Dierbium trioxide

Acute Toxicity: inhalation

Administrative data

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 August 2012 - 20 September 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study conducted to GLP in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 436 (Acute Inhalation Toxicity: Acute Toxic Class Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

acute toxic class method

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Dierbium trioxide

EC Number:

235-045-7

EC Name:

Dierbium trioxide

Cas Number:

12061-16-4

Molecular formula:

Er2O3

IUPAC Name:

dierbium(3+) trioxidandiide

Test material form:

solid: particulate/powder

Details on test material:

Appearance: pink powder
Storage conditions: room temperature, in the dark

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Strain: RccHan:WIST
- Age at study initiation: approximately 8 - 12 weeks
- Weight at study initiation: 200 - 350 g
- Fasting period before study: no
- Housing: The animals were housed in groups of up to three by sex in solid-floor polypropylene cages with stainless steel lids, furnished with softwood flakes and provided with environmental enrichment items: wooden chew blocks and cardboard “fun tunnels”.
- Diet: With the exception of the exposure period, free access to food was allowed.
- Water: ad libitum with the exception of the exposure period.
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19 - 25 °C
- Humidity (%): 30 - 70 %
- Air changes (per hr): at least 15 per hour
- Photoperiod (hrs dark / hrs light): the lighting was controlled to give twelve hours continuous light and twelve hours darkness.

Administration / exposure

Route of administration:

inhalation: dust

Type of inhalation exposure:

nose only

Vehicle:

clean air

Details on inhalation exposure:

ATMOSPHERE GENERATION
In order to facilitate aerosolisation and reduce particle size, the test material was ground using a small amount of diethyl ether in a Retsch Planetary Ball Mill (Retsch (UK) Ltd., Leeds, UK). The solvent was removed via evaporation prior to use.
A dust atmosphere was produced from the test material using an SAG 410 Solid Aerosol Generator (TOPAS GmbH, Dresden, Germany) located adjacent to the exposure chamber. The SAG 410 was connected to a metered compressed air supply.
Compressed air was supplied by means of an oil free compressor and passed through a water trap and respiratory quality filters before it was introduced to the SAG 410.
The cylindrical exposure chamber had a volume of approximately 30 litres (dimensions: 28 cm diameter x 50 cm high). The concentration within the chamber was controlled by adjusting the test material feed rate from the SAG 410. The extract from the exposure chamber passed through a ‘scrubber’ trap and was connected with a high efficiency filter to a metered exhaust system. The chamber was maintained under negative pressure.

Prior to the start of the study, test material atmospheres were generated within the exposure chamber. During this characterisation period test material input rates and the generation system were varied in order to achieve the required atmospheric conditions.


EXPOSURE PROCEDURE
Prior to the day of exposure each rat was acclimatised (for approximately 2 hours) to a tapered polycarbonate restraining tube. During the day of exposure, each rat was individually held in a tapered, polycarbonate restraining tube fitted onto a single tier of the exposure chamber and sealed by means of a rubber ‘O’ ring.
A target concentration of 5.0 mg/L was used for the exposure. The mean achieved concentration was 102 % of target.


EXPOSURE CHAMBER TEMPERATURE AND RELATIVE HUMIDITY
The temperature and relative humidity inside the exposure chamber were measured by an electronic thermometer/humidity meter (Hanna Instruments Ltd, Beds., UK) located in a vacant port in the animals’ breathing zone of the chamber and recorded every thirty minutes.


EXPOSURE CHAMBER OXYGEN CONCENTRATION
Oxygen levels within the exposure chamber were measured by an electronic oxygen analyser (Servomex (UK) Ltd, Crowborough, East Sussex) located in a port in the animals’ breathing zone. The test atmosphere was generated to contain at least 19 % oxygen.


EXPOSURE CHAMBER ATMOSPHERE CONCENTRATION
The actual chamber concentration was measured at regular intervals during the exposure period. The gravimetric method used glass fibre filters placed in a filter holder. The holder was temporarily sealed in a vacant port in the exposure chamber in the animals’ breathing zone and a suitable, known volume of exposure chamber air was drawn through the filter using a vacuum pump.
Each filter was weighed before and after sampling in order to calculate the weight of collected test material. The difference in the two weights, divided by the volume of atmosphere sampled, gave the actual chamber concentration.
The nominal chamber concentration was calculated by dividing the mass of test material used by the total volume of air passed through the chamber.
The nominal concentration is 401 % of the actual mean achieved atmosphere concentration and shows that keeping the aerosol airborne was moderately difficult.


PARTICLE SIZE DISTRIBUTION
The particle size of the generated atmosphere inside the exposure chamber was determined three times during the exposure period using a Marple Personal Cascade Impactor (Westech IS Ltd, Beds., UK). This device consisted of six impactor stages (8.6, 5.5, 3.8, 1.7, 0.86 and 0.41 µm cut points) with stainless steel collection substrates and a back up glass fibre filter, housed in an aluminium sampler. The sampler was temporarily sealed in a sampling port in the animals’ breathing zone and a suitable, known volume of exposure chamber air was drawn through it using a vacuum pump.
The collection substrates and backup filter were weighed before and after sampling and the weight of the test material, collected at each stage, calculated by the difference.
The mean amount for each stage was used to determine the cumulative amount below each cut-off point size. In this way, the proportion (%) of aerosol less than 8.6, 5.5, 3.8, 1.7, 0.86 and 0.41 µm was calculated.
The resulting values were converted to probits and plotted against Log10 cut-point size. From this plot, the Mass Median Aerodynamic Diameter (MMAD) was determined (as the 50 % point) and the geometric standard deviation was calculated. In addition the proportion (%) of aerosol less than 4 µm (considered to be the inhalable fraction) was determined.

The MMAD was 3.19 µm, resulting in an inhalable fraction (< 4 µm) of 62.0 %. The geometric standard deviation was 2.11.

Analytical verification of test atmosphere concentrations:

yes

Remarks:

The test atmosphere was sampled seventeen times during the exposure period and the actual concentration of the test material calculated.

Duration of exposure:

4 h

Concentrations:

5.09 mg/L

No. of animals per sex per dose:

3 animals per sex per dose

Control animals:

no

Details on study design:

- Duration of observation period following administration: all animals were observed for clinical signs at hourly intervals during exposure, immediately on removal from the restraining tubes at the end of exposure, one hour after termination of exposure and subsequently once daily for up to 14 days. Any evidence of overt toxicity was recorded at each observation.
- Frequency of observations and weighing: Individual bodyweights were recorded on arrival, prior to treatment on the day of exposure and on Days 1, 3, 7 and 14.
- Necropsy of survivors performed: yes. At the end of the 14 day observation period the animals were killed by intravenous overdose of sodium pentobarbitone. All animals were subjected to a full external and internal examination, and any macroscopic abnormalities were recorded. The respiratory tract was subjected to a detailed macroscopic examination for signs of irritancy or local toxicity.

Results and discussion

Effect levels

Sex:

male/female

Dose descriptor:

LC50

Effect level:

> 5.09 mg/L air (analytical)

Based on:

test mat.

Exp. duration:

4 h

Mortality:

There was no mortality during the study.

Clinical signs:

other: In addition to the observations considered to be due to the restraint procedure (such as hunched posture, pilo-erection and wet fur), increased respiratory rate was noted in all animals during exposure, on removal from the chamber and one hour post-exposu

Body weight:

All males and one female exhibited bodyweight losses or showed no bodyweight gain on the first day post-exposure. All male animals exhibited a reasonable bodyweight gain during the remainder of the observation period. In contrast, all female animals exhibited slight bodyweight losses from Days 1 to 3 post-exposure. Throughout the remainder of the observation period, all female animals then exhibited reasonable bodyweight gains.

Gross pathology:

No macroscopic findings were detected amongst animals at necropsy.

Any other information on results incl. tables

Table 1 Exposure Chamber Atmosphere Concentrations

Duration of Exposure (minutes)	Net Weight of Sample (mg)	Volume of Air Sampled (L)	Chamber Flow Rate (L/min)	Atmosphere Concentration (mg/L)
6	9.66	2	60	4.83
15	10.13	2	60	5.07
30	11.01	2	60	5.51
45	10.03	2	60	5.02
60	10.79	2	60	5.40
74	10.58	2	60	5.29
90	9.71	2	60	4.86
105	10.46	2	60	5.23
120	9.78	2	60	4.89
135	10.08	2	60	5.04
151	9.53	2	60	4.77
165	11.08	2	60	5.54
180	10.04	2	60	5.02
195	10.39	2	60	5.20
210	9.73	2	60	4.87
225	10.24	2	60	5.12
237	9.60	2	60	4.80

Mean achieved atmosphere concentration: 5.09 mg/L (standard deviation 0.24)

 

Nominal Concentration

-Test material used: 312 g

-Air flow: 60 L/min

-Total generation time: 255 minutes*

-Nominal concentration: 20.4 mg/L

 

*Test atmospheres were generated for a total of 15 minutes prior to animal insertion to ensure that the test material concentration was being achieved.

 

Table 2 Particle Size Distribution - Cascade Impactor Data

Impactor Stage Number	Cut Point (µm)	Amount Collected (mg) Per Sample Number			Mean Amount Collected (mg)
		1	2	3
3	8.6	0.17	0.13	0.11	0.14
4	5.5	0.86	0.43	0.33	0.54
5	3.8	0.95	0.51	0.48	0.65
6	1.7	1.08	0.53	0.58	0.73
7	0.86	0.56	0.28	0.29	0.38
8	0.41	0.19	0.03	0.08	0.10
Back-up filter	<0.41	0.01	0.00	0.01	0.01

Total mean amount of test material collected: 2.55 mg

 

Table 3 Particle Size Distribution - Calculation

Cut Point (µm)	Log10 Cut Point	Mean Cumulative Amount Less Than Cut Point
		(mg)	(%)	Probit
8.6	0.935	2.41	94.5	6.60
5.5	0.740	1.87	73.3	5.62
3.8	0.580	1.22	47.8	4.95
1.7	0.230	0.49	19.2	4.13
0.86	-0.066	0.11	4.31	3.29
0.41	-0.387	0.01	0.392	2.34

MMAD: 3.19 µm

Geometric standard deviation: 2.11

Predicted amount <4 µm: 62.0 %

Table 4 Individual Bodyweights

Animal Number and Sex	Bodyweight (g) on Day:						Increment (g) During Days:
	-8	0	1	3	7	14	-8 to 0	0 to 1	1 to 3	3 to 7	7 to 14
1 Male	238	277	273	278	298	313	39	-4	5	20	15
2 Male	242	272	270	271	285	301	30	-2	1	14	16
3 Male	234	273	266	271	283	298	39	-7	5	12	15
4 Female	204	227	229	225	231	239	23	2	-4	6	8
5 Female	192	211	212	208	210	221	19	1	-4	2	11
6 Female	192	215	215	212	219	225	23	0	-3	7	6

Applicant's summary and conclusion

Interpretation of results:

other: Not classified according to EU criteria.

Conclusions:

The 4 hour LC50 was determined to be >5.09 mg/L, therefore the test material requires no classification under the conditions of this study in accordance with EU criteria.

Executive summary:

The acute inhalation toxicity of the test material was determined in a study which was conducted in accordance with the standardised guideline OECD 436.

During the study male and female RccHan:WIST strain rats (3 per sex) were exposed (nose only) for 4 hours to a dust atmosphere containing the test material at a mean concentration of 5.09 mg/L, with a MMAD of 3.19 µm.

Following exposure, the animals were observed for 14 days for signs of mortality and toxicity. At the end of the observation period, all animals were subjected to necropsy.

No deaths and no clinical signs occurred throughout the study and the 4 hour LC50 was therefore determined to be > 5.09 mg/L. The test material requires no classification under the conditions of this study in accordance with EU criteria.