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Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
start: 2020-07-30 and still ongoing
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2021

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 413 (90-Day (Subchronic) Inhalation Toxicity Study
Version / remarks:
2018-06-25
Deviations:
yes
Remarks:
Ophthalmology not performed (this endpoint is not sensitive in particle studies); urine analysis not performed (endpoint optional only in guideline)
GLP compliance:
yes (incl. QA statement)
Remarks:
2018-11-22
Limit test:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Zirconium praseodymium yellow zircon
EC Number:
269-075-7
EC Name:
Zirconium praseodymium yellow zircon
Cas Number:
68187-15-5
Molecular formula:
Pr(x)Zr(1-x)SiO4 0,03≤x≤0,09
IUPAC Name:
Zirconium praseodymium yellow zircon
Test material form:
solid: particulate/powder
Details on test material:
- Name: Colorante amarillo
- EC Name: Zirconium Praseodymium Yellow Zircon
- Substance type: inorganic pigment
- Physical state: solid, yellow powder, odourless
- Storage condition of test material: at room temperature

Test animals

Species:
rat
Strain:
other: Crl:WI (Han)
Details on species / strain selection:
Wistar rats are commonly used in subchronic and chronic inhalation toxicity studies. They fulfil the criteria stated by a U.S. EPA Workshop (Vu et al., 1996)* such as (i) a low background rate of neoplasia, (ii) a low background rate of pulmonary disease, (iii) longevity, and (iv) a history of laboratory use.

*References:
- Vu, V., Barrett, J.C, Roycroft, J., Schuman, L., Dankovic, D., 1996. Workshop report: Chronic inhalation toxicity and carcinogenicity testing of respirable fibrous particles. Reg Tox Pharm 24, 202-212.
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Deutschland (Sulzfeld, Germany)
- Females nulliparous and non-pregnant: yes
- Age at study initiation: approx. 8 weeks
- Weight at study initiation: approx. 280 g for males and approx. 180 g for females
- Housing: housed in Makrolon (polycarbonate) cages type III with softwood (‘ssniff KB 8-15’) bedding material.
- Diet: commercial chow in pellet form (ssniff “V1534”) purchased from ssniff Spezialdiäten GmbH (Soest, Germany); ad libitum
- Water: tap water; ad libitum
- Acclimation period: Approx. one week the animals will be allowed to adjust and become acclimatised to the Fraunhofer ITEM environment. During the 2-3 weeks prior exposure start, all rats will be trained to the 6-hour restraint in nose-only tubes.

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 2°C
- Humidity: 55% ± 15%
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 2020-08-04 To: 2021-02-17

Administration / exposure

Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Vehicle:
air
Mass median aerodynamic diameter (MMAD):
>= 1.18 - <= 2.21 µm
Remarks on MMAD:
MMAD / GSD: please refer to Table 1 ('Any other information on materials and methods incl. tables')
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: flow-past nose-only inhalation exposure system
- Method of holding animals in test chamber: restrain tubes with a flexible stopper
- System of generating particulates/aerosols: The particulate sample aerosols were generated by dry dispersion with pressurized air. Cyclones (in line) were used to reduce the coarse moiety of the aerosol. For each nose-only exposure unit, the aerosol was generated by a high-pressure pneumatic disperser. The disperser was fed with the test/reference items under computerized control, i.e. with a feed back loop to the actual aerosol concentrations measured by an aerosol photometer. The photometer gives a scattering light signal which is proportional to the particle concentration, if the particle size distribution is constant. The ratio between photometer signal and concentration was determined throughout the study by comparing to gravimetric concentrations.
- Temperature, humidity, pressure in air chamber: Parameters were recorded by 20-minute means The were set at 22°C + 2°C for temperature and 55% + 15% for relative humidity.
- Air flow rate: 1 L/min
- Method of particle size determination: The MMAD was determined three to four times (once before exposure start and once per month during the exposure period for each test item exposure unit (3 units) by a cascade impactor (Marple impactor).
- Treatment of exhaust air: exhaled air is drawn off immediately by a cylinder surrounding the aerosol delivery cylinder

TEST ATMOSPHERE
- Brief description of analytical method used: Filter samples of the aerosols were taken daily to control the aerosol concentrations and to calibrate the aerosol photometers. The means are close to the target concentrations.
- Samples taken from breathing zone: yes
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
- see above ("Details on inhalation exposure")
- The target aerosol concentrations of 0.6, 2.5 and 10 mg/m³ Zirconium praseodymium yellow zircon were achieved exactly, i.e. to 100% in each group.
Duration of treatment / exposure:
13 weeks (65 exposure days)
Frequency of treatment:
6 hours/day, 5 days/week
Doses / concentrationsopen allclose all
Dose / conc.:
0.6 mg/m³ air (analytical)
Remarks:
SD: ± 0.08 mg/m³; 0.1 mg/lung (calculated total dose using MPPD v3.04)
Dose / conc.:
2.5 mg/m³ air (analytical)
Remarks:
SD: ± 0.38 mg/m³; 0.4 mg/lung (calculated total dose using MPPD v3.04)
Dose / conc.:
9.99 mg/m³ air (analytical)
Remarks:
SD: ± 0.94 mg/m³; 1.7 mg/lung (calculated total dose using MPPD v3.04)
No. of animals per sex per dose:
10+5 males and 10 females (1 day recovery); 5 males (28 days recovery); 5 males and females (90 days recovery) (total: 100 males and 60 females)
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: The concentrations were defined based on the preceding intratracheal instillation dose range finding (DRF A) study (Fraunhofer ITEM no. 02 N 20 502).
- Post-exposure recovery period: 1, 28, and 90 days

The nominal aerosol concentrations of 0.6, 2.5 and 10 mg/m³ were selected to achieve lung burden at the highest concentration that is at or above the lung overload conditions, i.e. impaired lung clearance. The test item deposition in the respiratory tract was modeled using the MPPD model (version 3.04), resulting in a deposited fraction of 4.7% (rel. density=5.1, MMAD/GSD=1.8 µm/1.5).
This deposited fraction was used to calculate the total deposited mass, using the following input parameters:
Morphometry: Semi-symmetric Long Evans
Example for deposited mass at 0.6 mg/m³: 0.2 l minute breathing volume x 360 min exposure/day x 65 exposure days x 0.6 mg/m³ x 4.7% = 0.13 mg/lung
Example for deposited mass at 2.5 mg/m³: 0.2 l minute breathing volume x 360 min exposure/day x 65 exposure days x 2.5 mg/m³ x 4.7% = 0.55 mg/lung
Example for deposited mass at 10 mg/m³: 0.2 l minute breathing volume x 360 min exposure/day x 65 exposure days x 10 mg/m³ x 4.7% = 2.2 mg/lung
Retained mass at 10 mg/m³: approx. 1.7 mg/lung
Positive control:
none

Examinations

Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: at least twice a day (with the exception of weekends and public holidays: once daily)

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: before sacrifice

BODY WEIGHT: Yes
- Time schedule for examinations: 1 day before treatment and twice a week in the first 4 and once a week thereafter throughout the study for all animals

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No
- Food consumption was determined for each group on a weekly basis.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Water consumption was determined for each group on a weekly basis.

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: 1 day after the 90-day exposure period
- Anaesthetic used for blood collection: No
- Animals fasted: No
- How many animals: 10 animals per sex and dose group
- Parameters examined: red blood cells (RBC), haemoglobin (HB), haematocrit (HCT), reticulocytes (RET), mean cell volume (MCV), mean haemoglobin/erythrocyte (MCH), mean haemoglobin concentration/erythrocyte (MCHC), prothrombin time (PT), thromboplastin time (TP), total white blood cells (WBC), differential white cell count (% and absolute), platelets (PTL)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: 1 day after the 90-day exposure period
- Animals fasted: No
- How many animals: 10 animals per sex and dose group
- Parameters examined: aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (AP), gamma-glutamyl transpeptidase (GGT), urea, triglycerides, total bilirubin, creatinine (CREA), total protein (TP), albumin (ALB), globulin (GLB), ALB/GLB, glucose (GLUC), cholesterol (CHOL), sodium (Na), calcium (Ca), potassium (K), phosphorous (P), chloride (CL)
URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

IMMUNOLOGY: No

BRONCHOALVEOLAR LAVAGE FLUID (BALF): Yes
- Time schedule for analysis: 1 and 90 days post-exposure
- Dose groups that were examined: all
- Number of animals: 5 (90 days post-exposure) - 10 (1 day post-exposure) per sex and dose group
- Parameters examined: total cell count, differential cell count (macrophages, neutrophils, eosinophils, lymphocytes; a total of 400 leukocytes per rat were evaluated), LDH, β-glucuronidase, and total protein

LUNG BURDEN: Yes
- Time schedule for analysis: 1, 28, and 90 after the 90-day exposure period
- Dose groups that were examined: all
- Number of animals: 5 male rats
Sacrifice and pathology:
- rats were sacrificed 1, 28, and 90 days after the 90-day exposure period
- macroscopic examination: all animals were subjected to a complete necropsy
- organ weights were determined for the following organs: liver, kidneys, adrenals, testes, epididymides, ovaries, uterus, thymus, spleen, brain, lung, and heart
- In the study the organs according to OECD guideline 413 were examined of the female and male animals of the clean air control and pigment 5 (Zirconium praseodymium yellow zircon) high dose group after 90 days nose-only inhalation.
These organs were as follows: adrenal glands, aorta, bone marrow (femur and sternum), brain (cerebrum, cerebellum, pons/medulla), coagulating glands, epididymis, esophagus, femur with knee joint, heart, intestine (duodenum, jejunum, ileum, cecum, colon, rectum), kidney, larynx, lung (left main lobe), liver, lymph nodes (lung-associated, mandibular, mesenteric), mammary gland, nasal cavity, olfactory bulb (in situ), ovaries, oviducts, pancreas, parathyroid glands, peripheral (sciatic) nerve, pituitary gland, prostate, salivary glands (mandibular, parotid, sublingual), seminal vesicles, skeletal muscle (biceps femoris), skin, spinal cord (cervical, thoracic and lumbar cords), spleen, stomach (forestomach and glandular stomach), testes, thymus, thyroid glands, trachea, urinary bladder, uterine cervix, uterus, vagina.
The following respiratory tract organs of animals 101-110 and 201-210 of group 1 and 4, respectively, were examined histopathologically: Nasal and paranasal cavities, pharynx (Laryngopharynx/nasopharynx), larynx, trachea, lung, lung-associated lymph nodes (LALN).
- All organs were preserved and fixed in formalin at day 1 and 90 post-exposure. Histopathology will be performed in 10 animals per sex of the control and high dose group at day 1 post-exposure. Additionally, histopathological examination of animals of both sexes of the low and intermediate dose group is included and still ongoing.
Statistics:
Differences between groups will be considered statistically significant at p < 0.05. Data will be analysed using analysis of variance. If the group means differ significantly by the analysis of variance, the means of the treated groups will be compared with the means of the control groups using Dunnett’s test. The statistical evaluation of the histopathological findings will be done with the two-tailed Fisher test by the PROVANTIS system.

Results and discussion

Results of examinations

Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
no effects observed
Ophthalmological findings:
not examined
Haematological findings:
effects observed, treatment-related
Description (incidence and severity):
In males, statistically significant dose-dependent increases were observed for segmented (SEGC) and banded (BANC) neutrophils (calculated values) and proportions of lymphocytes and segmented neutrophils in the mid and high dose groups (please refer to: 'Attached background material'):
- The SEGC was increased by +36.5% and +59.8% in males of the intermediate and high dose group, respectively. The proportion of segmented neutrophils was increased by +31.4% and +35.4% in the intermediate and high dose group, respectively.
- The BANC was increased by +75.8% in males of the high dose group.
- The proportion of lymphocytes was decreased by -8.1% and -10.8% in males of the intermediate and high dose group respectively.
Clinical biochemistry findings:
not specified
Description (incidence and severity):
Information will be added to the robust study summary upon availability
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
Absolute and relative lung wet weights resulted dose-dependently in statistically significant increases in the mid and high dose groups of both sexes (please refer to: ‘Attached background material’):
- Males: One day after the last exposure, males exposed to 2.5 and 10 mg/m³ showed an increase of +11.7% and +18.8% in absolute lung wet weight, respectively. The relative weight was increased by +7.5% in the intermediate dose group and by +15.8% in the high dose group. At post-exposure day 92, the absolute weight was found to be increased by +22.4% and +20.7% in males of the intermediate and high dose group, respectively. The relative weight was found to be increased (+22.5%) only in males of the high dose group.
- Females: One day after the last exposure, females exposed to 2.5 and 10 mg/m³ showed an increase of +14.8% and +23.7% in absolute lung wet weight, respectively. The relative weight was increased by +15% in the intermediate dose group and by +22% in the high dose group. At post-exposure day 92, females of the high dose group showed absolute and relative wet lung weights increased by +21.4% and +18.7%, respectively.
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
Upon necropsy, enlarged lung-associated lymph nodes (LALN) were observed dose-dependently in the mid and high dose groups of both sexes (please refer to: ‘Attached background material’). This is a particle-specific lung clearance pathway. Lungs showed typical dose-dependent discolourations caused by the test item.
- One day after the last exposure, the LALN were found to be enlarged in 1/20, 5/20, 16/20, and 17/20 males exposed to 0, 0.6, 2.5, and 10 mg/m³, respectively. In females of the control, low, intermediate, and high dose group the LALN were found to be enlarged in 2/10, 3/10, 9/10, and 10/10 animals, respectively. At post-exposure day 90, the LALN were enlarged in 0/5, 1/5, 4/5, and 5/5 males of the control, low, intermediate, and high dose group respectively. In females, the incidences were 0/5, 1/5, 5/5, and 5/5 in the control, low, intermediate, and high dose group, respectively.
- One day after the last exposure, the lungs showed discoloured areas in 0/20, 6/20, 4/20, and 4/20 males exposed to 0, 0.6, 2.5, and 10 mg/m³, respectively. In females of the control, low, intermediate, and high dose group the lungs showed discoloured areas in 1/10, 3/10, 2/10, and 3/10 animals, respectively. At post-exposure day 90, the lungs showed discolouration in 0/5, 2/5, 1/5, and 2/5 males of the control, low, intermediate, and high dose group respectively. In females, the incidences were 0/5, 1/5, 0/5, and 1/5 in the control, low, intermediate, and high dose group, respectively.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Findings related to the inhalation of the test item were detected within the lung, the nasal cavity, and the lung-associated lymph nodes.

- Animals exposed to 0.6 mg/m³:
• In the lung, exposure-related findings represent very slight multifocal particle-laden macrophages in the alveoli in 10/10 males and 10/10 females.
• In the lung-associated lymph nodes (LALN), there was a very slight multifocal accumulation of particle-laden macrophages in 3/10 males and in 2/10 females.

- Animals exposed to 2.5 mg/m³:
• In the lung, exposure-related findings represent very slight multifocal granulocytic cell infiltration in the alveoli in 10/10 male and 9/10 female rats. In addition, in the lung alveoli, very slight multifocal extracellular material was seen in 2/10 female rats. This extracellular material appeared eosinophilic partially granular and was interpreted to be consisting of cell debris and surfactant admixed with particles. Particle-laden macrophages were observed multifocally in the alveoli in 10/10 males (all slight) and 10/10 females (all slight) as well as in the bronchus-associated lymphoid tissue in 5/10 males (3 very slight; 2 slight) and in 6/10 females (5 very slight; 1 slight). This lesion correlated with a macroscopically observed dark grey multifocal discoloration of up to 1mm in diameter in the lung. Further in the lung interstitium, there was a multifocal very slight mixed inflammatory cell infiltration in 2/10 males and in 2/10 females. This interstitial inflammatory cell infiltration was mainly observed in the vicinity of the terminal bronchi. A multifocal very slight bronchiolo-alveolar hyperplasia of the bronchial type (bronchiolization) was seen in 1/10 females.
• In the nasal cavity, a very slight multifocal accumulation of particle-laden macrophages was found in 3/10 males and 3/10 females in the nose-associated lymphoid tissue (NALT).
• In the lung-associated lymph nodes (LALN), there was a multifocal accumulation of particle-laden macrophages in 8/10 males (5 very slight; 3 slight) and in 9/10 females (3 very slight; 6 slight). In addition, 3 males (2 very slight; 1 slight) and 2 females (1 very slight; 1 slight) showed a diffuse increased cellularity of lymphocytes.
• These lesions correlated with a macroscopically observed enlargement and greenish discoloration in many animals.

- Animals exposed to 10 mg/m³:
• In the lung, exposure-related findings represent very slight multifocal granulocytic cell infiltration in the alveoli in 9/10 male and 10/10 female rats. In addition, in the lung alveoli, very slight multifocal extracellular material was seen in 7/10 male and 10/10 female rats. This extracellular material appeared eosinophilic partially granular and was interpreted to be consisting of cell debris and surfactant admixed with particles. Particle-laden macrophages were observed multifocally in the alveoli in 10/10 males (all slight) and 10/10 females (1 very slight; 8 slight; 1 moderate) as well as in the bronchus-associated lymphoid tissue in 10/10 males (7 very slight; 3 slight) and in 9/10 females (6 very slight; 3 slight). This lesion correlated with a macroscopically observed dark grey multifocal discoloration of up to 1 mm in diameter in the lung. Further in the lung interstitium, there was a multifocal mixed inflammatory cell infiltration in 3/10 males (all very slight) and in 5/10 females (4 very slight; 1 slight). This interstitial inflammatory cell infiltration was mainly observed in the vicinity of the terminal bronchi. A multifocal very slight bronchiolo-alveolar hyperplasia of the bronchial type (bronchiolization) was seen in 2/10 males and 2/10 females.
• In the nasal cavity, a very slight multifocal accumulation of particle-laden macrophages was found in 3/10 males and 4/10 females in the nose-associated lymphoid tissue (NALT).
• The occurrence of very slight multifocal hyaline droplets in 2 females was considered to be unrelated to the exposure.
• In the lung-associated lymph nodes (LALN), there was a multifocal accumulation of particle-laden macrophages in 9/10 males (4 slight; 5 moderate) and in 10/10 females (4 slight; 6 moderate). In addition, 3 males (2 very slight; 1 slight) and 5 females (2 very slight; 3 slight) showed a diffuse increased cellularity of lymphocytes.
• These lesions correlated with a macroscopically observed enlargement and greenish discoloration in many animals.

Please refer to: ‘Attached background material’ for statistical intergroup comparison and detailed listing.
Histopathological findings: neoplastic:
no effects observed
Other effects:
effects observed, treatment-related
Description (incidence and severity):
BRONCHOALVEOLAR LAVAGE FLUID (BALF):
- At days 1 and 90 post-exposure, statistically significant and dose-dependent increases of polymorphonuclear neutrophils (PMN) were detected in the mid and high dose groups. The PMN percentages (29% and 42%, males - 29% and 30%, females in the mid and high dose groups, respectively) demonstrate a moderate inflammatory potential as compared to clean air control data (3-4% PMN).
- At day 90 post-exposure, for lactic dehydrogenase, ß-glucuronidase and total protein statistically significant and dose-dependent increases were detected in the mid and high dose groups of both sexes; after 90 days of recovery, however, still statistically significant increases were observed in the mid and high dose group of females.
• Lactic dehydrogenase activity: At day 1 post-exposure, lactic dehydrogenase activity was 2.0- and 2.9-fold increased in the male intermediate and high dose group, respectively. In females, the lactic dehydrogenase activity was 2.6- and 3.2-fold increased, respectively. At post-exposure day 92, females of the intermediate and high dose group showed a 1.9- and 2.4-fold increased lactic dehydrogenase activity, respectively.
• ß-glucuronidase activity: At day 1 post-exposure, the ß-glucuronidase activity was 2.5- and 5.0-fold increased in males of the intermediate and high dose group, respectively. In females, the ß-glucuronidase activity was 2.9- and 4.2-fold increased over controls. At post-exposure day 92, females of the intermediate dose group showed a 2.4-fold increase above controls, while the high dose group showed a 3.9-fold increased ß-glucuronidase activity.
• Total protein concentration: At day 1 post-exposure, the total protein concentration was 1.7- and 2.3-fold increased in the male intermediate and high dose group, respectively. In females, the total protein concentration was 1.9- and 2.4-fold increased, respectively. At post-exposure day 92, females of the intermediate and high dose group showed a 1.7- and 2.0-fold increased total protein concentration as compared to the control group.

- Lung weights (BAL): In both sexes, statistically significant increases were observed in the mid (+7.5% and +15% in males and females, respectively, at post-exposure day 1) and high dose (+15.8% and +22% in males and females, respectively, at post-exposure day 1; +18.7% in females at post-exposure day 92) groups.

LUNG BURDEN ANALYSIS:
- The absolute lung weight was statistically significantly increased in males of the intermediate dose group at post-exposure day 92 (+22.4%) as well as in males of the high dose group at post-exposure day 1, 28 and 92 (+22.6%, +20.2%, and +20.7%, respectively). The relative lung weight was statistically significantly increased in males of the high dose group at post-exposure days 28 and 92 (+24.4% and +22.5%, respectively).
- The results of the chemical lung burden analysis will be submitted later.
Details on results:
MORTALITY:
Rat #9122 (female of the intermediate dose group) died spontaneously (day 77) and was preserved for histopathological examination. It showed macroscopically a dark red 5 mm in diameter sized focus in the right hemisphere of the brain. This correlated histologically with a focal severe vascular hamartoma and a focal acute moderate hemorrhage into the brain parenchyma. These lesions are interpreted to be the cause of death of this animal and represent a developmental disorder without any relation to the exposure.

BODY WEIGHT AND WEIGHT CHANGES:
Relevant statistically significant changes were not observed in the treatment groups as compared to concurrent controls.

WATER CONSUMPTION:
- Some observed statistically altered values were considered as incidental findings as these effects were without a clear dose-dependency.

GROSS PATHOLOGY:
- Other test item- or dose-related macroscopical findings were not detected. Only some incidental macroscopic observations were obtained (please refer to: ‘Attached background material’).

ORGAN WEIGHT FINDINGS INCL ORGAN / BODY WEIGHT RATIOS:
- Incidental increases were observed in the absolute (+26.8%) and relative (+23.1%) thymus weight of males exposed to 2.5 mg/m³ immediately after the last exposure. On post-exposure day 1, the left ovaries, of females exposed to 0.6 mg/m³, showed an absolute increase of +21% as well as an absolute and relative increase of +25.5% and +25.7%, respectively, in females exposed to 2.5 mg/m³. On post-exposure day 1, the relative uterus weight, of females exposed to 10 mg/m³, was decreased by -28.3%. Moreover, at post-exposure day 92, females exposed to 0.6 mg/m³ showed increased absolute weights of the left adrenal (+49.7%) and lung (+18.4%) as well as a decrease in the relative weight of the thymus (-21.3%). These alterations were only slight in magnitude, not consistent within/between animals, not dose-dependent, and without histopathological correlates. Thus, these effects are considered to be incidental and without toxicological relevance.

HAEMATOLOGICAL FINDINGS:
- In both sexes, no relevant statistically significant changes as compared to concurrent controls.
- The thromboplastin time was statistically significantly decreased by -8.2%, -7.0%, and -10.6% in males exposed to 0.6, 2.5, and 10 mg/m³, respectively. However, the change is only very slight and considered to be not toxicologically relevant.

HISTOPATHOLOGICAL FINDINGS: NON-NEOPLASTIC:
- Clean air control group: In one animal of the control group, a lymphoma of the hematolymphoid system with infiltration of lymphoma cells into the bone marrow, liver, lung-associated, mandibular and mesenteric lymph nodes, and spleen was observed. This correlated with macroscopically observed enlarged spleen and lung-associated lymph nodes. In addition, single lesions were seen in different other organs, which represented commonly found background lesions in this rat strain.
- All the other findings within the different organs occurred in single animals and were interpreted to be incidental without any relation to the exposure.
- Animals exposed to 0.6 mg/m³: In the nasal cavity and trachea no lesions were seen.

Effect levels

Remarks on result:
not determinable
Remarks:
The NOAEC will be derived upon completeness of the data set.

Target system / organ toxicity

Critical effects observed:
no

Applicant's summary and conclusion

Conclusions:
In this 90-day repeated dose toxicity by inhalation study, rats were exposed via nose-only inhalation towards aerosol concentrations of 0.6, 2.5 and 10 mg/m³ of zirconium praseodymium yellow zircon.
All animals (but one sudden death) survived the test period and were euthanized at scheduled dates. Effects indicating systemic toxicity were not observed.
Sex-specific differences were not detected.
No relevant statistically significant changes as compared to concurrent controls were observed for: Body weight and body weight development, haematology, food and water consumption.
The lung weights were statistically significantly increased in the mid and high dose groups. The BALF analyses revealed persistent, statistically significant and dose-dependent increases of polymorphonuclear neutrophils (PMN) in the mid and high dose groups, demonstrating, based on the effect magnitude, a moderate inflammatory potential. Moreover, the lactic dehydrogenase activity, ß-glucuronidase activity and total protein concentration were persistently, statistically significantly and dose-dependently increased in BALF of the mid and high dose groups of both sexes. Adverse findings, as revealed via histopathological examination, representing very slight alveolar granulocytic cell infiltration, very slight alveolar extracellular material and very slight to slight interstitial mixed inflammatory cell infiltration, were detected within the investigated zirconium praseodymium yellow zircon high dose group and partially (very slight alveolar granulocytic cell infiltration) in the mid dose group. In the low dose group, no adverse findings were detected.

The NOAEC will be derived upon completeness of the data set.

The measures implemented during the ongoing Covid-19 pandemic lead to a delay in laboratory capacities and delays in the study conduct. Due to this, the following parameters are not yet available and will be added to the robust study summary upon availability:
(i) chemical analysis of lung burden
(ii) clinical chemistry
(iii) QAU evaluation and study finalisation

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