Boron

Acute Toxicity: inhalation

Administrative data

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2001-02-21 to 2001-03-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study reliable without restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2001

Report date:

2001

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2001-01-15

Test type:

standard acute method

Limit test:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Boron

EC Number:

231-151-2

EC Name:

Boron

Cas Number:

7440-42-8

Molecular formula:

B

IUPAC Name:

borane

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Details on test material:

- Name of test material (as cited in study report): Boron amorphous
- Physical state: a brown powder
- Storage condition of test material: in the dark at ambient room temperature (approx. 20°C) and in the original container.
- Average particle size: 0.9 µm
- Specific surface area: 11.1 m^2/g

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River UK Limited, Manston Road, Margate, Kent, England
- Age at study initiation: males: approximately 8 weeks; females: approximately 9 weeks
- Weight at study initiation: males: 254 - 302 g; females: 193 - 234 g
- Housing: the animals were housed by sex, in groups of 5. The holding cages were made of stainless steel sheet and wire mesh and were suspended on a movable rack. Plastic trays, lined with absorbent paper, were placed below each cage to collect animal excreta.
- Diet (ad libitum): SDS rat and mouse diet (RM1 (E) SQC expanded pellet)
- Water (ad libitum): tap water (supplied by Anglian Water)
- Acclimation period: 5 days before the day of exposure

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 3°C (maximum: 20.5°C; minimum: 20.0°C)
- Relative humidity: 50% ± 20% (maximum: 65%; minimum: 36%)
- Air changes: at least 15 air changes per hour
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

air

Details on inhalation exposure:

NOTE: A group, allocated to an associated study conducted for the sponsor (Study number SKC/041) acted as a common control and received clean air only for 4 hours.

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus/ Exposure chamber volume / Method of holding animals in test chamber: the snout-only exposure chambers (ADG Developments Ltd., Hitchin, Hertfordshire, England) used for the exposures were of cylindrical form (30 cm diameter, 45 cm height) and made of aluminium alloy. The internal surfaces of the chamber have a conformal chemically resistant coating. The chambers have an enclosed volume of approximately 30 litres. The animals were held for exposure in moulded polycarbonate restraining tubes, which were attached at evenly spaced ports in the cylindrical section of the chamber, and were designed to allow only the snout to project into the chamber. Each animal was restrained in a forward position by an adjustable foamed plastic stopper, which also provided a seal for the tube.
The exposure chamber was 'earthed' using a copper wire in order to reduce any electrostatic charge present.
The exposure system was positioned inside a large cabinet equipped with an extract fan exhausting to atmosphere through an absolute filter.
Each animal was placed into a separate restraining tube and the tubes were then attached to the exposure chamber.

- System of generating particulates/aerosols: a Wright Dust Feed mechanism (WRIGHT, B.M. (1950))* was used to produce the test atmosphere containing a particulate aerosol generated from boron amorphous.
The WDF was designed to produce and maintain atmosphere containing a particulate aerosol by suspending material scraped from the surface of a compressed powder in a stream of dry air. The concentration of particulate aerosol in the air is determined by the rate at which the scraper blade is advanced into the compressed powder.
A jet was fitted to the WDF to break-up aggregates emitted from the aerosol generator.
The WDF was 'earthed' using a copper wire in order to reduce any electrostatic charge present.
The test atmosphere was passed through a vertical glass elutriator to reduce, by sedimentation, the amount of non-respirable particulate in the test atmosphere. The elutriator was 'earthed' using a copper wire and 'neutralised' air was passed externally over the elutriator to remove any electrostatic charge and hence optimise aerosol generation.

The conditioned test atmosphere entered through a port at the top centre of the chamber and passed out through a port at the base section below the level of the animals.

A sample of the test substance was packed into the container of the Wright Dust Feed mechanism (WDF) using a hydraulic bench press to assist packing. An even density of the test substance was achieved by packing the container in stages and applying a force of 2.0 ton to compress the powder. The applied force was sufficient to prevent disintegration of the packed powder during the generation procedure. The packed container was weighed.
A supply of clean, dry air was connected to the generator and the supply pressure was adjusted to give a flow rate of 15 litres/minute, measured at the generator outlet. A continuous stream of 'neutralised' air was directed over and along the exterior of the elutriator to aid the removal of any electrostatic charge. In-line flow meters were used to monitor the generator air supply and exhaust airflow throughout the exposure. The exhaust airflow was calibrated and adjusted to produce a slightly negative pressure.
The WDF was positioned vertically on a stand at the side of the exposure chamber and the output was connected to the top inlet port of the chamber via the elutriation column. An initial speed controller setting of '37% of the maximum speed' of the WDF was selected, as a result of preliminary generation trials, to generate a concentration of total particulate at the target concentration of 5 mg/L. The WDF speed setting was adjusted as necessary during the exposure in order to ensure generation of the test aerosol close to target.

The powder container of the WDF was advanced manually until a trace of suspended dust was seen to emerge from the WDF outlet. The gearing on the generator was then engaged and the generator motor switched on to start the exposure.
After the equilibration period of 5 minutes, the exposure was timed for 4 hours. The WDFD canister was replaced with a further packed canister as required during the exposure. The generator was then switched off and the chamber was allowed to clear before the animals were removed for examination.
Following exposure, the animals were returned to the holding cages where food and water were available. The test animals were kept in a ventilated cabinet overnight and then returned to the holding room for the remainder of the observation period.
The control group was treated similarly but received clean air only for 4-hours. The control animals were returned to the holding room at the end of the exposure period.

- Method of particle size determination: two air samples were taken during the exposure at a sampling rate of 2 litres/minute using a Marple cascade impactor (Model 298, Graseby Andersen inc., Atlanta, Georgia, USA) to determine particle size distribution. The samples were taken at 87 and 204 minutes into exposure. The volume of air sampled was measured using a wet-type gas meter (Model DM3B, G.H. Zeal Ltd., London, England (formally Alexander Wright and Co., Sutton, Surrey, England)).
The amount of material collected on the stages of the sampler was determined gravimetrically. The particle size distribution of the test atmosphere was assessed using linear regression analysis. The probit of the cumulative percentage of the total particles collected, smaller than the cut-point of each stage, was plotted against the logarithm of the cut-point of each stage.

- Temperature and relative: the air temperature in the exposure chamber was measured using an alcohol-in-glass thermometer and the relative humidity was determined using an Analytical Development Company Ltd., infra red water vapour analyser. The temperature and relative humidity were determined at the start of exposure and then at 30-minute intervals during the 4-hour exposure (Temperature (mean): 19.4± 0.22 °C (control group) and 19.9 ± 0.22°C (test group)) (Relative humidity (mean): 29% ± 3.7 (control group) and 36% ± 3.3 (test group)).

TEST ATMOSPHERE
- Brief description of analytical method used: six samples of air were removed from the test chamber during exposure in order to determine the concentration of the test aerosol. In the first instance, samples were obtained following equilibration and generally at approximately hourly intervals thereafter. An additional sample was obtained as necessary to monitor the chamber concentration following an adjustment to the exposure system in order to ensure satisfactory generation.
Each air sample was withdrawn, at a rate of 2 litres/minute, through a pre-weighed glass fibre filter (Schleicher & Schuell GF/50 filters) mounted in an open face filter holder. The volume of air sampled was measured using a wet-type gas meter (Model DM3B, G.H. Zeal Ltd., London, England (formally Alexander Wright and Co., Sutton, Surrey, England)). The filters were re-weighed following sampling for gravimetric analysis of the test aerosol.
- Nominal concentration: the nominal concentration of the test substance in the exposure chamber was calculated from the total mass of boron amorphous dispersed by the dust generator and the total volume of air flowing through the exposure system during the period of generation.

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution: approximately 91% of the particulate were considered of a respirable size (< 7 µm in aerodynamic diameter)
- MMAD: 2.4 µm (GSD: 2.15)

* Reference:
- WRIGHT, B.M. (1950) A new dust-feed mechanism, J.Sc. Instr. 27: 12

Analytical verification of test atmosphere concentrations:

yes

Remarks:

please refer to "Details on inhalation exposure" and "Any other information on materials and methods incl. tables" above and below, respectively.

Duration of exposure:

4 h

Concentrations:

Actual concentration:
5.08 mg/L ± 0.250
Nominal concentration. 13.8 mg/L

No. of animals per sex per dose:

5 males / 5 females

Control animals:

yes

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: throughout the study, all cages were checked at least twice daily, once in the morning and again towards the end of the normal working day, for dead or moribund animals. The animals were observed intermittently for signs of reaction to the test substance during exposure and at least twice daily throughout the observation period. The clinical signs were recorded at the end of the chamber equilibrium period, at 0.25, 0.5 and 1.0 hour then at hourly intervals during the exposure. Clinical signs were recorded immediately following exposure and then at 1.0 and 2.0 hours post-exposure. During the observation period, the clinical signs were recorded once in the morning and then as necessary following a later check for survival.
All the animals were weighed at least twice during the week prior to exposure, prior to exposure (Day 0), weekly during the observation period and on the day of death.
A visual inspection of water bottles was conducted daily.
- Necropsy of survivors performed: yes
All animals were subjected to a detailed macroscopic examination. The lungs (including the larynx and trachea) were removed, dissected clear of surrounding tissue, weighed and the weights recorded.

Statistics:

not applicable

Results and discussion

Effect levels

Sex:

male/female

Dose descriptor:

LC50

Effect level:

> 5.08 mg/L air (analytical)

Based on:

test mat.

Exp. duration:

4 h

Mortality:

There were no unscheduled deaths.

Clinical signs:

other: During exposure: Exaggerated breathing was evident in most test rats from 15 minutes, and all test rats from 30 minutes into exposure. Brown staining of fur on head was observed for all test rats from 1 hour into exposure. Soiling of the fur with excreta

Body weight:

There were no treatment-related effects.

Gross pathology:

A brown discolouration was evident on the lungs of all test rats. Congestion was also noted on the lungs of the majority of test rats. Small dark foci were noted on the lungs of a control rat and two test rats.
Dark discolouration, small dark foci or severe congestion were noted on the thymus for a proportion of test rats. Small pale areas were noted on the right kidney of two female test rats.
The external finding of brown staining on the tail was noted for all test rats prior to necropsy.

Other findings:

- Water consumption: there were no treatment-related effects.
- Lung weights: the lung weights of test rats were higher than control values and is consistent with the macroscopic findings noted above.

Applicant's summary and conclusion

Interpretation of results:

not classified

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

LC50 (male and female rats, 4 hours) > 5.08 mg/L air (analytical)
According to the EC-Commission directive 67/548/EEC and its subsequent amendments, the test substance is not classified as acute toxic via the inhalation route.
According to the EC-Regulation 1272/2008 and subsequent regulations, the test item is not classified as acute toxic via the inhalation route.