Methyl Isocyanate

Abstract

Methyl isocyanate (MIC) is a bitter reminder of the Bhopal disaster in 1984. Bhopal is the capital of the central province Madhya Pradesh, India (estimated population in 1984 was slightly less than 1 million). MIC is extremely toxic to humans from acute (short-term) exposure. It is a colorless liquid with a sharp pungent odor. MIC is prepared industrially by reacting methylamine with phosgene, oxidizing monomethylformamide at high temperatures (>550 °C), or heating metal MICs. MIC is also manufactured from N-methylformamide and air. Because of its high reactivity, MIC is used as an intermediate in organic synthesis, most notably in the production of carbamate-based pesticides. Tobacco smoke from some brands of cigarettes also contains MIC, approximately 4 μg per cigarette. Most of our knowledge on the toxic effects of MIC on humans is derived from the Union Carbide's battery manufacturing plant explosion accident in Bhopal in 1984. Within days of the initial exposure to MIC, thousands died, and additional deaths occurred during the following years. Exposure to MIC contaminated air can cause extreme irritation and difficulty in breathing. Temporary reversible blindness may occur depending on the length of exposure. MIC exposure can lead to development of pulmonary edema, bronchospasm, or electrolyte imbalance. Adverse health effects of MIC can continue for decades in populations exposed to MIC. MIC exposed humans may exhibit lung, ocular, and reproductive effects for years; stillbirths and spontaneous abortions are also very common. EPA has classified methyl isocyanate as a Group D, not classifiable as to human carcinogenicity.