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Administrative data

Key value for chemical safety assessment

Effects on fertility

Description of key information

Effects on fertility: via oral route
No data are available on the toxicity of yttrium zirconium oxide to reproduction. One study exists wit the read across substance zirconium acetate. Rossiello (2013) performed a combined repeated dose toxicity study with reproduction/developmental toxicity screening test via oral route in rats according to OECD guideline 422 (GLP). A NOAEL of >=1000 mg/kg bw/day was obtained (based on anhydrous zirconium acetate).

Link to relevant study records

Referenceopen allclose all

Endpoint:
screening for reproductive / developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2012-12-06 to 2013-02-07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Italia S.p.A., Calco (Lecco), Italy
- Age at study initiation: 6 to 7 weeks
- Weight at study initiation: 204.5 to 212.8 g (males); 164.8 to 180.2 g (females)
- Fasting period before study: none
- Housing: From arrival to pairing, animals were housed up to 5 of one sex to a cage, in polisulphone solid bottomed cages measuring 59.5 x 38 x 20 cm. Nesting material was provided inside suitable bedding bags and changed at least twice a week. During mating, animals were housed one male to one female in clear polycarbonate cages measuring approximately 43 x 27 x 18 cm with a stainless steel mesh lid and floor. Each cage tray held absorbent material which was inspected and changed daily. After mating, the males were re-caged as they were before mating while females were transferred to individual solid bottomed cages for the gestation period, birth and lactation.
- Diet: ad libitum, except prior to drawing of blood for clinical chemistry examinations
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2
- Humidity (%): 55 +/- 15%
- Air changes (per hour): 15 to 20
- Photoperiod (hours dark / hours light): 12/12
Route of administration:
oral: gavage
Vehicle:
other: purified water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS
The required amount of zirconium acetate solution (containing 40.7% of zirconium acetate anhydrous) was dissolved in the vehicle (purified water) to obtain final concentrations of 10, 30 and 100 mg/mL. The formulations were prepared daily or up to 7 days before dosing according to stability data. The concentrations were calculated and expressed in terms of zirconium acetate content (40.7%).

VEHICLE
- Concentration in vehicle: 10, 30, 100 mg/L (expressed as active compound content)
- Amount of vehicle (if gavage): 10 mL/kg body weight (for males, dose volumes were adjusted once per week for each animal according to the last recorded body weight; for females, dose volumes were calculated according to individual body weight on days 0, 7, 14 and 20 post coitum and on day 1 post partum, thereafter individual dose volumes remained constant)
- Purity: not requiered

Details on mating procedure:
- M/F ratio per cage: 1/1
- Length of cohabitation: 2 weeks
- Proof of pregnancy: vaginal plug or sperm in vaginal smear referred to as day 0 post coitum
- After 14 days of unsuccessful pairing the paired animals were separated.
- After successful mating each pregnant female was transferred to an individual solid bottomed cages for the gestation period, birth and lactation.
- Any other deviations from standard protocol: none
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Prior to commencement of treatment, analysis was performed to confirm that the proposed formulation procedure was acceptable (check of concentration) Samples of dosing formulations prepared on Weeks 1 and 5 were analysed to verify the concentrations. Samples of the formulations were collected and sent at ambient temperature to the analytical laboratory. Chemical analyses were carried out according to an Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) method.
Duration of treatment / exposure:
- Males were treated two weeks prior to pairing, throughout pairing and thereafter through the day before scheduled sacrifice (32 days of dosing).
- Females were treated two weeks prior to pairing, throughout pairing until day 3 post partum or the day before scheduled sacrifice (up to 50 days of dosing).
Frequency of treatment:
Once daily
Details on study schedule:
- Age at mating of the mated animals in the study: 10 to 11 weeks
Dose / conc.:
100 mg/kg bw/day (actual dose received)
Remarks:
zirconium acetate anhydrous
Dose / conc.:
300 mg/kg bw/day (actual dose received)
Remarks:
zirconium acetate anhydrous
Dose / conc.:
1 000 mg/kg bw/day (actual dose received)
Remarks:
zirconium acetate anhydrous
Dose / conc.:
53 mg/kg bw/day (actual dose received)
Remarks:
based on zirconium
Dose / conc.:
159 mg/kg bw/day (actual dose received)
Remarks:
based on zirconium
Dose / conc.:
530 mg/kg bw/day (actual dose received)
Remarks:
based on zirconium
No. of animals per sex per dose:
10
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: dose levels were selected in consultation with the sponsor based on information from a non-GLP 2 week preliminary toxicity study (RTC Study no. 94150EXT).
- Rationale for animal assignment: rats were allocated to groups by computerised stratified randomisation to give approximately equal initial group mean body weights.
- Rationale for selecting satellite groups: not applicable (satellite group not included)
- Post-exposure recovery period in satellite groups: not applicable (satellite group not included)
Positive control:
None
Parental animals: Observations and examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Animals were checked each morning and afternoon for mortality.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Once before commencement of treatment and at least once daily during the study, each animal was observed and any clinical sign was recorded. Observations were performed at the same time interval each day, the interval was selected taking into consideration the presence of post-dose reactions.

BODY WEIGHT: Yes
- Time schedule for examinations: Males were weighed weekly from allocation to termination. Females were weighed weekly from allocation to positive identification of mating and on Days 0, 7, 14 and 20 post coitum. Dams were also weighed on Days 1 and 4 post partum.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: weekly during the pre-mating period starting from allocation. Individual food consumption for the females was measured on Days 7, 14 and 20 post coitum starting from Day 0 post coitum and on Day 4 post partum starting from Day 1 post partum.
- Parameters checked: the weight of food consumed by each cage of males and females.

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: as part of the sarificial procedure
- Anaesthetic used for blood collection: yes (isofluorane)
- Animals fasted: yes
- How many animals: 5 per sex
- Parameters checked: haematocrit; haemoglobin; red blood cell count; reticulocyte count; mean red blood cell volume; mean corpuscular haemoglobin; mean corpuscular haemoglobin concentration; white blood cell count; differential leucocyte count (neutrophils, lymphocytes, eosinophils, basophils, monocytes, large unstained cells); platelets

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: as part of the sarificial procedure
- Anaesthetic used for blood collection: yes (isofluorane)
- Animals fasted: yes
- How many animals: 5 per sex (females with viable litters if possible)
- Parameters checked: alkaline phosphatase; alanine aminotransferase; aspartate aminotransferase; gamma-glutamyltransferase; urea; creatinine; glucose; triglycerides; bile acids; phosphorus; total bilirubin; total cholesterol; total protein; albumin; globulin; A/G Ratio; sodium; potassium; calcium; chloride.

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: for males 5 days before necropsy and for females on Day 3 post partum.
- Dose groups that were examined: from each group, 5 males and 5 females were randomly selected.
- Battery of functions tested: grip strength; sensory reactivity to stimuli; motor activity assessment

FUNCTIONAL OBSERVATION BATTERY TESTS: Yes
- Time schedule for examinations: once before commencement of treatment and at least once a week thereafter, each animal was given a detailed clinical examination.
- Battery of functions tested: removal (from cage); handling reactivity; lachrymation; palpebral closure; salivation; piloerection; rearing; spasms; myoclonia; mobility impairment; arousal (animal activity); vocalisation; stereotypies; unusual respiratory pattern; bizarre behaviour; urination; defecation; tremors; gait.
Oestrous cyclicity (parental animals):
- Vaginal smears were taken daily in the morning starting two weeks before pairing until a positive identification of copulation was made. The vaginal smear data were examined to determine any anomalies of the oestrous cycle.
Sperm parameters (parental animals):
Parameters examined in all P males:
- testis weight, epididymis weight
- spermatogenic cycle: A detailed qualitative examination of the testes was performed in control and high dose groups. The evaluation, taking into account the tubular stages of the spermatogenic cycle, was conducted in order to identify treatment-related effects, such as missing germ cell layers or types, retained spermatids, multinucleated or apoptotic germ cells and sloughing of spermatogenic cells into the lumen. Seminiferous tubules were evaluated with respect to their stage in the spermatogenic cycle and to the integrity of the various cell types within the different stages.
Litter observations:
STANDARDISATION OF LITTERS: No

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring: number and sex of pups; stillbirths; live births; postnatal mortality; presence of gross anomalies; weight gain; and physical or behavioural abnormalities.

GROSS EXAMINATION OF DEAD PUPS:
yes, for pups surviving to day 4 post partum and for pups killed or dying during the lactation period
Postmortem examinations (parental animals):
SACRIFICE
- All parental animals were killed by exsanguination under isofluorane anaesthesia.
- Male animals: All surviving males were sacrificed after mating of all females was complete (after 32 days of treatment period).
- Femalel animals: Females with live pups were killed on Day 4 post partum while females which did not give birth 25 days after positive identification of mating were killed shortly (Day 27 post coitum).

TISSUE PRESERVATION: Yes
- Procedure: Samples of tissues were fixed and preserved in 10% neutral buffered formalin (except eyes, testes and epididymides which were fixed in modified Davidson's fluid and preserved in 70% ethyl alcohol).
- Organs / tissues preserved: all abnormalities; adrenal glands; bone marrow (from sternum); brain; caecum; colon; duodenum; heart; ileum; jejunum (including Peyer’s patches); kidneys; liver; lungs (including mainstem bronchi); lymph nodes - cervical ; lymph nodes - mesenteric; nasal cavity; oesophagus; pituitary gland; prostate gland; rectum; sciatic nerve; spinal column; spinal cord (cervical, thoracic, lumbar); spleen; stomach; thymus (where present); thyroid ; trachea; urinary bladder
- Reproductive organs / tissues preserved: epididymides; ovaries with oviducts; seminal vesicles with coagulating glands; testes; uterus - cervix; vagina.

GROSS PATHOLOGY: Yes
- Time schedule for examinations: Terminal sacrifice. All animals.
- Organs / tissues examined: All parent animals and pups wee examined macroscopically for any structural changes.
- Reproductive organs / tissues examined: Sexual organs were specifically examined. The number of implantation sites and corpora lutea was recorded for all dams with litters. The uteri of non-pregnant females were placed in a solution of ammonium sulfide to visualize possible hemorrhagic areas of implantation sites.

HISTOPATHOLOGY: Yes
- Time schedule for examinations: Tissues were collected from 5 males and 5 females (randomly selected) in the control and high dose group killed at terminal sacrifice and from all animals with abnormalities in all dose groups.
- Procedure: Tissues were dehydrated and embedded in paraffin wax, sections of the tissues were cut at 5 micrometer thickness and stained with haematoxylin and eosin. Testes and epididymides were cut at 2-3 micrometer thickness and stained with Periodic Acid Schiff (PAS) and morphological evaluation of the seminiferous epithelium (staging of spermatogenic cycle) was performed.
- Organs / tissues examined: all abnormalities; adrenal glands; bone marrow (from sternum); brain; caecum; colon; duodenum; heart; ileum; jejunum (including Peyer’s patches); kidneys; liver; lungs (including mainstem bronchi); lymph nodes - cervical ; lymph nodes - mesenteric; pituitary gland; prostate gland; rectum; sciatic nerve; spinal cord (cervical, thoracic, lumbar); spleen; stomach; thymus (where present); thyroid ; trachea; urinary bladder
- Reproductive organs / tissues examined: epididymides; ovaries with oviducts; seminal vesicles with coagulating glands; testes; uterus - cervix; vagina

ORGAN WEIGHT: Yes
- Time schedule for examinations: Organs were collected from all animals surviving the scheduled test period.
- Procedure: Organs were dissected free of fat and weighed. The ratios of organ weight to body weight were calculated for each animal.
- Organs / tissues examined: adrenal glands; brain; heart; kidneys; liver; prostate gland; spleen; thymus
- Reproductive organs / tissues examined: epididymides; ovaries with oviducts; testes
Postmortem examinations (offspring):
SACRIFICE
- The F1 offspring surviving to post partum Day 4 and pups killed or dying during the lactation period were sacrificed on post partum Day 4.
- These animals were subjected to postmortem examinations (macroscopic and/or microscopic examination) as follows:

GROSS NECROPSY
- All pups found dead in the cage were examined for external and internal abnormalities.
- All live pups sacrificed at termination were examined for external abnormalities.

HISTOPATHOLOGY / ORGAN WEIGHTS
Examinations not performed
Statistics:
- Standard deviations were calculated as appropriate. For continuous variables the significance of the differences amongst group means was assessed by Dunnett’s test or a modified t test, depending on the homogeneity of data.
- Statistical analysis of histopathological findings was carried out by means of the non-parametric Kolmogorov-Smirnov test if n was more than 5.
- The non-parametric Kruskal-Wallis analysis of variance was used for the other parameters. Intergroup differences between the control and treated groups were assessed by the non-parametric version of the Williams test.
- The criterion for statistical significance was p<0.05
Reproductive indices:
- The following reproductive indices were calculated: copulatory index; fertility index; pre-coital interval (mean number of days between pairing and mating); pre-implantation loss and pre-birth loss.
Offspring viability indices:
- The following viability indices were calculated: pup loss at birth and cumulative pup loss on Day 4 post partum.
Clinical signs:
no effects observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Organ weight findings including organ / body weight ratios:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
(toxicologically irrelevant)
Other effects:
no effects observed
Reproductive function: oestrous cycle:
no effects observed
Reproductive function: sperm measures:
no effects observed
Reproductive performance:
no effects observed
CLINICAL SIGNS AND MORTALITY
- No mortality occurred in the study.
- No clinical findings of toxicological significance were observed. Hair loss was occasionally recorded throughout the study including control animals. One female of the mid-dose group had salivation on Day 20 post coitum. One high dose female, that did not give birth, showed prolapse of the uterus on Day 27 post coitum. Another high dose female had rales during pairing.

BODY WEIGHT AND WEIGHT GAIN
- Body weight and body weight gain did not show relevant differences between groups. In particular, body weight gain was in some occasions higher in treated groups compared to the control group.

HAEMATOLOGY
- No changes of toxicological relevance were recorded.
- A statistically significant decrease of lymphocytes recorded in some females dosed with 300 mg/kg bw/day (42%) was not dose-related and, therefore, is considered incidental.
- No changes were observed in the coagulation test.

CLINICAL CHEMISTRY
- A number of males in the high dose group showed a slight decrease of protein and globulin (approximately 10%). Due to the low severity, these changes were considered of no toxicological importance.
- In addition, one animal showed high triglycerides (6.2 fold compared with controls). Due to the low incidence, this finding cannot be conclusively attributed to treatment; however, it also cannot be ruled out that it was related to treatment.

NEUROBEHAVIOUR
- Motor activity recorded at the end of treatment did not show significant differences between control and treated groups.

ORGAN WEIGHTS
- A slight significant reduction of epididymides weight occurred in the high-dose group; however, this reduction was found to be related to the higher terminal body weight in the high-dose group compared to controls. In addition, this change was minimal and no histological associated-findings were found. Therefore, it was considered of no toxicological relevance.

TERMINAL BODY WEIGHT AND ORGAN WEIGHTS
Body weight at term and organ weights did not show differences of toxicological relevance.

HISTOPATHOLOGY: NON-NEOPLASTIC
- Minimal, focal vacuolation of squamous epithelium (limiting ridge) of the non-glandular region of the stomach was observed was observed in the high and mid-dose males with an increased incidence in the high dose males and similar severity levels across treatment groups. However, as this gastric change was noted only in males, in a specific zone of the forestomach (limiting ridge) with focal and minimal severity and since humans do not have forestomach (squamous epithelium), such change could be considered toxicologically irrelevant.
- The remaining lesions reported in control and treated animals were considered to be an expression of spontaneous and/or incidental pathology, commonly seen in this species and age under our experimental conditions.

OTHER FINDINGS:
Spermatogenic cycle:
- A detailed qualitative examination of the testes was performed in control and high dose groups. The evaluation, taking into account the tubular stages of the spermatogenic cycle, was conducted in order to identify treatment-related effects, such as missing germ cell layers or types, retained spermatids, multinucleated or apoptotic germ cells and sloughing of spermatogenic cells into the lumen.
Seminiferous tubules were evaluated with respect to their stage in the spermatogenic cycle and to the integrity of the various cell types within the different stages; regular layering in the germinal epithelium was noted.

Oestrous cycle, reproductive parameters, pairing combination and mating performance:
No differences were found in the number of oestrous cycle, pre-coital intervals, copulatory and fertility indices between treated and control groups.

Implantation, pre-birth loss data and gestation length of females:
No significant differences were observed in the number of implantations, corpora lutea, total litter size, pre-implantation loss, pre-birth loss and gestation length between control and treated groups.
Key result
Dose descriptor:
NOAEL
Remarks:
(reproductive effects)
Effect level:
>= 1 000 mg/kg bw/day (actual dose received)
Based on:
act. ingr.
Remarks:
anhydrous zirconium acetate
Sex:
male/female
Basis for effect level:
other: Based on a lack of toxicologically relevant effects on reproductive organs/tissues or reproductive performance of parental animals.
Clinical signs:
no effects observed
Mortality / viability:
no mortality observed
Body weight and weight changes:
no effects observed
Sexual maturation:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
no effects observed
Histopathological findings:
not examined
CLINICAL SIGNS (OFFSPRING)
- Small pups were generally observed in all groups including the control group.
- Cold to touch and/or apparently no food intake were also occasionally recorded in all groups.
- One pup of low dose group showed absence of tail. This abnormality was considered incidental.

BODY WEIGHT (OFFSPRING)
- Mean pup weights were found comparable between groups at birth and on Day 4 post partum. Sex ratio did not differ between groups.

GROSS PATHOLOGY (OFFSPRING)
- The majority of decedent pups had autolysed organs in the abdominal cavity at necropsy.
- No abnormalities were found in pups sacrificed on Day 4 post partum with the exception of the low dose pup with the absence of tail. One pup of the mid-dose group showed no milk in stomach.

LITTER DATA AND SEX RATIOS:
Litter data including mean litter and pup weights were comparable between groups. No differences were found in sex ratio.
Key result
Dose descriptor:
NOAEL
Remarks:
(developmental effects)
Generation:
F1
Effect level:
>= 1 000 mg/kg bw/day (actual dose received)
Based on:
act. ingr.
Remarks:
anhydrous zirconium acetate
Sex:
male/female
Basis for effect level:
other: Based on a lack of developmental effects on pups in any dose group.
Key result
Reproductive effects observed:
no

Formulation

The overall results of the test formulation analyses were within the limits of acceptance for concentration (15% of the theoretical concentration).

Parameters

Reproductive parameters Group 1 (0 mg/kg bw/day) Group 2 (100 mg/kg bw/day) Group 3 (300 mg/kg bw/day)  Group 4 (1000 mg/kg bw/day)
 Pre-coital interval (days) 3.3  3.0   2.9  2.9
 Copulatory Index (%) 100.0 100.0 100.0  100.0
 Fertility index (%) 90.0 100.0 100.0 100.0 
 Gestation length (days) 21.88 22.10 22.0  22.11
 No. of pregnant females  9/10  10/10  10/10  10/10
 No. of non pregnant females  1/10 0/10 0/10   0/10
 No. of females with litter at birth  9/10  10/10  10/10  9/10
 No. of females with litter on Day 4 post partum  9/10 10/10 10/10  9/10 
 No. of pregnant females w/o litter  0/10  0/10  0/10  1/10

Litter data Group 1 (0 mg/kg bw/day) Group 2 (100 mg/kg bw/day) Group 3 (300 mg/kg bw/day)  Group 4 (1000 mg/kg bw/day)
Total litter size at birth 13.67 15.40  15.60 15.33
Live litter size at birth 13.67 15.20 15.50 15.22
Live litter size at Day 4 post partum 12.78 14.80 15.40 14.33 
Sex ratio at birth (% males) 57.76 58.54 49.05 55.53
Sex ratio on Day 4 post partum (% males) 58.01 59.62 49.60 59.98
Conclusions:
No effects on reproduction or development were observed in any dose group or in pups. Therefore, on the basis of the results obtained in the study, the No Observed Adverse Effect Level (NOAEL) for reproductive toxicity and for developmental toxicity was considered to be >=1000 mg/kg bw/day (expressed as zirconium acetate anhydrous).
Endpoint:
screening for reproductive / developmental toxicity
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Read across based on a study performed with zirconium acetate. The read across justification document is attached to IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Description (incidence and severity):
(toxicologically irrelevant)
Key result
Dose descriptor:
other: read across conclusion
Remarks on result:
other: Yttrium zirconium oxide was concluded not to cause adverse effects on reproduction.
Remarks:
Conclusion based on the results of a read across study performed with the water soluble zirconium compound zirconium acetate (Rossiello, 2013).
Key result
Critical effects observed:
no
Key result
Dose descriptor:
other: read across conclusion
Remarks on result:
other: Yttrium zirconium oxide was concluded not to cause any adverse effects on reproduction and development.
Remarks:
Conclusion based on the results of a read across study performed with the water soluble zirconium compound zirconium acetate (Rossiello, 2013).
Key result
Critical effects observed:
no
Key result
Reproductive effects observed:
no
Endpoint:
extended one-generation reproductive toxicity - basic test design (Cohorts 1A, and 1B without extension)
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because (i) the substance is of low toxicological activity (no evidence of toxicity seen in any of the tests available), (ii) it can be proven from toxicokinetic data that no systemic absorption occurs via relevant routes of exposure (e.g. plasma/blood concentrations below detection limit using a sensitive method and absence of the substance and of metabolites of the substance in urine, bile or exhaled air) and (iii) there is no or no significant human exposure
Reproductive effects observed:
not specified
Effect on fertility: via oral route
Endpoint conclusion:
no adverse effect observed
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

Effects on fertility: via oral route:

No information on the potential effects of yttrium zirconium oxide on reproduction is available. Because yttrium oxide, according to the read across justification attached to IUCLID Section 13, is not expected to affect the toxicological properties of zirconium dioxide (the main component in the crystal lattice of yttrium zirconium oxide), data on zirconium dioxide can be used for endpoint coverage. However, since no data on zirconium dioxide are available either, read across data are used from zirconium acetate, a water soluble zirconium compound, supported by the read across justification as included in the zirconium dioxide registration dossier.

Zirconium dioxide is an insoluble zirconium compound and therefore extremely low bioavailability is expected. Absorption factors of 10% have been proposed as worst case for oral, inhalation and dermal exposure although some evidence is available that this is a substantial overestimation.

The assessment of all the toxicological data identified for zirconium dioxide shows that this substance is of extremely low toxicological concern after acute and repeated exposure of test animals. Toxicological data from other zirconium compounds (both insoluble and 'water soluble') support the assumption that zirconium compounds are barely bioavailable and of extremely low toxicological concern.

In addition, so far, none of the zirconium compounds tested were shown to be mutagenic or clastogenic (zirconium dioxide, zirconium basic carbonate, zirconium acetate, zirconium sulfate, zirconium dichloride oxide) both in absence and presence of metabolic activation.

The results of a 60-day repeated dose toxicity study after inhalation exposure to zirconium dioxide (Spiegl et al., 1956) showed no abnormal findings after histopathological evaluation of animal testes. This supports the assumption that exposure to zirconium dioxide does not affect at least the male reproductive organs. Details on this study can be found in endpoint 7.5.

The systemic toxic effects of the read across substance zirconium acetate after repeated oral dosing, as well as any toxic effects on reproduction and development, were investigated in Sprague Dawley rats up to early lactation (day 4 post partum) by Rossiello (2013). The study was performed according to OECD guideline 422 and under GLP principles.

Three groups of 10 males and 10 females each received the test item, by oral gavage, at 100, 300 and 1000 mg anhydrous zirconium acetate/kg bw/day. A similar constituted control group received the vehicle alone during the treatment period. The overall dosing period was 32 days for males, which included 2 weeks before pairing and continuously thereafter up to the day before necropsy, and up to 50 days for females, including 2 weeks before pairing and thereafter during pairing, gestation and lactation periods until day 3 post partum.

The parental animals were followed for daily clinical signs, weekly body weight, food consumption, neurotoxicity assessment, oestrous cycle, mating performance, clinical pathology evaluation including haematology and clinical chemistry, and offspring delivery. A detailed macroscopic examination, determination of organ weights, and histopathological examination, including the spermatogenic cycle, were performed. Pups were also checked for sex, body weight, clinical signs and macroscopic observations.

No mortality occurred in the study. No treatment related findings were observed either during the in vivo phase or at post mortem examination of parent animals. Microscopically, a treatment related finding was seen in males receiving 300 and 1000 mg zirconium acetate/kg bw/day consisting of minimal focal vacuolation of squamous epithelium (limiting ridge) of the non-glandular region of the stomach. This change may be attributed to a local irritant effect of the compound administered by oral gavage and since humans do not have a forestomach or structural analogue to the forestomach, this finding is not considered of toxicological relevance. In addition, no abnormalities were found during the evaluation of the spermatogenic cycle. No treatment related effects were observed in the number of oestrous cycle, pre-coital intervals, copulatory and fertility indices between treated and control groups. No significant differences were observed in the number of implantations, corpora lutea, total litter size, pre-implantation loss, pre-birth loss and gestation length between control and treated groups.

No effects were noted on reproduction and development at any dose. On the basis of the results obtained in this study, the NOAEL for reproduction/developmental toxicity was considered to be >= 1000 mg/kg bw/day (expressed as anhydrous zirconium acetate), i.e., the highest dose tested.

Taking into account the concept of the more water soluble is the substance the higher is its potential for systemic bioavailability, it can be concluded that reproduction/developmental toxicity (if any) after repeated oral exposure to zirconium dioxide (an insoluble zirconium substance) will be of even lower concern than for zirconium acetate.

Annex IX further testing:

An OECD 422 test (Rossiello, 2013) has been performed according to GLP principles with the read across substance zirconium acetate, a 'water soluble' zirconium compound. Based on the lack of toxicologically relevant effects on reproductive organs/tissues or reproductive performance of parent animals, the NOAEL for reproductive/developmental toxicity was considered to be higher than or equal to 1000 mg/kg bw/day (the highest dose tested, expressed as anhydrous zirconium acetate). The results of this test (Rossiello, 2013) indicate that zirconium acetate is a substance of low toxicological concern for this endpoint.

Taking into account the concept that the more water soluble is the substance the higher is its potential for systemic bioavailability, it can be assumed that zirconium dioxide (an insoluble zirconium substance) will be of an even lower concern than zirconium acetate for reproduction. Evaluating available data on zirconium dioxide and other zirconium compounds, extremely low absorption and toxicity of zirconium dioxide is observed/expected. Therefore, no further testing (i.e., OECD 443) is deemed necessary for zirconium dioxide.

The same conclusion is reached for yttrium zirconium oxide, as yttrium oxide is, according to the read across justification attached to IUCLID Section 13, not expected to affect the toxicological properties of zirconium oxide. Therefore, no additional test is proposed for animal welfare reasons (e.g. OECD 443). The read across justification is added in Section 13 of IUCLID. The full justification for waiving based on all available data and expert judgement is similar as for further testing on developmental toxicity and is also attached to IUCLID Section 13.

Effects on developmental toxicity

Description of key information
No key experimental data are available on the developmental toxicity of yttrium zirconium oxide. Because yttrium (oxide) is, according to the read across justification attached to IUCLID Section 13, not expected to affect the toxicological properties of zirconium dioxide, the toxicological profile of yttrium zirconium oxide is expected to be similar to that of zirconium dioxide.
However, no data on developmental toxicity are available for zirconium dioxide either. Therefore, as in the zirconium dioxide registration dossier, all available data for zirconium dioxide as well as relevant information from other zirconium compounds (including the results of an OECD 422 study with the read across substance zirconium acetate, in which no adverse effects on developmental toxicity parameters were observed (Rossiello, 2013)), no testing is currently deemed necessary. The extended argumentation has been given in a document attached to IUCLID Section 13.
Link to relevant study records

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Endpoint:
developmental toxicity
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is of low toxicological activity (no evidence of toxicity seen in any of the tests available), it can be proven from toxicokinetic data that no systemic absorption occurs via relevant routes of exposure (e.g. plasma/blood concentrations below detection limit using a sensitive method and absence of the substance and of metabolites of the substance in urine, bile or exhaled air) and there is no or no significant human exposure
Species:
rabbit
Abnormalities:
not specified
Developmental effects observed:
not specified
Endpoint:
developmental toxicity
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because the substance is of low toxicological activity (no evidence of toxicity seen in any of the tests available), it can be proven from toxicokinetic data that no systemic absorption occurs via relevant routes of exposure (e.g. plasma/blood concentrations below detection limit using a sensitive method and absence of the substance and of metabolites of the substance in urine, bile or exhaled air) and there is no or no significant human exposure
Species:
rat
Abnormalities:
not specified
Developmental effects observed:
not specified
Effect on developmental toxicity: via oral route
Endpoint conclusion:
no adverse effect observed
Study duration:
subacute
Species:
rat
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

Developmental effects: oral route

In the read across justification document, it is concluded that the addition of yttrium (oxide) to the crystal lattice of zirconium dioxide does not alter the unhazardous properties of zirconium dioxide. Therefore, higher toxicological endpoints in this dossier are covered by information generated for zirconium dioxide. However, no key experimental information on developmental toxicity is available for yttrium zirconium oxide, zirconium dioxide, or any other zirconium compound. The results of the OECD 422 study performed with the read across substance zirconium acetate however offers supporting screening information.

Since the results of an OECD 422 study alone cannot be considered sufficient for waiving further testing on this endpoint, an assessment has been made based on all available (relevant) information on zirconium dioxide (an insoluble zirconium compound) and several other zirconium compounds (including both insoluble (zirconium basic carbonate) and 'water soluble' zirconium compounds (zirconium dichloride oxide, zirconium sulfate, zirconium acetate)). This evaluation has been presented in a document attached to IUCLID Section 13.

The following elements were considered to support the conclusion that further testing (prenatal developmental toxicity study) is not scientifically justified:

-Zirconium, whether from an insoluble or ‘water soluble’ zirconium compound, is extremely poorly soluble at environmentally and physiologically relevant pH levels.

-There is sufficient evidence indicating that zirconium is barely absorbed neither from the gastrointestinal tract nor after exposure via inhalation or contact with the skin and thus, the probability to reach the reproductive organs and the unborn offspring is considered to be extremely low.

-Zirconium compounds have a very low potential for causing toxicity, both acutely and long-term, and regardless of the route of exposure. Not much difference exists among the zirconium compounds considered in this evaluation, although there is some evidence (based on acute LD50 values) for ‘water soluble’ compounds to be slightly more toxic (may be due to the effect of the counter ions (acidification)). Read across from ‘water soluble’ to insoluble zirconium compounds therefore guarantees that the extrapolation is on the safe side.

-The available repeated dose toxicity studies did not report any adverse effects on specific organs (including reproductive organs), biochemistry, hematology, etc.

-So far none of the zirconium compounds tested has been found to be a genetic toxicant in vitro.

-An OECD 422 study with zirconium acetate did not reveal any adverse effects on reproduction or development of rats up to the highest dose tested (NOAEL >= 1000 mg anhydrous zirconium acetate/kg bw/d). This study can be extrapolated to zirconium dioxide.

-Due to the extremely low absorption and toxicity, it will be scientifically unjustified to perform a prenatal developmental toxicity study, since this study reasonably requires testing up to doses that cause maternal toxicity. Based on the evaluation and results mentioned above, it is considered acceptable to assume that effects on reproduction or development are not to be expected (if at all) at exposure levels well below the unbound values from the repeated dose toxicity studies.

-Finally, considerations on exposure were added to the argumentation (only occupational exposure, inhalation exposure never up to doses as high as the unbound NOAEC levels from the repeated dose toxicity studies – which are above the occupational exposure limits anyway, risk management measures advised in the guidance on safe use (local exhaust ventilation, respiratory protection), etc.).

The read-across justification is added in section 13 of IUCLID.

Justification for classification or non-classification

Based on all information available (OECD 422 test with zirconium acetate yielding a NOAEL >= 1000 mg/kg bw/day, and information on the toxicokinetic behaviour and the physicochemical and toxicological properties of zirconium dioxide and other relevant zirconium compounds) zirconium dioxide was concluded not be classified as toxic for reproduction. Zirconium substances appear to be poorly bioavailable and are of low (if any) toxicological concern since none of the available studies (short-term and long-term) so far have reported adverse effects. Since yttrium oxide is, according to the read across approach, not expected to alter the toxicological properties of zirconium dioxide, yttrium zirconium oxide can also be concluded not to be classified as toxic for reproduction.

Additional information