OSMIUM TETROXIDE

Osmium tetroxide
(Osmic acid, perosmic oxide, osmium(IV) oxide)
CAS 20816-12-0

OsO₄

Colorless to pale yellow-green crystals
bp 130 °C (but sublimes at lower temperature), mp 40 °C
Moderately soluble in water (7 g/100 mL)

Acrid, chlorine-like odor detectable at 2 ppm (20 mg/m³)

8.8 (air = 1.0)

7 mmHg at 20 °C

LD₅₀ oral (rat) 14 mg/kg

LC_LO inhal (rat) 40 ppm (4 h)

PEL (OSHA) 0.0002 ppm (0.002 mg/m³)

TLV-TWA (ACGIH) 0.0002 ppm (0.002 mg/m³)

STEL (ACGIH) 0.0006 ppm (0.006 mg/m³)

High acute toxicity; severe irritant of the eyes and respiratory tract; vapor can cause serious eye damage.

The acute toxicity of osmium tetroxide is high, and it is a severe irritant of the eyes and respiratory tract. Exposure to osmium tetroxide vapor can damage the cornea of the eye. Irritation is generally the initial symptom of exposure to low concentrations of osmium tetroxide vapor, and lacrimation, a gritty feeling in the eyes, and the appearance of rings around lights may also be noted. In most cases, recovery occurs in a few days. Concentrations of vapor that do not cause immediate irritation can have an insidious cumulative effect; symptoms may not be noted until several hours after exposure. Contact of the eyes with concentrated solutions of this substance can cause severe damage and possible blindness. Inhalation can cause headache, coughing, dizziness, lung damage, and difficult breathing and may be fatal. Contact of the vapor with skin can cause dermatitis, and direct contact with the solid can lead to severe irritation and burns. Exposure to osmium tetroxide via inhalation, skin contact, or ingestion can lead to systemic toxic effects involving liver and kidney damage. Osmium tetroxide is regarded as a substance with poor warning properties.

Chronic exposure to osmium tetroxide can result in an accumulation of osmium compounds in the liver and kidney and damage to these organs. Osmium tetroxide has been reported to cause reproductive toxicity in animals; this substance has not been shown to be carcinogenic or to show reproductive or developmental toxicity in humans.

Noncombustible

Osmium tetroxide reacts with hydrochloric acid to form chlorine gas.

Because of its high acute toxicity, osmium tetroxide should be handled in the laboratory using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with compounds of high toxicity (Chapter 5.D). In particular, all work with osmium tetroxide should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact. Osmium tetroxide as solid or solutions should be stored in tightly sealed containers, and these should be placed in secondary containers.

In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, promptly wash with copious amounts of water for 15 minutes (lifting upper and lower lids occasionally) and obtain medical attention. If osmium tetroxide is ingested, obtain medical attention immediately. If large amounts are inhaled, move the person to fresh air and seek medical attention at once.

In the event of a spill, mix osmium tetroxide with an absorbent material such as vermiculite or dry sand (avoid raising dust), place in an appropriate container, and dispose of properly. Evacuation and cleanup using respiratory protection may be necessary in the event of a large spill or release in a confined area.

Excess osmium tetroxide solutions can be rendered safer by reaction with sodium sulfite to produce insoluble osmium dioxide. Ethanol will also react to produce the dioxide. Corn oil or sodium sulfide may also be used to deactivate osmium tetroxide. Osmium-containing waste should be placed in a tightly sealed, labeled container and handled according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.