Chloroform, or trichloromethane (\(\text{CHCl}_3\)), is a heavy, clear, volatile liquid known for its characteristic sweet, almost minty odor. This organochloride compound is structurally composed of a single carbon atom bonded to one hydrogen atom and three chlorine atoms. Its high volatility means it readily evaporates into a gas upon exposure to air, making inhalation the primary route of exposure.
From Operating Room to Obsolete: Chloroform’s Medical History
The history of chloroform in medicine began in 1847 when Scottish physician James Young Simpson first used it as a general anesthetic. Its introduction led to rapid adoption in operating rooms, primarily because it was non-flammable, unlike the highly combustible ether then in use for surgery. The chemical’s effectiveness in quickly inducing unconsciousness made it a preferred choice for physicians, including John Snow, who famously administered it to Queen Victoria during the birth of her last two children in the 1850s.
However, the enthusiasm for chloroform soon faded as reports of patient deaths during anesthesia began to accumulate. Early statistics revealed a significant difference in fatal complications, with chloroform carrying a risk estimated to be between 1 in 3,000 and 1 in 6,000 administrations, a much higher rate than ether. The medical community gradually realized the fine line between an anesthetic dose and a fatal overdose was dangerously thin.
Concerns over these high mortality rates led to the chemical’s gradual abandonment in the early 20th century. The rise of safer, more controllable gaseous anesthetics and improved administration equipment further hastened its decline. Despite a brief, failed attempt to reintroduce it in the 1940s, the use of chloroform in the Western world’s operating rooms was largely discontinued by the 1970s.
How Chloroform Affects the Human Body
When inhaled, chloroform acts as a powerful central nervous system (CNS) depressant. Symptoms progress from inebriation and excitation to narcosis and then deep unconsciousness. The chemical functions by modulating receptors in the brain, notably acting as a positive allosteric modulator at \(\text{GABA}_\text{A}\) receptors, which inhibits nerve cell activity. This widespread suppression causes the anesthetic effect but also rapidly depresses the brain’s control centers for breathing and circulation.
The primary danger of being “chloroformed” is the risk of fatal cardiac arrhythmia. Chloroform sensitizes the heart muscle to the effects of adrenaline and similar compounds, causing the heart rhythm to destabilize and stop abruptly. Even a short exposure to high concentrations can cause this cardiac sensitization, making the chemical lethal before respiratory depression fully sets in.
Beyond the acute risk, the body’s attempt to metabolize chloroform creates highly toxic breakdown products, which cause severe, delayed organ damage. The liver is the primary site of metabolism, where enzymes convert the compound into a reactive intermediate that causes hepatotoxicity. This liver damage, which can lead to jaundice and coma, may not become apparent until 24 to 48 hours after exposure. The kidneys are also targets for this toxicity, resulting in nephrotoxicity and potential renal failure.
Where Chloroform Exists Today
While its medical application is a relic of the past, chloroform remains an important industrial and laboratory chemical. Most of the chloroform produced today is utilized as a chemical intermediate, especially in the manufacturing of refrigerants like HCFC-22 and the production of polytetrafluoroethylene (PTFE). It is also widely used as a solvent in various industries due to its ability to dissolve a wide range of organic compounds.
The most common source of contemporary public exposure to chloroform is through its formation as a disinfection byproduct (DBP). This occurs when chlorine, used to disinfect water, reacts with naturally occurring organic matter present in the raw water supply. Consequently, trace amounts of chloroform are often present in municipal drinking water, wastewater, and chlorinated swimming pools.
The presence of chloroform in the environment, even at low levels, is why it is regulated by environmental protection agencies. Exposure can still occur in workplaces that manufacture or use it as a solvent or precursor. The chemical’s classification as a probable human carcinogen requires its continued monitoring in both industrial settings and public water supplies.