CHROMIUM TRIOXID
AND OTHER CHROMIUM(VI) SALTS

Chromium trioxide
(Chromic anhydride; chromic acid; chromium(VI) oxide; chromic trioxide; chromium oxide)
CAS 1333-82-0

CrO₃

Dark red flakes or crystals
mp 196 °C, bp: decomposes at 250 °C
Very soluble in water (62 g/100 mL)

Noncombustible

LD₅₀ oral (rat) 80 mg/kg

PEL (OSHA) 0.1 mg (CrO₃)/m³(ceiling)

TLV-TWA (ACGIH) 0.05 mg (Cr)/m ³

Probable human carcinogen (OSHA "select carcinogen"); severely irritating to the skin and mucous membranes; very strong oxidizing agent.

Chromium trioxide and other chromium(VI) salts are moderately toxic substances by ingestion; 1 to 15 g may be a fatal dose in humans. Ingestion of nonlethal doses of these compounds can cause stomach, liver, and kidney damage; symptoms may include clammy, cyanotic skin, sore throat, gastric burning, vomiting, and diarrhea. Chromic acid is irritating to the skin, and prolonged contact can cause ulceration. Inhalation of chromate dust or chromic acid mist can result in severe irritation of the nose, throat, bronchial tubes, and lungs and may cause coughing, labored breathing, and swelling of the larynx. Eye contact with chromium trioxide and its solutions can cause severe burns and possible loss of vision.

Occupational exposure to chromium(VI) compounds has been related to an increased risk of lung cancer. Several hexavalent compounds of chromium, including chromium trioxide, are listed in IARC Group 1 ("carcinogenic to humans") and are classified as "select carcinogens" under the criteria of the OSHA Laboratory Standard. Long-term exposure to chromium trioxide or chromium(VI) salts may cause ulceration of the respiratory system and skin. Exposure to chromium trioxide by inhalation or skin contact may lead to sensitization. Chromium trioxide has exhibited teratogenic activity in animal tests.

Chromium trioxide is not combustible but is a strong oxidizing agent and can accelerate the burning rate of combustible materials. Contact with easily oxidized organic or other combustible materials (including paper and oil) may result in ignition, violent combustion, or explosion. The use of dry chemical, carbon dioxide, Halon, or water spray extinguishers is recommended for fires involving chromium(VI) compounds.

Chromium trioxide and certain other chromium(VI) compounds are useful as strong oxidizing agents in the laboratory, but appropriate precautionary measures should be taken when conducting these reactions. Chromium trioxide has been reported to react violently with a variety of substances, including readily oxidized organic compounds such as acetone, acetaldehyde, methanol, ethanol, diethyl ether, ethyl acetate, acetic acid, and DMF, and violent reactions may also occur on reaction with alkali metals, gaseous ammonia, phosphorus, and selenium.

Because of their carcinogenicity, chromium(VI) compounds should be handled 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, chromium trioxide should be handled in a fume hood to avoid the inhalation of dust, and impermeable gloves should be worn at all times to prevent skin contact. The practice of using chromate solutions to clean glassware should be avoided. Chromium trioxide should be stored in areas separated from readily oxidized materials.

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 min (lifting upper and lower lids occasionally) and obtain medical attention. If chromium trioxide or other chromium compounds are ingested, give the person large amounts of water or milk and obtain medical attention immediately. If dust or aerosols of these compounds are inhaled, move the person to fresh air and seek medical attention at once.

In the event of a spill, remove all combustibles from the area, sweep up the chromium compounds, place in an appropriate container, and dispose of properly. In the event solutions containing chromium compounds are spilled, neutralize (if possible) with aqueous base, soak up with a spill pillow or appropriate noncombustible absorbent material, place in an appropriate container, and dispose of properly. Respiratory protection may be necessary in the event of a large spill of powder, particularly in a confined area.

Excess chromium compounds and waste material containing these substances should be placed in an appropriate container, clearly labeled, 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.