Yttrium oxide

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

other: Published results

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

This publication described a 30 days repeated inhalation study of yttrium oxide on dogs and is fully described with respect to the experimental conditions and the results. However, the GLP are not stated and there is no reference to international guideline.

Data source

Reference

Reference Type:

publication

Title:

Effect of inhaled yttrium oxide on blood lactic acid, erythrocyte volume, and histologic features of lungs in exercised dogs

Author:

Reece W.O., Talbot R.B., Swenson M.J.

Year:

1967

Bibliographic source:

Am. J. vet. Res., Vol. 28, N° 125

Materials and methods

Principles of method if other than guideline:

18 beagles dogs were subjected to treadmill exercise and exposure to a chamber atmosphere of yttrium oxide. The exposure lasted 30 days (180 exposure hours) and treadmill exercise was given for 10 minutes a day throughout the experiment. Postexercise value of blood lactate concentration was determined 2 times a week and erythrocyte volume, plasma volume, hemoglobin concentration and leukocyte count were determined before the start and at the end of the exposure period.
Thoracic radiographs were done before the exposure to determine freedom from lung lesions and subsequent fitness for treadmill exercise.
Histologic examination was done on dogs after exposure period. Aerosol concentration, distribution and particles size have been determined.

GLP compliance:

not specified

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Yttrium oxide

EC Number:

215-233-5

EC Name:

Yttrium oxide

Cas Number:

1314-36-9

Molecular formula:

O3Y2

IUPAC Name:

diyttrium(3+) trioxidandiide

Details on test material:

The substance was guaranteed 99.9 % pure. Generation of the aerosol was accomplished with a Wright dust feed mechanism.
The mean particles size diameter was: 0.393 +/- 0.345 µm.
The final concentration for the experiment was between 12.65 +/- 5.04 and 20.63 +/- 3.03 µm/m3.

Test animals

Species:

dog

Strain:

Beagle

Sex:

male/female

Details on test animals or test system and environmental conditions:

3 separate experiments with 8 dogs (4 males and 4 females), 6 to 9 months, were used. The dogs were vaccined against canine distemper, infectious hepatitis and lesptospirosis, given a physical examination and treated for internal parasitic infestation. A negative result was obtained on the examination for Dirofilaria. A commercial dry dog feed was reasonably fed according to the recommendation of the manufacturer and water was available ad libitum.

The dogs were trained (4 to 5 weeks) to run on a treadmill before the 10-week experiment. Each dog was exercised on the treadmill for 10 minutes daily, each 5 days a week in a room maintained at 22 - 23 °C. The dogs were placed in individual cages, placed in a chamber environment each afternoon for 6 hours, 5 days a week for the 10-week experiment.

Administration / exposure

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Vehicle:

air

Remarks on MMAD:

MMAD / GSD: 0.393 +/- 0.345 µm

Details on inhalation exposure:

Preparation of aerosol:
The original pulverized powder of yttrium oxide (99.9 %) was reduced to a uniform particles size in a blender. Generation of the aerosol was accomplished with a Wright dust feed mechanism. Its operation was dependent on the removal, by a stream of air, of dust as it was scraped from a revolving cylinder tightly packed with yttrium oxide.

Exposure method:
While in the chambers the dogs were confined to individual cage were made with stainless steel, the top, bottom, sides and ends were constructed of expanded stainless steel fabric which permitted free passage of air.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

During the experiment three kind of controls were performed: particles size determination, aerosol distribution and mass distribution of the aerosol.
Particle Size determination: the chamber atmosphere was sampled with a point-to-plane electrostatic precipitator. The maximal diameter was analyzed by an electron photomicrograph with a particle size analyzer.

Aerosol concentration: the concentration of yttrium oxide during the exposure period was arbitrarily set at 15 mg/cu.m. To maintain this concentration, daily sampling was required and adjustments were made accordingly. A color-forming reagent was used for the quantitative determination of yttrium and rare earths concentration (according to Fritz et al.).

Mass distribution of aerosol: a Casella cascade impactor was used to determine the mass distribution of aerosol and the percentage of particles less than 1 µm. When distribution samples were collected, glass coverslips coated with stopcock grease were affixed to the stages. A filter retained particles not impinged at the stages. Samples were collected for 30 seconds. The size of the particles collected on the various stages was determined by electron microscopy. Electron microscopy girds were mounted in the line of deposition at each stage and particles were impinged directly on these girds and measured.

Duration of treatment / exposure:

The dogs were trained (4 to 5 weeks) to run on a treadmill before the 10-week experiment. Each dog was exercised on the treadmill for 10 minutes daily, each 5 days a week in a room maintained at 22 - 23 °C. The dogs were placed in individual cages, placed in a chamber environment each afternoon for 6 hours, 5 days a week for the 10-week experiment.
The dogs were in paired experiment in which the first 4 weeks comprised the control period and the next 6 weeks, the treatment period.

Frequency of treatment:

6 hours a day, 5 days a week during 6 weeks.

No. of animals per sex per dose:

Three groups of six dogs (male and female) were treated with the enclosed measured concentrations (expressed in mg Y2O3/m3) :
exp 8A: 20.63 +/- 3.03
exp 8B: 12.65 +/- 5.04
exp 8C: 16.88 +/- 3.88

Control animals:

yes, concurrent no treatment

Details on study design:

The dogs were trained (4 to 5 weeks) to run on a treadmill, then, the 10-week experiment was started. Each dog was exercised on the treadmill (between 10:00 and 12:00 a.m.) for 10 minutes daily for 5 days a week. The exercising was accomplished in a room where the temperature was maintained at 22 to 23°C. The dogs were placed in individual cages and the cages were placed in a chamber environment each afternoon for 6 hours, 5 days a week for the 10-week experiment.

The dogs were in a paired experiment in which the first 4 weeks comprised the control period and the next 6 weeks, the treatment period. During the control period, increases in receptivity and running ability were noticed. Also a treadmill speed was set for each dog in two groups of six dogs that appeared to obtain satisfactory work output and that correlated with a plateau of blood lactate concentration. In the third group of dogs, they were exercised at the same treadmill speed and it became apparent that the running abilities were not equal. Establishing a lactic acid plateau seemed logical in that any blood lactate increase which might be observed later would be relative to previous level.
With this design it was possible to establish normal values before yttrium oxide was introduced and to obtain a series of observations during the inhalation or treatment period.
The various responses could then be expressed as « change » over the treatment period. To provide for histologic comparisons, 1 male and 1 female dog from each group of 8 were placed in chambers in which yttrium oxide was not introduced during the 6 weeks treatment. The 2 dogs never became good runners and tended to hang back in the harness. Because of their poor performance, the corresponding blood lactate concentration and other values relative to exercise were not meaningful.

Positive control:

No data

Examinations

Observations and examinations performed and frequency:

Several analysis have been realised after the exposure period:

1. Post exercise blood lactate concentration, obtained 2 times a week during the experiment
2. Erytrocyte volume measurement was performed on each dog before and after the end of the experiment.
3. Plasma Volume for each dog was determined before and at the end of the exposure period.
4. Other hematologic values: Leukocyte counts, packed cell volume and total hemoglobin concentration were determined before and at the end of the experiment.
5. Radiographic examination of thorax on each dogs were made before and at the end of the exposure period.
6. Necropsy was realised after the end of each experiment.

Sacrifice and pathology:

6. Necropsy
After the end of each experiment the dogs were euthanatized and necropsied. Portion of sternum, lungs, heart, liver, spleen, adrenal gland, kidneys, bronchial lymph nodes, gonad and mesenteric lymph nodes were obtained for histologic examination. These tissues were fixed in 10 M formalin and paraffin sections were cut at a thickness of 6 µm and stained with hematoxin-eosin stain

Other examinations:

1. Post exercise blood lactate concentration, obtained 2 times a week during the experiment
5 ml of blood was withdrawn from the right and left jugular vein approximately 30 sec after the treadmill exercise. The blood was withdrawn in a syringe containing crystalline ammonium fluoride to avoid coagulation.
The same day, the lactate concentration was determined by the method of Barker and Summerson.

2. Erythrocyte volume measurement
The erythrocyte volume of each dog was determine before and after the end of the experiment, using Na2CrO4 which is a modification of Sterling and Grey. Radioactivity was determined in a well-type, thallium actived NaI crystal scintillation counter.

3. Plasma Volume measurement
Plasma volume for each dog was determined before and at the end of the exposure period by a modification of the T-1824 dye dilution method of Gregerson as already described in the literature.

4. Other hematologic values
Leukocyte counts, packed cell volume and total hemoglobin concentration were determined before and at the end of the yttrium oxide exposure.

5. Radiographic examination of thorax
Thoracic radiographs of each dogs were made before and at the end of the exposure period to determine freedom of lung lesions and subsequent fitness for treadmill exercise. The occurrence of any increase in radiographic density due to the exposure was also observed.

Statistics:

The Student's test was used to determine the relevance of observed difference after exposure and/or exercise. A variance test was also conducted to determine any difference due to the sex of dogs.

Results and discussion

Results of examinations

Clinical signs:

not specified

Mortality:

not specified

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

No effect on plasma volume & hemoglobin concentration. Significant increase of white blood cells & decrease of the erythrocyte volume which should indicated Y2O3 was being transported from the lungs to other tissues, having negative erythropoiesis effect.

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

not specified

Details on results:

Histologic examination showed no effect on: heart, liver, spleen, mesenteric lymph nodes, testis or ovaries, kidneys, adrenal gland, and bone marrow.
Toraxic radiography showed subtle changes which are consistent with the slightly increased density at the hilus of the lung. Possibly the enlarged bronchial lymph nodes which contained numerous dust laden macrophages contributed to the slight increase in density.

Blood lactate concentration:
This parameter was obtained by subtracting a normal value before the exposure and after 30 days of exposure for the same dog.
Normal value was determined as the average of results for 4 determinations (2 made during the week before exposure and 2 during the weeks after exposure began).
The mean of the difference was + 5.00 mg/100 mL of blood. This difference was tested as relevant according to the Student’s test. It was assumed that, with repeated treadmill exercise under conditions of no exposure, post exercise blood lactate concentration would decrease. This decrease was demonstrated by Yoder and al.
A variance analysis showed no significant difference due to replication of test or sex of dog.

A highly positive increase occurred in 3 dogs, 1 from each experiment which indicated that some alteration had occurred in their ability to transfer, transport or utilize oxygen. Toward the end of the experiment, it became difficult to these dogs to complete their 10-minute exercise period. It was observed that certain dogs respond to treadmill exercising quite favorably, whereas others are more reluctant to increase work output. In an ideal situation only dogs responding favorably should be selected and subjected to a greater work task.

Erythrocyte volume: The overall mean of the difference was 3.9 mL/kg of body weight and was only significant at the 0.10 level. No difference was observed regarding replication or sex. The mean of this difference was negative. One might assume that with increased tissue demands for oxygen an increase in erythrocyte volume might occur. It is possible that enough yttrium oxide was being transported from the lungs to other tissues to have an inhibiting effect upon erythropoiesis. One might have observed a more significant decrease in erythrocyte volume if the period of exposure and exercise had been extended.

Plasma volume and hemoglobin concentration: the mean of the differences were no significant.

Leukocyte count: The overall mean of the difference is 2.333 leucocytes/cm3 of blood. This was significant increase an active response of the body the remove foreign material. Regarding the absence of difference observed in white blood cell counts by Davison if mice and guinea pigs were exposed to dust aerosols of neodymium, this result could be a peculiarity of species response.
A slightly significant decrease in circulating monocytes was seen at the end of the exposure period. This was significant at the 0.10 level.
No significant change in distribution of other white blood cell types was detected.

Necropsy results:
Lungs of exposed dogs were reddish grey instead of pink. Bronchial lymph nodes in exposed dogs were enlarges 8 to 10 times but other body lymph nodes were normal in size. With regards to gross appearance, all other organs were normal.

Results of histologic examination:
Many cellular elements were within the alveoli of lungs of exposed dogs. The most apparent histologic change occurring as a result of 30 day’s exposure to yttrium oxide was the presence of many macrophages and leukocytes in the alveaoli. According to Hatch & gross, these alveolar macrophages or “dust cells”. The extreme hypertrophy of alveolar epithelial cells prior to desquamation is shown.
The leukocytes were mainly neutrophils. Many had elongated nuclei and were nuclei and were probably in the process of diapedesis. Seemingly, a leukotactic substance was attracting many leucocytes to the lungs and this was reflected by the increases leukocyte count.
Examination of the lungs indicated no connective tissue increase.

Results of examination of bronchial lymph nodes from expected dogs indicated the presence of many dust-laden macrophages. These macrophages were seen after 30 days of exposure.

Radiographic examination: slight increase of the lung density probably due to the increase of dust-laden macrophages.

Effect levels

Dose descriptor:

NOEL

Effect level:

> 20.63 mg/m³ air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No systemic toxicity

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

No relevant systemic effects were observed during this study, exposing dogs 30 days to 20.63 mg Y2O3/m3.
However, an overall NOEL could be established to be above 20.63 mg/m3, based on the absence of change in hematology, organ weights, macroscopic observations at necropsy and histopathology at the tested concentration.

No classification for repeat-dose toxicity is warranted based on the absence of toxicologically relevant effects in this study, according to the criteria of Annex VI Directive 67/748/EEC or the 1272/2008 regulation -CLP).

Executive summary:

- Gross Pathology: No effect

- Histopathology: no effect on hearth, liver, spleen, mesenteric lymph nodes, testis or ovaries, kidneys, adrenal gland and bone narrow

- Thoracic radiographs of each dog were made before and at the end of the exposure period to determine freedom of lung lesions and subsequent fitness for treadmill exercise. No relevant effect.

- Lungs exposed dogs were reddish gray and were firmer than the lungs of the controls. Bronchial lymph nodes in exposed dogs were enlarged 8 - 10 times; other body lymph nodes were normal in size. With regards to gross appearance, other organs were normal.

- Effect on plasma volume & hemoglobin concentration. Significant increase of white blood cells, dust-laden macrophages in the bronchial lymph nodes & decrease of the erythrocyte volume which should indicated Y2O3 was being transported from the lungs to other tissues, having negative erythropoiesis effect.

The observed effects were rather consistent with a local inflammatory response of lung following inhalation of poorly soluble particles of low toxicity, with no systemic effects and a limited relevance to the human occupational situation given the levels of exposure.