Cesium formate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

From January 30, 2013 to March 27, 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Read-across study

Justification for type of information:

Once taken up by the organism, cesium formate dissociates into the cesium cation (Cs) and the formate anion (HCO2 -). Toxicity is caused by the cesium cation, therefore conducting a study on cesium hydroxyde as a surrogate for cesium nitrate is justified.

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

Purity: >99.99 %; CAS No.: 7789-18-6; Batch No.: 212081S138; Aggregate State at RT: Solid; Colour: Crystals colourless; overall picture white; Odour: Odourless

Species:

rat

Strain:

Wistar

Details on species / strain selection:

Species and strain: Hsd.Brl.Han: Wist rat
Source: Toxi-Coop Zrt. Cserkesz u. 90. H-1103 Budapest, Hungary
The rat is regarded as suitable species for reproduction studies and the test guideline is designed to use the rat. The Wistar rat was selected due to a wide range of experience with this strain of rat in reproduction toxicity studies and well known fertility parameters.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
Age of animals at start: Male animals: 75 – 80 days old
Female animals: 75 – 80 days old
Body weight range at start: Male animals: 306 – 357 g; Female animals: 188 – 221 g
The weight variation in animals involved at the starting point of the study did not exceed ± 20 % of the mean group weight of each sex.
Acclimatization time: 20 days

ANIMAL HUSBENDARY
Animal health: Only healthy animals were used for the test. The breeder certified their health status.
Housing: Before mating: 2 animals of the same sex/cage; Mating: 1 male and 1 female/cage; Pregnant females were housed individually; Males after mating: 2 animals/cage
Cage type: Type II polypropylene/polycarbonate; Size: 22 x 32 x 19 cm (width x length x height)
Bedding: Lignocel® Hygienic Animal Bedding produced by J. Rettenmaier & Söhne GmbH. The bedding was suitable as nesting material. Cages and bedding material were changed twice a week.
Light: 12 hours daily, from 6.00 a.m. to 6.00 p.m.
Temperature: 22 ± 3 °C
Relative humidity: 30 - 70 %
Ventilation: 8-12 air exchanges/hour by central air-condition system.
The temperature and relative humidity was checked and recorded once daily during the study.

FOOD AND WATER SUPPLY:
Animals received ssniff® SM R/M-Z+H "Autoclavable complete feed for rats and mice – breeding and maintenance" ad libitum, and tap water from municipal supply, as for human consumption from a 500 mL bottle ad libitum. Food was changed at weekly intervals. Fresh drinking water was provided daily. The food is considered not to contain any contaminants that could reasonably be expected to affect the purpose or integrity of the study. The drinking water is periodically analyzed and is considered not to contain any contaminants that could reasonably be expected to affect the purpose or integrity of the study.

PREPARATION OF THE ANIMALS
Animals were identified by unique numbers. The individual identification was performed by a marker pen on the tail for transient identification and by ear punching for final animal numbers.

Route of administration:

oral: gavage

Vehicle:

physiological saline

Details on exposure:

The test substance was formulated in the vehicle in concentrations of 40, 10 and 2 mg/mL. Formulations were prepared in the formulation laboratory of test facility beforehand not longer than for three days before the application.

Details on mating procedure:

Males: 56 days
Females: 40 – 49 days, depending on date of mating

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analysis of formulations was performed in the analytical laboratory of test facility. Five samples were taken (5 mL, each, from different places) from each concentration (Groups 2, 3 and 4) and measured twice during the study. Similarly, five samples were taken from the control solution (5 mL, each, from different places, group 1) and analyzed.
Concentration of the test substance in the dosing formulations varied from 99 to 100 % of nominal concentrations.

The suitability of the chosen vehicle for the test substance at the intended concentrations was analytically verified up front. A sufficient recovery and stability in the chosen vehicle were verified over the range of relevant concentrations at the appropriate frequency of preparation. Recovery of the test substance 99.99 % from physiologic saline formulations was 94 % at ~1 and ~100 mg/mL concentrations. The test substance proved to be stable in physiologic saline formulations at ~1 and ~100 mg/mL concentration levels at least for 3 days at room temperature.

Duration of treatment / exposure:

Dosing of both sexes began after 20 days acclimatization and was continued up to and including the day before the necropsy.
The mating phase started after 14-days of pre-mating. Rats of this strain have already reached full sexual maturity at the age of 12 weeks. Males were dosed for 56 days (14 days pre-mating and 9 days mating plus 33 days post mating period), then they were sacrificed. Elongated treatment was reasoned by sperm analysis. Female animals were dosed for 14 days pre-mating, during mating period, through gestation and up to lactation days 3 - 7 (altogether for 40 – 49 days, depending on date of mating). The day of delivery (viz. when parturition was complete) was defined as day 0 post-partum. Non-pregnant and not delivered female animals were treated up to and including the day before necropsy (altogether for 40 days). Control animals were handled in an identical manner to the test groups
receiving only the vehicle (5 mL/kg bw/day).

Frequency of treatment:

once per day, animals not treated on the day of gross pathology

Details on study schedule:

Males:
Acclimatization period: 20 days
Pre-mating period: 14 days
Mating period: 9 days
Post-mating: 33 days
Necropsy organ weighing: day 56

Females:
Acclimatization period: 20 days
Pre-mating period: 14 days
Mating period: 9 days
Gestation period: 22-23 days
Delivery
Lactation period: 4-8 days
Necropsy: days 40 – 49

Dosing of both sexes began after 20 days acclimatization and was continued up to and including the day before the necropsy.
The mating phase started after 14-days of pre-mating. Rats of this strain have already reached full sexual maturity at the age of 12 weeks. Males were dosed for 56 days (14 days pre-mating and 9 days mating plus 33 days post mating period), then they were sacrificed. Elongated treatment was reasoned by sperm analysis. Female animals were dosed for 14 days pre-mating, during mating period, through gestation and up to lactation days 3 - 7 (altogether for 40 – 49 days, depending on date of mating). The day of delivery (viz. when parturition was complete) was defined as day 0 post-partum. Non-pregnant and not delivered female animals were treated up to and including the day before necropsy (altogether for 40 days). Control animals were handled in an identical manner to the test groups
receiving only the vehicle (5 mL/kg bw/day).

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

0 mg/mL in 5 mL volume

Dose / conc.:

10 mg/kg bw/day (nominal)

Remarks:

2 mg/mL in 5 mL volume

Dose / conc.:

50 mg/kg bw/day (nominal)

Remarks:

10 mg/mL in 5 mL volume

Dose / conc.:

200 mg/kg bw/day (nominal)

Remarks:

40 mg/mL in 5 mL volume

No. of animals per sex per dose:

12

Control animals:

yes, concurrent vehicle

Details on study design:

Mating procedure:
Mating began 2 weeks after the initiation of treatment with one female and one male of the same dose group (1:1 mating) placed in a single cage. Females remained with the same male until copulation occurred. Each morning a vaginal smear was prepared and stained with 1 % aqueous methylene blue solution. The smear was examined with a light microscope, the presence of vaginal plug or sperm in the vaginal smear was considered as evidence of copulation (day 0 of pregnancy as defined by OECD 421). Sperm positive females were caged individually. Mating pairs were clearly identified in the raw data.

Positive control:

No applicable

Parental animals: Observations and examinations:

Parental Males
− Clinical observations
− Body weight
− Body weight gain
− Food consumption
− Percentage of pairings
− Percentage of fertile pairings
− Percentage of infertile males
− Male mating index
− Male fertility index
− Necropsy findings
− Organ weights (absolute and relative to the body and brain weights)
− Sperm parameters (sperm count, sperm motility and morphology)
− Histopathology findings

Parental Females
− Clinical observations
− Body weight
− Body weight gain
− Food consumption
− Percentage of pairings
− Percentage of pregnant females
− Percentage of sperm positive, but non-pregnant females
− Percentage of non-mated females
− Female mating index
− Female fertility index
− Gestation index
− Duration of pregnancy (days)
− Number of Corpora lutea / dams
− Number of implantations / dams
− Number of dams with live pups day 0 and 4
− Pre-implantation mortality
− Post-implantation mortality
− Intra uterine mortality
− Necropsy findings
− Histopathology findings

Morbidity and mortality: twice daily (at the beginning and end of each day).

General clinical observations: once a day, after treatment at approximately. More detailed examinations were made weekly at the times of weekly weighing prior to and during the mating until necropsy. Observations were performed on the skin, fur, eyes and mucous membranes, autonomic activity (lachrymation, piloerection, pupil size, respiratory pattern, occurrence of secretions and excretions), circulatory and central nervous system, somatomotor activity and behavior pattern, changes in gait, posture and response to handling.

Examination of placental sign: All sperm positive animals were examined for vaginal bleeding (placental sign of gestation) on the 13th gestational day. If it was negative on day 13,
the examination was repeated on day 14 of gestation.

Observation of the delivery process: females were allowed to litter and rear their offspring. Delivery process was monitored whilst keeping possible interferences at a minimum.
Observations were reported individually for each animal. The duration of gestation was recorded and was calculated from day 0 of pregnancy. Dams were observed whether they made a nest from the bedding material and nurse their new-borns or not. The sucking success was observed by the presence of milk in the pups' stomach. All observations were recorded individually for each dam. Each litter was examined as soon as possible after delivery (within 24 h of parturition), to establish the number and sex of pups, stillbirths, live births, runts (pups that are significantly smaller than normal pups), and the presence of gross abnormalities. Live pups were counted, sexed, and litters weighed within 24 hours of parturition (on the day after parturition is complete), and day 4 postpartum with an accuracy of 0.1g. In addition to the observations on parent animals, any abnormal behavior of the offspring was observed. All litters were checked and recorded daily for the number of viable and dead pups. Dead pups found were subjected to necropsy by macroscopic examination. On day 0 of lactation, a lung flotation test was performed on all dead pups to separate stillborns from those that died after delivery. The ung flotation test is negative for stillborns (pups that died intrauterine) but positive for pups that died after delivery.

Oestrous cyclicity (parental animals):

Not examined

Sperm parameters (parental animals):

Sperm analysis was made from 5 control and 5 high dose males at the necropsy. A treatment related effects were seen in the sperm motility of high dose treated animals, therefore the lower dose groups were also evaluated (n=5 animals/group). One-side testes and epididymides were used for enumeration of spermatids and sperm reserves, respectively. For
this, same subset of males, sperm from the ductus deferens was collected for evaluation of sperm motility and sperm morphology.

Quantitative examination:
The total number of homogenization of testes sperm was enumerated. One side testes and epididymides were frozen at the necropsy and enumeration was performed later.
Qualitative examinations:
Sperm motility was determined from ductus deferens of the same animals as enumeration at the necropsy. For the determination of the sperm motility the mean percentage of motile sperms was determined. The number of sperm cells and immotile sperms was recorded. The number of motile cells was calculated. Two samples were prepared from each animal A morphological evaluation of ductus deferens sperms sample was performed from the same animals. Sperm was examined as fixed, wet preparations and classified as either normal or abnormal (isolated heads, misshapen heads and/or tails).

Litter observations:

− Litter weight on postnatal days 0 and 4
− Mean body weight gain per litter between postnatal days 0-4
− Number of live births per litter, and number of viable pups per litter o postnatal days 0 and 4
− Survival Index of pups on postnatal day 4
− Sex ratio % (on postnatal days 0 and 4)

Statistical evaluation was made for all above parameters.

Postmortem examinations (parental animals):

Pathology:
Gross necropsy was performed on each animal. One day after the last treatment, animals were euthanized by exsanguination after verification of
the deep narcosis by Isofluran CP® (details are presented in "Details of Other Materials"). After examination of the external appearance, the cranial, thoracic and abdominal cavities were opened and the appearance of the tissues and organs were observed, and any abnormality was recorded including details of the location, color, shape and size. Special attention was paid to the organs of the reproductive system. The number of implantation sites and of corpora lutea was recorded. The testes, epididymides and brain of all male adult animals were weighed. The uterus with cervix, vagina, testes, epididymides (total and cauda), prostate, and seminal vesicles with coagulating glands, ovaries, pituitary and all organs showing macroscopic lesions of all adult animals were preserved. Testes and epididymides were preserved in modified Davidson solution, all other organs in 4 % buffered formaldehyde solution. Dead pups and pups euthanized on postnatal day 4 were carefully examined for gross abnormalities. Four pups were fixed in isopropanol for
skeletal examinations due to the gross abnormalities observed on the skull. Then skeleton was stained with alizarin red and examined by a stereomicroscope.

Histophatology:
Detailed histological examinations were performed on the ovaries, testes and epididymides (with special emphasis on stages of spermatogenesis in
the male gonads and histopathology of interstitial testicular cell structure) of the animals in the control and high dose groups. Testes and epididymides were also examined in the lower dose groups due to the changes in sperm motility of the high dose treated animals. Detailed histological examination of the ovaries covered the follicular, luteal, and nterstitial compartments of the ovary, as well as the epithelial capsule and ovarian stroma.

Postmortem examinations (offspring):

Not examined

Statistics:

The statistical evaluation of appropriate data were performed with the statistical program package SPSS PC+4.0. The homogeneity of variance between groups was checked by Bartlett’s homogeneity of variance test. Where no significant heterogeneity was detected a one-way analysis of variance (ANOVA) was carried out. If the obtained result was significant Duncan Multiple Range test was used to access the significance of intergroup differences. Getting significant result at Bartlett’s test the Kruskal- Wallis analysis of variance was used and the inter-group comparisons were performed using Mann-Whitney U-test. Chi2 test was performed if feasible. The frequency of clinical signs, pathology and histopathology findings were calculated. Results were evaluated in comparison with values of control group (i.e. control value).

Reproductive indices:

For males: percentage of pairings; percentage of fertile pairings; percentage of infertile males; male mating index; male fertility index.
For females: percentage of pairings; percentage of pregnant females; percentage of sperm positive, but non-pregnant females; percentage of non-mated females; female mating index; female fertility index; gestation index; duration of pregnancy (days); number of corpora lutea / dams; number of implantations/dams; number of dams with live pups day 0 and 4; pre-implantation mortality; post-implantation mortality, intra uterine mortality.

Offspring viability indices:

− Number of live births per litter, and number of viable pups per litter o postnatal days 0 and 4
− Survival Index of pups on postnatal day 4

Clinical signs:

no effects observed

Description (incidence and severity):

Daily Observations:
There were no toxic signs related to the test substance effect at the daily clinical observations. The behavior and physical condition of animals were considered to be normal at each dose level (200, 50 and 10 mg/kg bw/day) during the entire observation period.
Detailed Weekly Observations:
Test substance related clinical signs were not detected at the weekly detailed observations in male or female animals at any dose level during the entire observation period (pre-mating, mating, post-mating, gestation or lactation periods).

Dermal irritation (if dermal study):

effects observed, non-treatment-related

Description (incidence and severity):

Scar was noted for one male and one female animal of 200 mg/kg bw/day group on the nose and on the neck, respectively. Scar is a common dermal finding in this strain of experimental rats and was had no toxicological meaning in this study.

Mortality:

no mortality observed

Description (incidence):

There was no mortality in 200, 50 or 10 mg/kg bw/day or control group during the course of study.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A test substance influence on the body weight development was observed in male and female animals at 200 mg/kg bw/day. More specifically, when compared to animals of the control group the body weight gain was statistically significantly reduced in male animals of 200 mg/kg bw/day group on weeks 3, 4, 5, if summarized (total body
weight gain between days 0 and 55) which resulted in a slight but statistically significantly reduced body weight during the entire postmating period. Compared to the control group, statistical significances were detected for reduced mean body weight gain of the male animals of 200 mg/kg bw/day group during the mating period, between days 27 and 34, and for the total body weight gain. The mean body weight and body weight gain of dams of 200 mg/kg bw/day were slightly but statistically significantly reduced with respect to the control on gestation day 21, between gestation days 14 and 21, as well as if summarized during the entire gestation period (between gestation days 0 and 21). The body weight development was not affected in the male or female animals treated with dose levels of 50 or 10 mg/kg bw/day with respect to the concurrent controls.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Compared to the control animals, statistically significance was observed in 200 mg/kg bw/day group for the slightly reduced mean food consumption of male animals on week 2, during the entire post-mating period and of dams between lactation days 0 and 4.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

When compared to the untreated control, a variation on the extra uterine mortality of offspring was observed in 200 mg/kg bw/day group.

Behaviour (functional findings):

not specified

Immunological findings:

not specified

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Description (incidence and severity):

Histological examination of the male and female genital organs (testes, epididymides and ovaries) did not reveal any toxic or other test substance related alterations at 200 mg/kg/bw/day dose.
In one control (1/12) and in one 200 mg/kg bw/day dose treated (1/12) animal, decreased intensity of spermatogenesis and lack of mature spermatozoa in the seminiferous tubuli of testes and in the ductuli of epididymides. In the seminiferous tubuli of affected animals decreased number of spermatids was observed, however the Sertoli-cells and spermatogonia were intact, suggesting a reversible phenomenon. Some giant-cells were detected in the tubuli of epididymides. Regarding the incidence and severity of these findings (marked degree in one control and moderate degree in one treated animal) these findings were considered as individual disorder and were not related to the test substance effect in the high dose group.
In the remaining male animals (11/12 at 200 mg/kg bw/day; 12/12 at 50 mg/kg bw/day; 12/12 at 10 mg/kg bw/day; 11/12 in the control group) the investigated organs of reproductive system (testes, epididymides) were histologically normal and characteristic on the sexually mature organism in all cases of control and treated groups.
The various spermatogenic cells (the spermatogonia, the spermatocytes, the spermatids and spermatozoa), representing different phases in the development and differentiation of the spermatozoons and the interstitial cells were the same in quantity and morphologically in the testes of investigated control and treated animals. Histologically, epididymides were normal in all cases as well. The ductuli of epididymides were crammed with nature spermatozoa.
In the female animals including non-pregnant and not delivered animals, the ovaries had a normal structure characteristic for the species, age and phase of sexual cycle. The cortex contained primary, secondary and tertiary follicles and corpora lutea, indicating the active maturation of oocytes and ovulation. The epithelial capsule and ovarian stroma were normal in all cases as well.

Histopathological findings: neoplastic:

not specified

Other effects:

not specified

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

effects observed, treatment-related

Description (incidence and severity):

Sperm examinations revealed a test substance related damage in the motility and morphology of sperm cells at 200 mg/kg bw/day. The mean percentage of immotile sperms and sperm cells with abnormal morphology (separated head and tail) was statistically significantly higher for the 200 mg/kg bw/day group (91.5 and 11.2 %, respectively) as compared to the control group (12.6 and 0.1 %, respectively). Accordingly, the percentage of motile sperm cells and sperms with normal morphology (head and tail connected) was statistically significantly lower in animals of 200 mg/kg bw/day group with respect to the control. There was no significant difference in the total sperm cell count between the control and test substance treated groups (200, 50 and 10 mg/kg bw/day).

Reproductive performance:

effects observed, non-treatment-related

Description (incidence and severity):

There were no test substance related differences between the control and test substance treated male animals in the examined parameters of reproductive performance. Statistical significances were noted for the higher percentage of fertile males and pregnant females, consequently for higher fertility indices (male and female) and for the less percentage of infertile males and non-pregnant females in all test substance treated groups (200, 50 and 10 mg/kg bw/day). The gestation index was slightly less in dams of 200 mg/kg bw/day. These slight differences with respect to control were indicative of biological variation and had no toxicological relevance.

Key result

Dose descriptor:

NOAEL

Effect level:

ca. 50 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

reproductive performance

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

The number and percentage of offspring with clinical signs (not suckled, cold) and number and percentage of missing (cannibalized) offspring were significantly higher in the 200 mg/kg bw/day group comparing to their control. A hole on the skullcap was observed in one male pup of 200 mg/kg bw/day group, which therefore was euthanized on postnatal day 0. This individual finding was considered as incidental. Test substance related clinical signs did not appear in the pups of 50 or 10 mg/kg bw/day groups. Abnormal mandible as individual variation was noted for one male pup in group of 10 mg/kg bw/day.

Dermal irritation (if dermal study):

not specified

Mortality / viability:

mortality observed, treatment-related

Description (incidence and severity):

In the 200 mg/kg bw/day group the litter mean and percentage of dead (missing, found dead and early euthanized) offspring were statistically significantly higher than in the control group between postnatal days 0 and 4. The mean number of the live-borns (male + female, female) and viable offspring on the postnatal days 0 (male + female, female) and 4 (male + female, male and female) were statistically significantly lower than in the control group in group of 200 mg/kg bw/day. However, these findings only slightly differ with respect to the untreated control but a causal link to the treatment with the test item cannot be excluded. The number and percentage of liveborns and viable offspring, extra uterine mortality between postnatal days 0 and 4 were similar in the control, 50 and 10 mg/kg bw/day groups.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Variations on the body weight of offspring in 200 mg/kg bw/day group were detected. More specifically, compared to the control group, the mean litter weight and the mean litter weight gain were statistically significantly less at 200 mg/kg bw/day group on postnatal days 0 and 4, as well as between postnatal days 0 and 4, respectively. Although different to the untreated control, these values remained within the ranges of the historical control data. Similarly, the mean offspring’s weight and weight gain remained below the control value in 200 mg/kg bw/day group on postnatal days 0 and 4, as well as between postnatal days 0 and 4. However, these findings only slightly differ with respect to the untreated control but a causal link to the treatment with the test substance cannot be excluded. Statistical significances were also detected at the less mean body weight of pup in 50 mg/kg bw/day group at the birth and on postnatal day 4. However the differences were with low degree in the middle dose group with respect to the control therefore was not considered to be toxicologically relevant. The mean litter weight and mean pup weight were similar in the control and 10 mg/kg bw/day dose treated groups, no test substance related changes were found.

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not examined

Clinical biochemistry findings:

not specified

Urinalysis findings:

not examined

Sexual maturation:

not specified

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

The external examinations revealed abnormal findings in individual pups of 200 mg/kg bw/day: one with edemic and deformed lips, one stillborn pup with morphological alterations on the head (cranium and splancnocranium) and one euthanized pup with a hole on the skullcap. As these isolated findings were observed only in individual pups from different litters and were not associated with other morphological alterations, a test substance relationship is considered as unlikely. Thus, these scattered occurrences are finally considered as incidental. In one pup of 10 mg/kg bw group, the mandible was abnormal. Test substance related macroscopic alterations were not found in viscera of
offspring subjected to gross pathological examination.

Histopathological findings:

not examined

Other effects:

no effects observed

Description (incidence and severity):

There were no significant differences between control and test substance treated groups in the ratio or in the litter means of genders on postnatal days 0 or 4.

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

ca. 50 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

mortality

body weight and weight gain

Remarks on result:

other:

Remarks:

higher incidence of clinical signs, higher extra uterine mortality, depressed body weight development (for litter and pup weights). These findings only slightly differ with respect to the untreated control but a causal link to the treatment with the test substance cannot be excluded (equivalent to 50.3 mg cesium formate monohydrate/kg bw/day).

Key result

Reproductive effects observed:

yes

Lowest effective dose / conc.:

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

Treatment related:

yes

Relation to other toxic effects:

reproductive effects occurring together with other toxic effects, but not as a secondary non-specific consequence of other toxic effects

Dose response relationship:

yes

Relevant for humans:

not specified

Conclusions:

Under the study conditions, the no observed adverse effect levels (NOAEL) were determined as follows: NOAEL for male rats: 50 mg/kg bw/day, NOAEL for female rats: 50 mg/kg bw/day, NOAEL for reproductive performance of the male rats: 50 mg/kg bw/day NOAEL for reproductive performance of the female rats: 50 mg/kg bw/day, NOAEL for F1 Offspring: 50 mg/kg bw/day.

Executive summary:

A study was conducted to determine the reproductive and developmental toxicity of cesium nitrate when administered to rats for a minimum of 28 days according to OECD Guideline 421 (reproduction/developmental toxicity screening test) and EPA OPPTS 870.3550, in compliance with GLP. The test substance, formulated inphysiologic saline, was administered daily by oral gavage to Hsd.Brl.Han:Wist rats. One control group of vehicle and three treated groups (10, 50 and 200 mg/kg bw/day) were tested, each consisting of 12 males and 12 females. All animals of the parent (P) generation received test substance or vehicle prior to mating (14 days) and throughout mating. Test substance or vehicle was administered to male animals post mating (altogether for 56 days) up to the day before necropsy. For dams, the test substance was administered through the gestation period and up to postpartal days 3 - 7 (altogether for 40 – 49 days), i.e. up to the day before the necropsy. For the parental generation, observations included mortality, clinical signs, body weight, food consumption and the following reproduction parameters: gonadal function, mating behavior, conception, pregnancy and parturition. The dams were allowed to litter and rear their young up to termination on Day 4 postpartum. All parental animals were subjected to gross pathology. Histopathology examination was performed on the testes, epididymides in all male animals and on ovaries in female animals of the control and high dose groups. The offspring were evaluated from conception to Day 4 postpartum. Pups were weighed and observed for possible abnormalities. Four pups were fixed in isopropanol and stained with Alizarin-Red for skeletal examinations due to externally observed abnormalities. Treatment-related clinical and reproduction effects were found at 200 mg/kg bw/day: reduced body weight, body weight gain and reduced food consumption (male and female), changes in delivery data of dams (postimplantation loss, live-borns, viable pups), damage in sperm motility and morphology, slightly reduced weights of testes, epididymides. At 50 and 10 mg/kg bw/day, there were no test substance-related effects in the parental male or female animals. At 200 mg/kg bw/day, variations in offspring development were detected: higher incidence of clinical signs, higher extra uterine mortality, depressed body weight development (for litter and pup weights). These findings only slightly differed with respect to the untreated control but a causal link to the treatment with the test substance could be excluded. Also, morphological alterations of the skull in individual pups of different litters were observed. These scattered occurrences, only observed in individual pups from different litters, were considered as incidental. Under the study conditions, the NOAELs were determined as follows: NOAEL for male and female rats: 50 mg/kg bw/day, NOAEL for reproductive performance of the male and female rats: 50 mg/kg bw/day, NOAEL for F1 offspring: 50 mg/kg bw/day (equivalent to 50.3 mg cesium formate monohydrate/kg bw/day) (Pascis Szakonyine, 2013).

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

15 mg/kg bw/day

Study duration:

subacute

Species:

rat

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 study was conducted to determine the reproductive and developmental toxicity of cesium nitrate when administered to rats for a minimum of 28 days according to OECD Guideline 421 (reproduction/developmental toxicity screening test) and EPA OPPTS 870.3550, in compliance with GLP.The test substance, formulated inphysiologic saline,was administered daily by oral gavage toHsd.Brl.Han:Wist rats. One control group of vehicle and three treated groups (10, 50 and 200 mg/kg bw/day) were tested, each consisting of 12 males and 12 females. All animals of the parent (P) generation received test substance or vehicle prior to mating (14 days) and throughout mating. Test substance or vehicle was administered to male animals post mating (altogether for 56 days) up to the day before necropsy. For dams, the test substance was administered through the gestation period and up to postpartal days 3 - 7 (altogether for 40 – 49 days), i.e. up to the day before the necropsy. For the parental generation, observations included mortality, clinical signs, body weight, food consumption and the following reproduction parameters: gonadal function, mating behavior, conception, pregnancy and parturition. The dams were allowed to litter and rear their young up to termination on Day 4 postpartum. All parental animals were subjected to gross pathology. Histopathology examination was performed on the testes, epididymides in all male animals and on ovaries in female animals of the control and high dose groups. The offspring were evaluated from conception to Day 4 postpartum. Pups were weighed and observed for possible abnormalities. Four pups were fixed in isopropanol and stained with Alizarin-Red for skeletal examinations due to externally observed abnormalities. Treatment-related clinical and reproduction effects were found at 200 mg/kg bw/day: reduced body weight, body weight gain and reduced food consumption (male and female), changes in delivery data of dams (postimplantation loss, live-borns, viable pups), damage in sperm motility and morphology, slightly reduced weights of testes, epididymides. At 50 and 10 mg/kg bw/day, there were no test substance-related effects in the parental male or female animals. At 200 mg/kg bw/day, variations in offspring development were detected: higher incidence of clinical signs, higher extra uterine mortality, depressed body weight development (for litter and pup weights). These findings only slightly differed with respect to the untreated control but a causal link to the treatment with the test substance could be excluded. Also, morphological alterations of the skull in individual pups of different litters were observed. These scattered occurrences, only observed in individual pups from different litters, were considered as incidental. Under the study conditions, the NOAELs were determined as follows: NOAEL for male and female rats: 50 mg/kg bw/day, NOAEL for reproductive performance of the male and female rats: 50 mg/kg bw/day, NOAEL for F1 offspring: 50 mg/kg bw/day (equivalent to 50.3 mg cesium formate monohydrate/kg bw/day) (Pascis Szakonyine, 2013).

As mentioned in the section ‘Repeated dose toxicity’, a study was conducted to assess the systemic toxicity of cesium (Cs) in a 13 week oral gavage study in Han Wistar rats followed by a recovery period of up to 16 weeks, according to OECD 408, in compliance with GLP. This study was designed to investigate the relationship between the toxicity produced by Cs (e.g. uremia, hypokalemia, alkalosis) and male reproductive effects (e.g. decrease in sperm motility, decrease in spermatogenesis). The study showed that oral administration of cesium chloride (CsCl) to Han Wistar rats at doses of 13, 38, 127 or 253 mg/kg bw/day resulted in pathological changes in the mandibular and sublingual salivary glands, heart, stomach, spleen, adrenals, mammary glands, skin and subcutis, epididymides and testes of animals treated at 253 mg/kg bw/day for 59 days or 127 mg/kg bw/day for 13 weeks. Additional changes were seen in the kidneys, skeletal muscles, extremities, ovaries and uterus of animals treated at 253 mg/kg bw/day. At 38 mg/kg bw/day, treatment-related changes were seen in the adrenals and testes. In addition, changes in the blood and urine indicative of an effect on kidney function were apparent at doses of 38 mg/kg bw/day and above; in particular, there was a clear increase in plasma urea and decrease in plasma potassium which was dose-related and marked at the 127 and 253 mg/kg bw/day dose levels. There was a dose-dependent detrimental effect on maturation of the sperm with most sperm breaking down within the epididymis. Treatment at 127 or 253 mg/kg bw/day resulted in most males showing no motile or normal sperm and significant reductions in sperm numbers. There was also a significant reduction in total sperm number in the cauda epididymis at 38 mg/kg bw/day and a slight effect on sperm morphology. The dose of 253 mg/kg bw/day clearly exceeded the maximum tolerated dose and treatment at this dose level was stopped in Week 9. Recovery from all treatment-related changes was demonstrated, though one male receiving 127 mg/kg bw/day, still showed changes in the testes with associated low sperm numbers, all of which were immotile and abnormal after 16 weeks of recovery. No change on sperm numbers, morphology or motility or any pathological changes were seen at 13 mg/kg /day, nor were there any indications of an effect on the kidney. Consequently, based on these findings, the NOAEL was considered to be 13 mg/kg bw/day (equivalent to 15 mg cesium formate monohydrate/kg bw/day) (Webley, 2016).

Effects on developmental toxicity

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

From July 23, 2013 to January 09, 2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Read across study

Justification for type of information:

Once taken up by the organism, cesium formate dissociates into the cesium cation (Cs) and the formate anion (HCO2 -). Toxicity is caused by the cesium cation, therefore conducting a study on cesium hydroxyde as a surrogate for cesium formate is justified.

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

No significant deviations to study plan which affected the outcome of the study.

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

other: Hsd.Brl.Han: of Wistar origin

Details on test animals or test system and environmental conditions:

- Source: Charles River (Europe) Laboratories Inc. Toxi-Coop Zrt. 1103 Budapest, Cserkesz u. 90. Hungary
- Age: Females: Young adult and nulliparous females, 11-12 weeks of age at start of the mating period
Males: experienced males used in the developmental DRF study (Study no.: 559.410.3533), 23-24 weeks of age at start of the mating period
- Bodyweight: The group averages of the body weight were as similar as possible on the first day of gestation
- Housing:
Before mating: 1-3 females /cage 1-2 males/cage
Mating: 1 male and 1-3 females / cage
During gestation: 2-3 sperm positive females /cage, if not possible 1 sperm positive female per cage
- Cage type:
Type II polypropylene/polycarbonate
- Bedding:
Lignocel Hygienic Animal Bedding produced by J. Rettenmaier & Söhne GmbH+Co.KG (D-73494 Rosenberg, Holzmühle 1, Germany). Details of bedding quality were reported (Appendix XXIII).
- Light:
12 hours daily, from 6.00 a.m. to 6.00 p.m.
- Temperature:
21-22 °C
- Relative humidity:
40 - 54 %
- Ventilation:
8-12 air exchanges/hour by central air-condition system.
The temperature and relative humidity were checked and recorded once daily during the study. Any deviations were documented.

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:

The test item was formulated in the vehicle (distilled water) in concentrations of 1, 4, and 15 mg/mL.
Formulations were prepared daily to weekly. Due to the corrosive properties of the test item, the pH value of the formulations was adjusted to pH 7-9 with HCl prior to gavage administration. The suitability of the chosen vehicle for the test item at the intended concentrations was analytically verified up front. A sufficient stability and homogeneity in the chosen vehicle were verified over the range of relevant concentrations at the appropriate frequency of preparation.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analytical control (concentration, homogeneity) of dosing solutions was performed twice during the treatment period. The Cesiumhydroxidmonohydrat 99.95 concentrations in the samples were found to be 94 – 95 % in comparison to the nominal values.

Details on mating procedure:

The females were paired to males in the mornings for two to four hours (one male: one to three females) until the number of sperm positive females / group achieved at least twenty four. Vaginal smears were prepared from each female, stained with 1 % aqueous methylene blue solution and examined for presence of sperm and for estrus cycle stage.
The day of mating was regarded as day 0 of pregnancy (vaginal plug and/or sperm in the vaginal smear). Sperm positive females were separated and caged in groups of 2 to 3 animals (if not possible one female per cage). Caging of the females individually was avoided except in case of three dams.

Duration of treatment / exposure:

The sperm positive females were treated from gestational day 5 to 19.

Frequency of treatment:

The test item was administered in a single dose by oral gavage (stomach tube) on a 7 days/week basis every day at similar time.

Dose / conc.:

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

Remarks:

Controls

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose:

25 females for the controls, 27 females for the treated groups.

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on the results of a 28 day oral toxicity study

Maternal examinations:

CLINICAL EXAMINATIONS
General clinical observations of the females were made once a day from day 0 up to day 19 which were performed after treatment at approximately the same time during the treatment period, considering the peak period of anticipated effects after dosing. Individual observation included the check of behavior and general condition.
Observations for signs of morbidity and mortality were made twice daily, at the beginning of the working period and in the afternoon.

BODYWEIGHT
The body weight of the male animals was not measured.
The body weight of all female rats was measured at least once in the pre-mating period, but was not statistically evaluated. Body weight of sperm positive females was measured on gestation days 0, 3, 5, 8, 11, 14, 17 and 20 (accuracy of 1 g).
The corrected body weight was calculated for day 20 of pregnancy (body weight on day 20 minus the weight of the gravid uterus).

FOOD CONSUMPTION
Food consumption was determined between gestation days 0 to 3, 3 to 5, 5 to 8, 8 to 11, 11 to 14, 14 to 17 and 17 to 20 by weighing the diet at the start of each measurement period and by re-weighing the non-consumed diet at the end of the respective period (accuracy: 1 g).

PLACENTAL SIGNS
All sperm positive animals were examined for vaginal bleeding (placental sign of gestation) on the 13th gestational day. If negative on day 13, the examination was repeated on day 14 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 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]
- Head examinations: Yes: [half per litter]

Statistics:

The statistical evaluation of data was performed with the program package SPSS PC+4.0.
The homogeneity of variance between groups was checked by Bartlett’s homogeneity of variance test.
Where no significant heterogeneity was detected a one-way analysis of variance (ANOVA) was carried out. If the obtained result was significant Duncan’s Multiple Range test was used to access the significance of inter-group differences. If a significance was the result of the Bartlett’s test, the Kruskal-Wallis analysis of variance was used and the inter-group comparisons were performed using Mann-Whitney U-test.

Historical control data:

Yes

Clinical signs:

no effects observed

Description (incidence and severity):

There were no clinical signs or treatment related necropsy findings recorded for the dams.

Mortality:

no mortality observed

Description (incidence):

None of the pregnant females died in the course of the study before scheduled necropsy.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A statistically significant reduction in the food consumption was to see in the mid and high dose group (40 and 150 mg/kg bw/day) from gestational day 14 up to necropsy if compared to the control. This reduction in the food consumption was observed in association with a statistically significantly lower body weight gain in the high dose group noted during the last three days of the study and during the whole in-life phase. Corrected body weight gain in the mid and high dose groups was also statistically significantly reduced. These findings were attributed to an effect of the test substance.
The slightly reduced food consumption of the dams which was statistically significant in the mid dose group (40 mg/kg bw/day) between days 11 to 14 (without a dose response) and the slightly lower food consumption of the dams in the low dose group (10 mg/kg bw/day) associated with no changes in the body weight parameters and were considered to be incidental.
There were no significant differences in the body weight and body weight gain of the dams in the low and mid dose groups (0 and 40 mg/kg bw/day).

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

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:

not examined

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

not examined

Number of abortions:

not examined

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

There was no effect related to the administration of the test substance in the preimplantation loss, intrauterine mortality of the conceptuses, the number of implantations, viable fetuses and their sex distribution.

Total litter losses by resorption:

no effects observed

Early or late resorptions:

no effects observed

Dead fetuses:

no effects observed

Changes in pregnancy duration:

not examined

Description (incidence and severity):

Migrated Data from removed field(s)
Field "Effects on pregnancy duration" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsMaternalAnimals.MaternalDevelopmentalToxicity.EffectsOnPregnancyDuration): not examined

Changes in number of pregnant:

not examined

Other effects:

not examined

Key result

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Basis for effect level:

body weight and weight gain

Remarks on result:

other:

Remarks:

equivalent to 12 mg cesium formate monohydrate/kg bw/day

Key result

Abnormalities:

no effects observed

Fetal body weight changes:

no effects observed

Description (incidence and severity):

Migrated Data from removed field(s)
Field "Fetal/pup body weight changes" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsFetuses.FetalPupBodyWeightChanges): no effects observed

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

not examined

Changes in postnatal survival:

not examined

External malformations:

no effects observed

Skeletal malformations:

no effects observed

Visceral malformations:

no effects observed

Other effects:

no effects observed

Key result

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no effects

Remarks on result:

other:

Remarks:

equivalent to 175 mg cesium formate monohydrate/kg bw/day

Key result

Abnormalities:

no effects observed

Key result

Developmental effects observed:

no

Conclusions:

Under the study conditions, the NOAEL for maternal toxicity was determined to be 10 mg/kg bw/day (equivalent to 12 mg cesium formate monohydrate/kg bw/day) and the NOAEL for developmental toxicity was 150 mg/kg bw/day (equivalent to 175 mg cesium formate monohydrate/kg bw/day).

Executive summary:

A study was conducted to determine the prenatal developmental toxicity of the read across substance cesium hydroxide monohydrate 99.95 according to OECD Guideline 414, in compliance with GLP. Groups of 27 sperm-positive female Hsd. Brl. Han: WISTAR rats were treated with the test substance by oral administration daily at 10, 40 and 150 mg/kg bw/day from Day 5 up to and including Day 19 post coitum. A control group of 25 sperm positive females was included and the animals were given the vehicle distilled water. The treatment volume was 10 mL/kg bw. During the study, mortality was checked for and clinical observations were performed. Body weight and food consumption of the dams were also recorded. The day when sperm was detected in the vaginal smear was regarded as Day 0 of gestation. A Caesarean section and gross pathology were performed on Gestational Day 20. The number of implantations, early and late resorptions, live and dead fetuses in each uterine horn and the number of corpora lutea were recorded. Each fetus was weighed and examined for sex and gross external abnormalities. The placentas were weighed and examined externally. About half of each litter was preserved for visceral examination and the other half of the litters were preserved for skeletal evaluation. At visceral examination the bodies were micro dissected by means of a dissecting microscope. The heads were examined by Wilson's free-hand razor blade method. After cartilage-bone staining the skeletons were examined by means of a dissecting microscope. All abnormalities found during the fetal examinations were recorded.None of the pregnant females died in the course of the study before scheduled necropsy. There were no clinical signs or treatment related necropsy findings recorded for the dams. A statistically significant reduction in the food consumption was seen at 40 and 150 mg/kg bw/day from Gestational Day 14 up to necropsy compared to the control. This reduction in the food consumption was observed in association with a statistically significantly lower body weight gain in the high dose group noted during the last three days of the study and during the whole in-life phase. Corrected body weight gain in the mid and high dose groups was also statistically significantly reduced. These findings were attributed to an effect of the test substance. The slightly reduced food consumption of the dams which was statistically significant at 40 mg/kg bw/day between Days 11 to 14 (without a dose response) and the slightly lower food consumption of the dams at 10 mg/kg bw/day associated with no changes in the body weight parameters and were considered to be incidental. There were no significant differences in the body weight and body weight gain of the dams at 0 and 40 mg/kg bw/day.There was no effect related to the administration of the test substance in the preimplantation loss, intrauterine mortality of the conceptuses, the number of implantations, viable fetuses and their sex distribution. The mean fetal weight, placental and relative placental weight were similar across the control and test substance treated groups. The distribution of external, visceral and skeletal variations was homogenous among the experimental groups. There were no malformations found during external and visceral evaluation of the fetuses and there were no significant differences in the skeletal malformations if compared to the control. Under the study conditions, the NOAEL for maternal toxicity was determined to be 10 mg/kg bw/day (equivalent to 12 mg cesium formate monohydrate/kg bw/day) and the NOAEL for developmental toxicity was 150 mg/kg bw/day (equivalent to 175 mg cesium formate monohydrate/kg bw/day) (Toxi-COOP, 2013).

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

175 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

Good quality database

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

A study was conducted to determine the prenatal developmental toxicity of the read across substance cesium hydroxide monohydrate 99.95 according to OECD Guideline 414, in compliance with GLP. Groups of 27 sperm-positive female Hsd. Brl. Han: WISTAR rats were treated with the test substance by oral administration daily at 10, 40 and 150 mg/kg bw/day from Day 5 up to and including Day 19 post coitum. A control group of 25 sperm positive females was included and the animals were given the vehicle distilled water. The treatment volume was 10 mL/kg bw. During the study, mortality was checked for and clinical observations were performed. Body weight and food consumption of the dams were also recorded. The day when sperm was detected in the vaginal smear was regarded as Day 0 of gestation. A caesarean section and gross pathology were performed on Gestational Day 20. The number of implantations, early and late resorptions, live and dead fetuses in each uterine horn and the number of corpora lutea were recorded. Each fetus was weighed and examined for sex and gross external abnormalities. The placentas were weighed and examined externally. About half of each litter was preserved for visceral examination and the other half of the litters were preserved for skeletal evaluation. At visceral examination the bodies were micro dissected by means of a dissecting microscope. The heads were examined by Wilson's free-hand razor blade method.After cartilage-bone staining the skeletons were examined by means of a dissecting microscope. All abnormalities found during the fetal examinations were recorded.None of the pregnant females died in the course of the study before scheduled necropsy. There were no clinical signs or treatment related necropsy findings recorded for the dams. A statistically significant reduction in the food consumption was seen at 40 and 150 mg/kg bw/day from Gestational Day 14 up to necropsy compared to the control. This reduction in the food consumption was observed in association with a statistically significantly lower body weight gain in the high dose group noted during the last three days of the study and during the whole in-life phase. Corrected body weight gain in the mid and high dose groups was also statistically significantly reduced. These findings were attributed to an effect of the test substance. The slightly reduced food consumption of the dams which was statistically significant at 40 mg/kg bw/day between Days 11 to 14 (without a dose response) and the slightly lower food consumption of the dams at 10 mg/kg bw/day associated with no changes in the body weight parameters and were considered to be incidental. There were no significant differences in the body weight and body weight gain of the dams at 0 and 40 mg/kg bw/day.There was no effect related to the administration of the test substance in the preimplantation loss, intrauterine mortality of the conceptuses, the number of implantations, viable fetuses and their sex distribution. The mean fetal weight, placental and relative placental weight were similar across the control and test substance treated groups. The distribution of external, visceral and skeletal variations was homogenous among the experimental groups. There were no malformations found during external and visceral evaluation of the fetuses and there were no significant differences in the skeletal malformations if compared to the control. Under the study conditions, the NOAEL for maternal toxicity was determined to be 10 mg/kg bw/day (equivalent to 12 mg cesium formate monohydrate/kg bw/day) and the NOAEL for developmental toxicity was 150 mg/kg bw/day (equivalent to 175 mg cesium formate monohydrate/kg bw/day) (Toxi-COOP, 2013).

Justification for classification or non-classification

In a 28 day study with cesium formate, effects in male reproductive organs (testes and epidydimis) were seen at the highest tested dose. However, it appeared that the reprotoxic effects may have been the result of the overt toxicity observed at this dose. Studies with exposures exceeding 28 days showed additional effects on epididymal and testes weights and sperm maturation in particular in the epididymis. Sperm motility and morphology were the most sensitive endpoints for effects on the reproductive organs, but were always accompanied by indications of functional impairment of the kidney as evidenced by increased BUN levels, and decreases in potassium serum levels. Even in a recent 90 day study with narrower dose spacing (see repeated dose toxicity section), these effects could not be separated. The study indicated that reproductive toxicity was likely to be secondary to other effects, however a direct effect could not be completely ruled out.

It is important to note that the toxicity present at the dose levels that produce sperm effects is severe in nature and that the lowest systemic LOAEL for sperm toxicity in the rat (e.g. slight increase in the incidence of abnormal sperm) is higher than the lowest systemic LOAEL for cardiovascular toxicity (QT-prolongation) in man. When humans are exposed to cesium salts, cardiovascular effects would be observed before any effects on the male reproductive system would become evident. Human data would justify classification for effects on the heart, and not for reproductive toxicity.

Given the uncertainly on the mode of action of cesium and the limited relevance of the reproductive effects for man, a classification for cesium formate as Reproductive Toxicity Category 2 – Suspected human reproductive toxicant according toexposure according to CLP (EC 1272/2008) criteriais proposed.

A complete justification for this classification is provided in Section 13 of the IUCLID.