Fenuron

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

A reproductive and developmental toxicity study with Fenuron was conducted in 5 groups of rats dosed by oral gavage at 0, 20, 38, 75 and 1500 mg/kg bw/d. In a first publication the reproductive and developmental toxicity was investigated. Fenuron dosed at 75 and 1500 mg/kg bw/d resulted in increased prenatal mortality of the fetuses, reduced fertility, inhibited development of embryos and circulatory disorders. At 38 mg/kg bw/d, less pronounced changes were observed, and the dose of 20 mg/kg did not cause any effects in the experimental animals and was considered reproductive/developmental NOAEL. In a separate publication, the organs of the pregnant rats and embryos were subject to histological examination. Parental toxicity was demonstrated by circulatory disorders, manifested by vascular expansion and hyperemia, edema, and sometimes small hemorrhages. In the foetuses at the same doses, these changes were more significant – the edemas were diffuse, and the hemorrhages were abundant. The obtained results indicate the effect of Fenuron on the blood flow and permeability of the vascular walls, resulting in parental (maternal) and secondary fetal toxicity. The dose of 20 mg/kg bw/d was also a parental NOAEL.

Link to relevant study records

Reference

Reference 1

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1989

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: in accordance with a complex scheme developed by V.A. Gofmekler et al. described in “Methods of studying long-term effects of chemical air pollution: Experimental and in-situ study of embryotropic effects and influence on the female organism during pregnancy / Gofmekler, V.A., Krasovitskaya, M.M., Sheparev, A.A. et al. Methodological instructions. – Vladivostok, 1978.”
- Short description of test conditions:
4 groups of female albino rats with 15 animals / group were treated with the study preparation administered intragastrically in the doses of 1/5, 1/100, 1/200, and 1/400 LD50 from the 6th to the 15th day of pregnancy. A fith control group was only treated with starch.
- Parameters analysed / observed:
The organs of the pregnant rats and embryos were subject to histological examination.

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

other: albino

Sex:

female

Route of administration:

oral: gavage

Duration of treatment / exposure:

from the 6th to the 15th day of pregnancy

Dose / conc.:

1 500 mg/kg bw/day (actual dose received)

Remarks:

1/5 LD50

Dose / conc.:

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

Remarks:

1/100 LD50

Dose / conc.:

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

Remarks:

1/200 LD50

Dose / conc.:

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

Remarks:

1/400 LD50

No. of animals per sex per dose:

15

Control animals:

yes, sham-exposed

Postmortem examinations (parental animals):

The organs of the pregnant rats and embryos were subject to histological examination. The material was preserved in a 10% neutral formalin solution, and paraffin sections of the rat organs and transverse sections of the fetuses were stained with hematoxylin and eosin.
This article presents the results of the histological examination of the ovaries, placenta, brain, oesophagus, stomach, and heart of the pregnant rats which were treated with various doses of fenuron, administered intragastrically, with histotopograms of their fetuses provided as well.

Postmortem examinations (offspring):

The organs of the embryos were subject to histological examination. The material was preserved in a 10% neutral formalin solution, and paraffin transverse sections of the fetuses were stained with hematoxylin and eosin.
This article presents the results of the histological examination of the ovaries, placenta, brain, oesophagus, stomach, and heart of the pregnant rats which were treated with various doses of fenuron, administered intragastrically, with histotopograms of their fetuses provided as well.

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

Food efficiency:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

The results of the histological examination of the organs of the rats that received 1/5 LD50 of fenuron (1500 mg/kg) (and of their fetuses) contained pathological changes.
The oesophagus and stomach walls, heart and brain of the rats had signs of hemodynamic abnormalities and dystrophic changes. The vessels of the brain tunics and brain substance were expanded and hyperemic; moderate perivascular edema was detected. The nerve cells of the cortex and the brainstem nuclei were in a swollen state. The mucous membrane of the stomach and oesophagus was edematous and hyperemic. The heart had cloudy swelling and uneven colouring of the myocardiocytes, sudden expansion and hyperemia of the epicardium and myocardium vessels. The cortical layer of the ovaries contained massive yellow bodies, primordial and growing follicles, and numerous atretic bodies. In the placenta, acute vascular hyperemia, single small perivascular hemorrhages, and chorion edema were observed. The layers of decidual cells penetrated deeply into the myometrium with edematous and hyperemic stroma.
With the dose of fenuron reduced to 75 mg/kg (1/100 LD50), the response of the pregnant females to the effect of the toxic agent decreased. The revealed hemodynamic abnormalities in the stomach and oesophagus walls, myocardium, and brain are significantly weaker than in the females that received the preparation in the dose of 1500 mg/kg
The effect of fenuron in the dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain.
When the herbicide was administered in the dose of 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.
Thus, in the examined organs of pregnant rats, circulatory disorders, manifested by vascular expansion and hyperemia, edemas, and sometimes small hemorrhages, prevailed.
The obtained results indicate the effect of fenuron on the blood flow and permeability of the vascular walls.

Histopathological findings: neoplastic:

not examined

Reproductive function: oestrous cycle:

not specified

Reproductive function: sperm measures:

not examined

Reproductive performance:

effects observed, treatment-related

Description (incidence and severity):

At the dose level of 1500 mg/kg bw, the cortical layer of the ovaries contained massive yellow bodies, primordial and growing follicles, and numerous atretic bodies. In the placenta, acute vascular hyperemia, single small perivascular hemorrhages, and chorion edema were observed. The layers of decidual cells penetrated deeply into the myometrium with edematous and hyperemic stroma.
With the dose of fenuron reduced to 75 mg/kg (1/100 LD50), the response of the pregnant females to the effect of the toxic agent decreased.
The effect of fenuron in the dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain.
When dosed at 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.

Dose descriptor:

NOAEL

Effect level:

20 mg/kg bw/day

Based on:

test mat.

Sex:

female

Basis for effect level:

histopathology: non-neoplastic

Critical effects observed:

yes

Lowest effective dose / conc.:

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

System:

cardiovascular

Treatment related:

yes

Dose response relationship:

yes

Clinical signs:

not specified

Mortality / viability:

not specified

Body weight and weight changes:

not specified

Food efficiency:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Sexual maturation:

not specified

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Histopathological findings:

effects observed, treatment-related

Description (incidence and severity):

The results of the histological examination of the organs of the rats that received 1/5 LD50 of fenuron (1500 mg/kg) (and of their fetuses) contained pathological changes.
The oesophagus and stomach walls, heart and brain of the rats had signs of hemodynamic abnormalities and dystrophic changes. The vessels of the brain tunics and brain substance were expanded and hyperemic; moderate perivascular edema was detected. The nerve cells of the cortex and the brainstem nuclei were in a swollen state. The mucous membrane of the stomach and oesophagus was edematous and hyperemic. The heart had cloudy swelling and uneven colouring of the myocardiocytes, sudden expansion and hyperemia of the epicardium and myocardium vessels. The cortical layer of the ovaries contained massive yellow bodies, primordial and growing follicles, and numerous atretic bodies. In the placenta, acute vascular hyperemia, single small perivascular hemorrhages, and chorion edema were observed. The layers of decidual cells penetrated deeply into the myometrium with edematous and hyperemic stroma.
With the dose of fenuron reduced to 75 mg/kg (1/100 LD50), the response of the pregnant females to the effect of the toxic agent decreased. The revealed hemodynamic abnormalities in the stomach and oesophagus walls, myocardium, and brain are significantly weaker than in the females that received the preparation in the dose of 1500 mg/kg
The effect of fenuron in the dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain.
When the herbicide was administered in the dose of 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.
Thus, in the examined organs of pregnant rats, circulatory disorders, manifested by vascular expansion and hyperemia, edemas, and sometimes small hemorrhages, prevailed.
The obtained results indicate the effect of fenuron on the blood flow and permeability of the vascular walls.

Behaviour (functional findings):

not specified

Developmental immunotoxicity:

not specified

At the dose level of 1500 mg/kg bw, the cortical layer of the ovaries contained massive yellow bodies, primordial and growing follicles, and numerous atretic bodies. In the placenta, acute vascular hyperemia, single small perivascular hemorrhages, and chorion edema were observed. The layers of decidual cells penetrated deeply into the myometrium with edematous and hyperemic stroma.
With the dose of fenuron reduced to 75 mg/kg (1/100 LD50), the response of the pregnant females to the effect of the toxic agent decreased.
The effect of fenuron in the dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain.
When dosed at 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

20 mg/kg bw/day

Based on:

test mat.

Sex:

female

Basis for effect level:

histopathology: non-neoplastic

Critical effects observed:

yes

Lowest effective dose / conc.:

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

System:

cardiovascular

Treatment related:

yes

Dose response relationship:

yes

Reproductive effects observed:

yes

Lowest effective dose / conc.:

38 mg/kg bw/day

Treatment related:

yes

Relation to other toxic effects:

reproductive effects as a secondary non-specific consequence of other toxic effects

Dose response relationship:

yes

Relevant for humans:

not specified

Conclusions:

The effect of fenuron in the dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain.
When the herbicide was administered in the dose of 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.

Executive summary:

The studies were carried out in in 4 groups of female white rats with 15 animals in each group. The fifth group served as a control group. The tested animals were treated with the study preparation administered intragastrically in the doses of 1/5, 1/100, 1/300200, and 1/400 LD50 from the 6th to the 15th day of pregnancy. The control group was only treated with starch.

The organs of the pregnant rats and embryos were subject to histological examination. The material was preserved in a 10% neutral formalin solution, and paraffin sections of the rat organs and transverse sections of the fetuses were stained with hematoxylin and eosin.

This article presents the results of the histological examination of the ovaries, placenta, brain, oesophagus, stomach, and heart of the pregnant rats which were treated with various doses of fenuron, administered intragastrically, with histotopograms of their fetuses provided as well.

The results of the histological examination of the organs of the rats that received 1/5 LD50 of fenuron (1500 mg/kg) and of their fetuses contained pathological changes.

The oesophagus and stomach walls, heart and brain of the rats had signs of hemodynamic abnormalities and dystrophic changes. The vessels of the brain tunics and brain substance were expanded and hyperemic; moderate perivascular edema was detected. The nerve cells of the cortex and the brainstem nuclei were in a swollen state. The mucous membrane of the stomach and oesophagus was edematous and hyperemic. The heart had cloudy swelling and uneven colouring of the myocardiocytes, sudden expansion and hyperemia of the epicardium and myocardium vessels. The cortical layer of the ovaries contained massive yellow bodies, primordial and growing follicles, and numerous atretic bodies. In the placenta, acute vascular hyperemia, single small perivascular hemorrhages, and chorion edema were observed. The layers of decidual cells penetrated deeply into the myometrium with edematous and hyperemic stroma.

With the dose of fenuron reduced to 75 mg/kg (1/100 LD50), the response of the pregnant females to the effect of the toxic agent decreased. The revealed hemodynamic abnormalities in the stomach and oesophagus walls, myocardium, and brain are significantly weaker than in the females that received the preparation in the dose of 1500 mg/kg

The effect of fenuron in the dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain.

When the herbicide was administered in the dose of 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.

Thus, in the examined organs of pregnant rats, circulatory disorders, manifested by vascular expansion and hyperemia, edemas, and sometimes small hemorrhages, prevailed. In the fetuses, these changes were more significant – the edemas were diffuse, and the hemorrhages were abundant. The obtained results indicate the effect of fenuron on the blood flow and permeability of the vascular walls, which was more pronounced in the fetuses.

In the course of examination of the histotopograms of fetuses obtained from these females, the following changes were established: edema of the fibrous connective tissue of the mediastinum and subcutaneous tissue, organ stroma, and acute hyperemia of the vessels of the brain, body, and all the internal organs; extensive hemorrhages in the liver tissue, mediastinum, spinal cord membranes, pleural and abdominal cavities, subcutaneous tissue, back muscles, as well as a developmental lag in one of the paired organs (cerebral hemispheres, eyes, kidneys).

The organs and tissues of the fetuses obtained from the white female rats, the pregnancies of which occurred against the background of intragastric administration of fenuron in the dose of 75 mg/kg (1/100 LD50), were characterized by edema, vascular hyperemia, and multiple extensive hemorrhages in the liver, spinal cord membranes, pleural cavity, and subcutaneous fatty tissue.

When the herbicide was administered in the dose of 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.

Thus, in the examined organs of pregnant rats, circulatory disorders, manifested by vascular expansion and hyperemia, edemas, and sometimes small hemorrhages, prevailed. In the fetuses, these changes were more significant – the edemas were diffuse, and the hemorrhages were abundant. The obtained results indicate the effect of fenuron on the blood flow and permeability of the vascular walls, which was more pronounced in the fetuses.

When administered in the doses of 1500 and 75 mg/kg, fenuron had significant embryotoxic and teratogenic effects. In the dose of 38 mg/kg, the changes caused by the preparation were less pronounced.

Reference 2

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

no guideline followed

Principles of method if other than guideline:

- Principle of test: The studies were carried out according to the complex scheme developed by V.A. Gofmekler et al.
- Short description of test conditions: The studies were carried out , in 4 groups of female white rats with 15 animals in each group. The fifth group served as a control group. 75 female white rats, 544 embryos and 56 rat pups were used in the experiment. The tested animals were treated with the herbicide administered per os using an intra-gastric tube in the doses of 1,500 mg/kg (1/5 LD50); 75 mg/kg (1/100 LD50); 38 mg/kg (1/200 LD50); 20 mg/kg (1/400 LD50).
- Parameters analysed / observed: The evaluation was performed on the 20th day of pregnancy in white rats. The number of corpora lutea in the ovaries, post-implantation mortality of embryos, total fetal embryonic mortality, mass and size of embryos, the number of live and dead embryos, external and internal development anomalies, pathomorphological changes in the organs of females and fetuses were used as the criteria for the evaluation of the embryotoxic effect of phenuron. When evaluating post-implantation mortality of embryos, the number of fetuses, the number of dead and resorbed fetuses, the difference between the presence of yellow bodies and live embryos was counted. The fetuses, which were retrieved from the uterus, were examined under a magnifying glass to identify any external developmental anomalies.
The condition of internal organs was examined by means of serial sectioning (Wilson's method modified by A.P. Dyban), and the condition of the skeleton was evaluated by means of studying total preparations of fetuses stained with alizarin (Dawson's method modified at the Department of Embryology of the N.F. Gamaleya Research Institute of Epidemiology and Microbiology). The reliability of obtained data was assessed using Student's t-distribution method

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

other: albino

Sex:

female

Route of administration:

oral: gavage

Vehicle:

not specified

Duration of treatment / exposure:

from the 6th to the 15th day of pregnancy

Details on study schedule:

Examinations were performed on maternal animals, their fetuses retrieved from their uterus (on the 20th day of pregancy) and their pups.

Dose / conc.:

1 500 mg/kg bw/day (actual dose received)

Remarks:

1/5 LD50

Dose / conc.:

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

Remarks:

1/100 LD50

Dose / conc.:

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

Remarks:

1/200 LD50

Dose / conc.:

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

Remarks:

1/400 LD50

No. of animals per sex per dose:

dosing of 15 pregnant females per dose group
75 female white rats, 544 embryos and 56 rat pups were used in the experiment

Control animals:

yes

Details on study design:

- Dose selection rationale:
In real conditions, the exposure to the herbicide per os is most likely, since the substance under study is not characterized by high volatility and the possibility of its inhalation is virtually ruled out. The minimum doses were selected proceeding from the level of possible environmental contamination. However, exposure of a warm-blooded organism to small doses might not alter its reproductive function. Therefore, studies with large doses of the studied herbicide were also carried out. Phenuron was administered from the 6th to the 15th day of pregnancy, that is, during the main periods of embryogenesis (placentation and organogenesis).

Parental animals: Observations and examinations:

not specified

Litter observations:

PARAMETERS EXAMINED FETUSES
The following parameters were examined in F1 offspring (fetuses retrieved from uterus on the 20th day of pregancy ):
other: total fetal embryonic mortality, mass and size of embryos, the number of live and dead embryos, external and internal development anomalies, pathomorphological changes in the organs of fetuses

GROSS EXAMINATION OF FETUSES:
The fetuses, which were retrieved from the uterus, were examined under a magnifying glass to identify any external developmental anomalies.

OTHER:
The condition of the skeleton was evaluated by means of studying total preparations of fetuses stained with alizarin (Dawson's method modified at the Department of Embryology of the N.F. Gamaleya Research Institute of Epidemiology and Microbiology). STANDARDISATION OF LITTERS


PARAMETERS EXAMINED PUPS
The following parameters were examined in F1 offspring (pups): postnatal development such as mass, eye opening and ear unfolding
Functional loads were applied (swimming, hanging on a horizontal rod) at the end of the second month from the moment of birth of the pups in order to reveal any possible hidden disorders in the body of the offspring of the first litter.

GROSS EXAMINATION OF DEAD PUPS: not specified

Postmortem examinations (parental animals):

SACRIFICE
- Maternal animals: on the 20th day of pregnancy.

GROSS NECROPSY
The condition of internal organs was examined by means of serial sectioning (Wilson's method modified by A.P. Dyban)
Pathomorphological changes in the organs of females were examined.

HISTOPATHOLOGY / ORGAN WEIGHTS
The condition of internal organs was examined by means of serial sectioning (Wilson's method modified by A.P. Dyban)
Pathomorphological changes in the organs of females were examined.

Postmortem examinations (offspring):

SACRIFICE
- The F1 fetuses which were retrieved from the uterus on the 20th day of pregnancy of the maternal animals
- These animals were subjected to postmortem examinations (macroscopic and/or microscopic examination) as follows: The fetuses were examined under a magnifying glass to identify any external developmental anomalies. The condition of internal organs was examined by means of serial sectioning (Wilson's method modified by A.P. Dyban), and the condition of the skeleton was evaluated by means of studying total preparations of fetuses stained with alizarin (Dawson's method modified at the Department of Embryology of the N.F. Gamaleya Research Institute of Epidemiology and Microbiology).

GROSS NECROPSY
- Gross necropsy consisted of external examinations

HISTOPATHOLOGY / ORGAN WEIGTHS
The condition of internal organs was examined by means of serial sectioning (Wilson's method modified by A.P. Dyban), and the condition of the skeleton was evaluated by means of studying total preparations of fetuses stained with alizarin (Dawson's method modified at the Department of Embryology of the N.F. Gamaleya Research Institute of Epidemiology and Microbiology).

Statistics:

The reliability of obtained data was assessed using Student's t-distribution method.

Reproductive indices:

number of corpora lutea in the ovaries
post-implantation mortality of embryos (When evaluating post-implantation mortality of embryos, the number of fetuses, the number of dead and resorbed fetuses, the difference between the presence of yellow bodies and live embryos was counted.)

Offspring viability indices:

total fetal embryonic mortality
post-implantation mortality of embryos
the number of live and dead embryos

Clinical signs:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

1500 mg/kg: The morphological evaluation of internal organs and tissues of female white rats and their fetuses revealed the development of pathological changes. Signs of circulatory disorders and swelling of the tissue were observed in stomach and oesophagus walls, myocardium, and brain. The ovaries did not have any structural deviations, large yellow bodies predominated among the structural elements in terms of volume. The vessels were significantly expanded and hyperemic, there were moderate perivascular hemorrhages in the tissue surrounding the ovaries and in the placenta.
With the dose of phenuron reduced to 75 mg/kg (1/100 LD50), the response of the animals to the effect of the toxic agent has decreased.
The results of histological examination of organs and tissues of animals of the second group were similar to the pathological changes revealed in rats of the first group, while the intensity of these changes was significantly lower.

Reproductive performance:

effects observed, treatment-related

Description (incidence and severity):

Females of the first group(1500 mg/kg) gave birth to 17% less pups as compared to the animals of the third and the fourth groups and the control group, which is obviously related to the prenatal mortality of embryos.
With the dose of phenuron reduced to 75 mg/kg (1/100 LD50), the response of the animals to the effect of the toxic agent has decreased. Meanwhile, the average weight of the embryos and the size of the placenta were lower than in the control group, and the total embryonic and post-implantation mortality of the fetuses also increased (P ≤ 0.05).
The effect of phenuron at a dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient.

Key result

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

female

Basis for effect level:

reproductive performance

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

PUPS: It was discovered that the pups born from the females from the first group (1500 mg/kg) remained afloat 26% less than the animals of the remaining groups and the control group (P ≤ 0.05). The test involving hanging on a horizontal rod did not reveal any difference between the studied indicators in experimental and control animals. When studying offspring born from females of the second group (75 mg/kg), no differences between the animals of the experimental and control groups were revealed in terms of all studied indicators. The exception was the result of functional test (swimming). The floating time was 32% shorter than in the control group (P ≤ 0.05).

Mortality / viability:

mortality observed, treatment-related

Description (incidence and severity):

FETUSES: The studies have shown that the intragastric administration of phenuron at a dose of 1500 mg/kg (1/5 LD50) had an adverse effect on the majority of the studied experimental parameters. Thus, an increase in the total embryonic and post-implantation mortality of fetuses was observed (P ≤ 0.05). With the dose of phenuron reduced to 75 mg/kg (1/100 LD50), the total embryonic and post-implantation mortality of the fetuses also increased (P ≤ 0.05).

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

FETUSES:The studies have shown that the intragastric administration of phenuron at a dose of 1500 mg/kg (1/5 LD50) had an adverse effect on the majority of the studied experimental parameters. The studies have revealed underdevelopment of embryos, which resulted in a decrease of their mass and craniocaudal dimensions.
With the dose of phenuron reduced to 75 mg/kg (1/100 LD50), the average weight of the embryos and the size of the placenta were lower than in the control group.
PUPS: When observing the postnatal development of the offspring (pups), no differences between the animals of experimental and control groups were revealed in such standard criteria as mass, eye opening and ear unfolding.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Macroscopic examination of sections of internal organs (at a dose of 1500 mg/kg) revealed hyperemia of internal organs (19%), pinpoint hemorrhages in the brain (11%), liver (7%) and diaphragm (5%), enlargement of brain ventricles (5%) and renal pelvis (6%).
With the dose of phenuron reduced to 75 mg/kg (1/100 LD50),the macroscopic examination of the internal organs of the fetuses uncovered single cases of hemorrhages in the liver and brain and revealed dilatation of the renal pelvis. 4% of the embryos in the second group exhibited insufficient calcification of the base of skull.

Histopathological findings:

effects observed, treatment-related

Description (incidence and severity):

1500 mg/kg:
FETUSES: The overwhelming majority of fetuses did not exhibit any alterations in the formation of bones and the osseous-articular apparatus. The exception was 6% of embryos, in which insufficient calcification of the base of skull was revealed. The study of embryos revealed moderate edema of the fibrous connective tissue of the mediastinum and subcutaneous tissue, stroma of the organs and acute hyperemia of all vessels of the brain, body and internal organs. The organs and tissues of the fetuses were characterized by multiple extensive hemorrhages in the liver, mediastinum, spinal cord membranes, pleural cavity and subcutaneous tissue. Developmental lag in one of the paired organs (cerebral hemispheres, eyes, kidneys) was also observed.
The results of histological examination of organs and tissues of fetuses of the second group (75 mg/kg)were similar to the pathological changes revealed in fetuses of the first group, while the intensity of these changes was significantly lower.
The effect of phenuron at a dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient. All other tests conducted during the experiment did not reveal any other changes.
The administration of phenuron at a dose of 20 mg/kg (1/400 LD50) was not accompanied by any statistically significant change in the absolute majority of indicators characterizing the embryotropic effect of the studied herbicide.

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

20 mg/kg bw/day

Based on:

test mat. (total fraction)

Sex:

female

Basis for effect level:

viability

Reproductive effects observed:

yes

Lowest effective dose / conc.:

38 mg/kg bw/day

Treatment related:

yes

Relation to other toxic effects:

reproductive effects as a secondary non-specific consequence of other toxic effects

Dose response relationship:

yes

Relevant for humans:

not specified

Conclusions:

It was established that the doses of 1500 mg/kg and 75 mg/kg affected the reproductive function of experimental animals; the dose of 38 mg/kg was of minimum effect while that of 20 mg/kg was of no effect.

Executive summary:

The studies were carried out according to the complex scheme developed by V.A. Gofmekler et al., in 4 groups of female white rats with 15 animals in each group. The fifth group served as a control group. 75 female white rats, 544 embryos and 56 rat pups were used in the experiment. The tested animals were treated with the herbicide administered per os using an intra-gastric tube in the doses of 1500 mg/kg (1/5 LD50); 75 mg/kg (1/100 LD50); 38 mg/kg (1/200 LD50); 20 mg/kg (1/400 LD50).

The evaluation was performed on the 20th day of pregnancy in white rats. The number of yellow bodies in the ovaries, post-implantation mortality of embryos, total fetal embryonic mortality, mass and size of embryos, the number of live and dead embryos, external and internal development anomalies, pathomorphological changes in the organs of females and fetuses were used as the criteria for the evaluation of the embryotoxic effect of phenuron. When evaluating post-implantation mortality of embryos, the number of fetuses, the number of dead and resorbed fetuses, the difference between the presence of yellow bodies and live embryos was counted. The fetuses, which were retrieved from the uterus, were examined under a magnifying glass to identify any external developmental anomalies.
The condition of internal organs was examined by means of serial sectioning (Wilson's method modified by A.P. Dyban), and the condition of the skeleton was evaluated by means of studying total preparations of fetuses stained with alizarin (Dawson's method modified at the Department of Embryology of the N.F. Gamaleya Research Institute of Epidemiology and Microbiology). The reliability of obtained data was assessed using Student's t-distribution method.

The studies have shown that the intragastric administration of phenuron at a dose of 1500 mg/kg (1/5 LD50) had an adverse effect on the majority of the studied experimental parameters. Thus, an increase in the total embryonic and post-implantation mortality of fetuses was observed (P ≤ 0.05). The studies have also revealed underdevelopment of embryos, which resulted in a decrease of their mass and craniocaudal dimensions. Macroscopic examination of sections of internal organs (at a dose of 1500 mg/kg) revealed hyperemia of internal organs (19%), pinpoint hemorrhages in the brain (11%), liver (7%) and diaphragm (5%), enlargement of brain ventricles (5%) and renal pelvis (6%). The overwhelming majority of fetuses did not exhibit any alterations in the formation of bones and the osseous-articular apparatus. The exception was 6% of embryos, in which insufficient calcification of the base of skull was revealed. When observing the postnatal development of the offspring, no differences between the animals of experimental and control groups were revealed in such standard criteria as mass, eye opening and ear unfolding. However, females of the first group gave birth to 17% less pups as compared to the animals of the third and the fourth groups and the control group, which is obviously related to the prenatal mortality of embryos. Functional loads were applied (swimming, hanging on a horizontal rod) at the end of the second month from the moment of birth of the pups in order to reveal any possible hidden disorders in the body of the offspring of the first litter. It was discovered that the pups born from the females from the first group remained afloat 26% less than the animals of the remaining groups and the control group (P ≤ 0.05). The test involving hanging on a horizontal rod did not reveal any difference between the studied indicators in experimental and control animals. The morphological evaluation of internal organs and tissues of female white rats and their fetuses revealed the development of pathological changes. Signs of circulatory disorders and swelling of the tissue were observed in stomach and oesophagus walls, myocardium, and brain. The ovaries did not have any structural deviations, large yellow bodies predominated among the structural elements in terms of volume. The vessels were significantly expanded and hyperemic, there were moderate perivascular hemorrhages in the tissue surrounding the ovaries and in the placenta. The study of embryos revealed moderate edema of the fibrous connective tissue of the mediastinum and subcutaneous tissue, stroma of the organs and acute hyperemia of all vessels of the brain, body and internal organs. The organs and tissues of the fetuses were characterized by multiple extensive hemorrhages in the liver, mediastinum, spinal cord membranes, pleural cavity and subcutaneous tissue. Developmental lag in one of the paired organs (cerebral hemispheres, eyes, kidneys) was also observed.

With the dose of phenuron reduced to 75 mg/kg (1/100 LD50), the response of the animals to the effect of the toxic agent has decreased. Meanwhile, the average weight of the embryos and the size of the placenta were lower than in the control group, and the total embryonic and post-implantation mortality of the fetuses also increased (P ≤ 0.05). The macroscopic examination of the internal organs of the fetuses uncovered single cases of hemorrhages in the liver and brain and revealed dilatation of the renal pelvis. 4% of the embryos in the second group exhibited insufficient calcification of the base of skull. When studying offspring born from females of the second group, no differences between the animals of the experimental and control groups were revealed in terms of all studied indicators. The exception was the result of functional test (swimming). The floating time was 32% shorter than in the control group (P ≤ 0.05). The results of histological examination of organs and tissues of animals and fetuses of the second group were similar to the pathological changes revealed in rats and fetuses of the first group, while the intensity of these changes was significantly lower.

The effect of phenuron at a dose of 38 mg/kg (1/200 LD50) on the reproductive function of white female rats was characterized by an increase of the placental-fetal coefficient. All other tests conducted during the experiment did not reveal any other changes.

The administration of phenuron at a dose of 20 mg/kg (1/400 LD50) was not accompanied by any statistically significant change in the absolute majority of indicators characterizing the embryotropic effect of the studied herbicide.       

The following conclusion can be made based on the analysis of the results obtained in the study of the embryotropic action of phenuron: when administered in the doses of 1500 mg/kg and 75 mg/kg, it increases prenatal mortality of the fetuses, reduces fertility, inhibits the development of embryos and leads to circulatory disorders. When administered to pregnant rats of the third group at a dose of 38 mg/kg, less pronounced changes were observed, and the dose of 20 mg/kg did not cause any embryotropic effects in the experimental animals. Consequently, the doses of 1500 mg/kg and 75 mg/kg can be considered as affecting the reproductive function in white rats, 38 mg/kg – as minimally affecting, and 20 mg/kg – as not affecting. The conducted experimental studies have made it possible to establish a relationship between the embryotoxic and general toxic effect of the studied herbicide. The threshold of general toxic effect of phenuron, established at the level of 300 mg/kg, is eight times greater than the threshold for its adverse reproductive effects. This indicates a greater risk of contact even with minimal amounts of the studied pesticide during pregnancy.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

20 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

Reliable

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

A reproductive and developmental toxicity study with Fenuron was conducted in 5 groups of rats dosed by oral gavage at 0, 20, 38, 75 and 1500 mg/kg bw/d.

In a first publication (Voloshina, 1985) the reproductive and developmental toxicity was investigated. On the 20th day of pregnancy, the number of corpora luttea, post-implantation loss, total fetal embryonic mortality, mass and size of embryos, the number of live and dead embryos, external and internal development anomalies, pathomorphological changes in the organs of females and fetuses were evaluated.

At 1500 mg/kg bw/d, an increase in the total embryonic and post-implantation mortality of fetuses was observed, with underdevelopment of embryos. Macroscopic examination of sections of internal organs revealed hyperemia of internal organs, pinpoint hemorrhages in the brain, liver and diaphragm, enlargement of brain ventricles and renal pelvis. The overwhelming majority of fetuses did not exhibit any alterations in the formation of bones and the osseous-articular apparatus. When observing the postnatal development of the offspring, no differences between the animals of experimental and control groups were revealed in such standard criteria as mass, eye opening and ear unfolding. However, females of the first group gave birth to 17% less pups as compared to the animals of the third and the fourth groups and the control group, which is obviously related to the prenatal mortality of embryos. Functional loads were applied (swimming, hanging on a horizontal rod) at the end of the second month from the moment of birth of the pups in order to reveal any possible hidden disorders in the body of the offspring of the first litter. It was discovered that the pups born from the females from the first group remained afloat 26% less than the animals of the remaining groups and the control group. The test involving hanging on a horizontal rod did not reveal any difference between the studied indicators in experimental and control animals. The morphological evaluation of internal organs and tissues of female white rats and their fetuses revealed the development of pathological changes. Signs of circulatory disorders and swelling of the tissue were observed in stomach and oesophagus walls, myocardium, and brain. The ovaries did not have any structural deviations, large yellow bodies predominated among the structural elements in terms of volume. The vessels were significantly expanded and hyperemic, there were moderate perivascular hemorrhages in the tissue surrounding the ovaries and in the placenta. The study of embryos revealed moderate edema of the fibrous connective tissue of the mediastinum and subcutaneous tissue, stroma of the organs and acute hyperemia of all vessels of the brain, body and internal organs. The organs and tissues of the fetuses were characterized by multiple extensive hemorrhages in the liver, mediastinum, spinal cord membranes, pleural cavity and subcutaneous tissue. Developmental lag in one of the paired organs (cerebral hemispheres, eyes, kidneys) was also observed.

At 75 mg/kg, the average weight of the embryos and the size of the placenta were lower than in the control group, and the total embryonic and post-implantation mortality of the fetuses also increased (. The macroscopic examination of the internal organs of the fetuses uncovered single cases of hemorrhages in the liver and brain and revealed dilatation of the renal pelvis. 4% of the embryos in the second group exhibited insufficient calcification of the base of skull. When studying offspring born from females of the second group, no differences between the animals of the experimental and control groups were revealed in terms of all studied indicators. The exception was the result of functional test (swimming). The floating time was 32% shorter than in the control group. The results of histological examination of organs and tissues of animals and fetuses of the second group were similar to the pathological changes revealed in rats and fetuses of the first group, while the intensity of these changes was significantly lower.

At 38 mg/kg an increase of the placental-fetal coefficient was observed. All other tests conducted during the experiment did not reveal any other changes.

At 20 mg/kg no significant changes in the absolute majority of indicators were observed.

In conclusion, Fenuron dosed at 75 and 1500 mg/kg bw/d resulted in increased prenatal mortality of the fetuses, reduced fertility, inhibited development of embryos and circulatory disorders. At 38 mg/kg bw/d, less pronounced changes were observed, and the dose of 20 mg/kg did not cause any effects in the experimental animals and was considered reproductive/developmental NOAEL.

 

In a separate publication (Talakin ,et al., 1989), the organs of the pregnant rats and embryos were subject to histological examination.

At 1500 mg/kg bw/d, the oesophagus and stomach walls, heart and brain of the rats had signs of hemodynamic abnormalities and dystrophic changes. The vessels of the brain tunics and brain substance were expanded and hyperemic; moderate perivascular edema was detected. The nerve cells of the cortex and the brainstem nuclei were in a swollen state. The mucous membrane of the stomach and oesophagus was edematous and hyperemic. The heart had cloudy swelling and uneven colouring of the myocardiocytes, sudden expansion and hyperemia of the epicardium and myocardium vessels. The cortical layer of the ovaries contained massive yellow bodies, primordial and growing follicles, and numerous atretic bodies. In the placenta, acute vascular hyperemia, single small perivascular hemorrhages, and chorion edema were observed. The layers of decidual cells penetrated deeply into the myometrium with edematous and hyperemic stroma.

At 75 mg/kg, the response of the pregnant females to the effect of the toxic agent decreased. Hemodynamic abnormalities in the stomach and oesophagus walls, myocardium, and brain were significantly weaker than at 1500 mg/kg

At 38 mg/kg an increase of the placental-fetal coefficient and changes in hemodynamics in the stomach, oesophagus walls, myocardium, and brain was observed.

At 20 mg/kg (1/400 LD50), no changes in the organs of the pregnant rats or their fetuses were detected.

In conclusion, parental toxicity was demonstrated by circulatory disorders, manifested by vascular expansion and hyperemia, edema, and sometimes small hemorrhages. In the fetuses, these changes were more significant – the edemas were diffuse, and the hemorrhages were abundant. The obtained results indicate the effect of Fenuron on the blood flow and permeability of the vascular walls, resulting in parental (maternal) and secondary fetal toxicity. The dose of 20 mg/kg bw/d was also a parental NOAEL. 

Justification for classification or non-classification

Based on these results and according to CLP (No. 1272/2008 of 16 December 2008), Fenuron does not have to be classified and has no obligatory labelling requirement for reproductive toxicity.