Methyl Isocyanate Toxicity: A Detailed Analysis

What Is Methyl Isocyanate?

Methyl isocyanate is a highly flammable liquid that easily evaporates when exposed to air at temperatures below 39º centigrade (102º Fahrenheit). Methyl isocyanate is about 1.4 times heavier than air in gas form. Liquid methyl isocyanate is colorless and smells strong. Most persons can detect the fumes of methyl isocyanate at concentrations as low as 2 to 5 ppm. The liquid methyl isocyanate is managed and transported as an explosive and highly flammable substance.

How Is Methyl Isocyanate Exposed?

• Inhalation: The main method of exposure to methyl isocyanate is inhalation. The fumes are quickly taken in by the lungs. The respiratory and ocular epithelium may become irritated after exposure to methyl isocyanate fumes acutely below the odor threshold. Acute exposure to greater vapor concentrations can result in fatal lung damage, severe pulmonary edema, and damage to the lung's alveolar walls. Acute exposure survivors may experience long-term respiratory consequences. Humans may smell methyl isocyanate fumes at levels between two and five ppm (parts per million). Accidental releases of methyl isocyanate into the air, like the one in Bhopal, India, in 1984. The main consequence was pulmonary edema with some alveolar wall loss, most likely resulting in significant exposure to methyl isocyanate vapors. As methyl isocyanate is heavier than air, exposure in cramped spaces or low-lying regions may cause asphyxiation (suffocation).

• Eye or Skin Contact: Direct contact with methyl isocyanate liquid or intense fumes can harm the eyes and cause serious skin and eye irritation. Dermal absorption may occur when direct skin contact occurs. Outside of a workplace where methyl isocyanate is kept or utilized, significant cutaneous exposure to the chemical is unlikely to occur. Children are more susceptible to toxicants absorbed via the skin because of their considerably greater surface area: weight ratio.

• Ingestion: Consuming liquid methyl isocyanate might cause significant gastrointestinal upset, although this is uncommon.

What Are the Uses of Methyl Isocyanate?

The uses of methyl isocyanate include

• Methylamine and phosgene are combined to create methyl isocyanate. Methyl isocyanate is primarily used as a chemical intermediary in the synthesis of insecticides. Plastics and polyurethane foams are also made using it.

What Are the Harmful Effects Caused Due to Methyl Isocyanate Toxicity?

Methyl isocyanate's harmful mechanisms are not fully understood. However, blood proteins, including globin, may be affected by carbamylation. Given that antibodies specific to methyl isocyanate have been found in the blood of patients exposed to it, persistent respiratory and ocular effects may reflect immunologic effects caused by methyl isocyanate. Due to its high level of reactivity, methyl isocyanate is not digested in the traditional sense. In rare instances, the consequences of acute exposure to methyl isocyanate on the respiratory system might start occurring right away. In others, respiratory damage might progress over periods of hours or days. When pneumonia develops, exposure-related mortality can occasionally happen 30 or more days after the initial exposure.

Acute Exposure:

• Respiratory: The respiratory system is highly irritated and corroded by the fumes of methyl isocyanate. Cough, chest discomfort, dyspnea (shortness of breath), coma, and death are possible symptoms. Instinctive reactions to exposure may include irritating respiratory symptoms like pulmonary edema and bronchial spasms. The consequences of pneumonia and alveolar wall deterioration that might result from methyl isocyanate-induced pulmonary edema can eventually cause respiratory failure and mortality.

• Ocular or Ophthalmic: Direct contact with the liquid or exposure to its fumes can cause severe eye irritation. Immediate eye discomfort, lacrimation, photophobia (sensitivity to light), severe lid edema, and corneal ulcerations are possible symptoms. Ocular exposure can permanently harm the eyes over a lengthy period.

• Skin: When methyl isocyanate comes into contact with the skin, it irritates the skin and, at high exposure levels, can result in chemical burns. Children are particularly susceptible to skin toxins because their body weight to surface area ratio is significantly greater.

• Gastrointestinal: Acute exposure to methyl isocyanate vapors has been associated with nausea, vomiting, stomach discomfort, and defecation.

Chronic Exposure

• Respiratory: Chronic obstructive pulmonary disease may be brought on by prolonged exposure to methyl isocyanate.

• Impact on Reproduction and Development and Carcinogenicity: The carcinogenicity of methyl isocyanate has not been determined.

Methyl isocyanate is not among the 30 compounds on the list of reproductive and developmental toxicants, which was included in a 1991 study by the U.S. General Accounting Office and contained substances of concern due to well-known effects on reproduction and development. For months after exposure, higher incidence of spontaneous abortions and infant mortality were seen among Bhopal tragedy victims. However, it is challenging to pinpoint exactly how methyl isocyanate contributes to developmental damage.

How to Manage the Toxicity of Methyl Isocyanate?

Start ABC (Airway, Breathing, Circulation): Immediately create a patent airway. Maintain cervical immobilization manually if trauma is suspected, and where practical, attach a cervical collar and a backboard. Assure proper breathing and heartbeat. Establish intravenous access if required and give more oxygen as needed; if one is accessible, place it on a heart monitor.

Decontamination: Keep rinsing the eyes and any exposed skin as necessary. Avoid causing emesis when there has been intake. Instead, consider giving charcoal at a dose of 1 g/kg (gram per kilogram) in infant, child, and adult if the person is not exhibiting any symptoms.

Advanced Treatment:

• Use procedures and techniques that are both readily available and within the bounds of training to treat cases of respiratory compromise with respiratory support. In some circumstances, suitably educated and equipped professionals may be required to perform operations like endotracheal intubation or cricothyrotomy.

• According to established protocol, oxygen therapy for bronchospasm, aerosolized bronchodilators such as Albuterol, and steroids are necessary for treating patients.

• Noncardiogenic pulmonary edema can have a delayed start and nevertheless maintain proper oxygenation and ventilation. It could be necessary to start using mechanical breathing and positive end-expiratory pressure (PEEP) right away. Use the least amount of PEEP necessary while retaining sufficient oxygenation to reduce trauma and other problems. Take into account medication for pulmonary edema.

• Advanced life support (ALS) guidelines should be followed while treating patients with seizures or cardiac arrhythmias and hypotension.

• Start administering fluids if shock or hypotension is detected. Those with systolic pressure less than 80 mm Hg may benefit from a 1,000 mL/hour (milliliter per hour) bolus perfusion of intravenous saline or lactated Ringer's solution. Lower perfusion rates may be necessary due to higher adult systolic pressures. Provide a 20 mL/kg normal saline bolus to children with poor perfusion over 10 to 20 minutes, and then infuse at a rate of 2 to 3 mL/kg/hour. Consider vasopressors if the patient is hypotensive and has a normal fluid volume.

Conclusion

The respiratory system and eyes are badly irritated and corroded by the fumes of methyl isocyanate. Methyl isocyanate side effects can be treated, although no known antidote exists. Patients who have breathed significant levels of methyl isocyanate will probably need to be hospitalized. The person must notify the employer, the National Institute for Occupational Safety and Health, or the Occupational Safety and Health Administration (OSHA), if there is exposure at work.