose animals lost weight from day 7 to day 13 of gestation. In three animals the loss persisted until treatment ceased. There was no adverse effect of treatment on weight gain at the low or intermediate dose level.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Food intake of high dose animals was significantly lower than controls over the treatment period. No significant differences were observed at the low and intermediate dose levels.

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):

Necropsy revealed no treatment-related lesions.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

Necropsy revealed no treatment-related lesions.

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Maternal developmental toxicity

Number of abortions:

not examined

Pre- and post-implantation loss:

effects observed, treatment-related

Description (incidence and severity):

The number of corpora lutea and implantations per dose were comparable in all groups. Pre-implantation loss was within the expected range in all groups. Post-implantation loss was higher than controls in the high dose group. The increase was mainly attributable to two atypical litters (number 66 and 72) and was not statistically significant. The number of foetuses per litter was correspondingly reduced. The incidence of intrauterine deaths in the low and intermediate dose groups was lower than controls and litter size was marginally increased.

Total litter losses by resorption:

not examined

Early or late resorptions:

not examined

Dead fetuses:

not examined

Changes in pregnancy duration:

no effects observed

Description (incidence and severity):

The number of pregnant animals surviving to day 29 of gestation was between 14 and 16 in every group.

Changes in number of pregnant:

no effects observed

Description (incidence and severity):

Pregnancy incidence was 100 % in the low dose and 94.4 % in all other groups.

Other effects:

not examined

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

45 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Fetal body weight changes:

effects observed, treatment-related

Description (incidence and severity):

Foetal weight was lower than controls in the high dose group. The reduction was not statistically significant and was attributable to three atypical litters (number 66, 71, and 72). There was no adverse effect on foetal weight in the low and intermediate dose groups.

Reduction in number of live offspring:

not examined

Changes in sex ratio:

not examined

Changes in litter size and weights:

not examined

Changes in postnatal survival:

not examined

External malformations:

effects observed, treatment-related

Description (incidence and severity):

The incidence of litters containing foetuses showing major defects was significantly higher than controls in the high dose group. Again the increase was mainly attributed to litters 66, 71, and 72 suggesting that these were mediated by maternal toxicity. There was no adverse effect of treatment on the incidence of major defects in the low or intermediate dose groups. The incidence of minor defects or variations did not indicate an effect of treatment at any of the dose levels investigated.

Skeletal malformations:

not specified

Visceral malformations:

not specified

Other effects:

not examined

Effect levels (fetuses)

1

Key result

Dose descriptor:

NOAEL

Effect level:

45 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: embryotoxicity

2

Key result

Dose descriptor:

NOAEL

Effect level:

45 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: fetotoxicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Table 1: Mean weight (kg), body weight gain (kg) and food intake (g)

		Dose group (mg/kg bw/day)
Day	Parameter	0	15	45	135
0	Body weight	3.63	3.61	3.76	3.68
7	Body weight	3.78	3.77	3.91	3.84
	Body weight gain	0.15	0.16	0.15	0.16
	Food intake	201	204	212	212
13	Body weight	3.83	3.84	3.97	3.70***
	Body weight gain	0.05	0.07	0.06	-0.14
	Food intake	175	184	184	115***
19	Body weight	3.94	3.97	4.08	3.80
	Body weight gain	0.11	0.13	0.11	0.10
	Food intake	168	171	170	124*
23	Body weight	4.03	4.0	4.16	3.85
	Body weight gain	0.09	0.04	0.08	0.05
	Food intake	148	141	158	132
29	Body weight	4.16	4.03**	4.23	4.00
	Body weight gain	0.13	0.02	0.07	0.15
	Adjusted body weight	3.58	3.48	3.68	3.51
	Food intake	127	92	118	122
Total mean	Body weight gain	0.53	0.42	0.47	0.32
	Food intake	166	161	171	144

*P<0.05; ***P<0.001

Table 2: Group incidence of foetuses with defects

		Dose group (mg/kg bw/day)
Observation		0	15	45	135
Number of foetuses examined		142	154	146	115
External and visceral effects	Major	0	1	1	11**
	Minor	5	14	2	12
	Variants	46	47	70	39
Skeletal	Major	1	0	0	24
	Minor	33	45	36	16
	Variants	128	141	130	106
Total number of foetuses showing major defects		1	1	1	26

** P<0.01

Applicant's summary and conclusion

Conclusions:

Under the conditions of the test, administration of the test material at 135 mg/kg bw/day elicited maternal toxicity, characterised by maternal weight loss at the onset of dosing and reduced food intake over the treatment period. In three animals, the reaction was so severe as to elicit corresponding foetal effects. The litters of these animals showed reduced foetal weight and an increased incidence of intrauterine deaths and major abnormalities. In the remaining litters, the incidence of foetal effects did not greatly differ from normal values. There was no adverse effect of treatment, maternal or foetal, at 15 or 45 mg/kg/day in either this or the previous study (Barker, 1989b). The NOAEL for both maternal and embryo/foetotoxicity in this study is 45 mg/kg bw/day.

Executive summary:

In a GLP compliant study conducted in line with standardised guidelines OECD 414 and EPA OPP 83-3, the effect of the test material on developmental toxicity was determined in the rabbit.

Rabbits were administered the test material by oral (gavage) at 0, 15, 45 and 135 mg/kg bw/day. Administration of the test material at 35 mg/kg bw/day elicited maternal toxicity, characterised by maternal weight loss at the onset of dosing and reduced food intake over the treatment period. In three animals, the reaction was so severe as to elicit corresponding foetal effects. The litters of these animals showed reduced foetal weight and an increased incidence of intrauterine deaths and major abnormalities. In the remaining litters, the incidence of foetal effects did not greatly differ from normal values. There was no adverse effect of treatment, maternal or foetal, at 15 or 45 mg/kg/day in either this or the previous study (Barker, 1989b).

The NOAEL for both maternal and embryo/foetotoxicity in this study is 45 mg/kg bw/day.