Is Chloroform safe when breathed in?

Chloroform is classified as a probable human carcinogen by regulatory bodies, including the U.S. Environmental Protection Agency (EPA Group B2), the International Agency for Research on Cancer (IARC Group 2B: possibly carcinogenic to humans), and the U.S. Department of Health and Human Services' National Toxicology Program (NTP: reasonably anticipated to be a human carcinogen).

Why here

This classification applies to all routes of exposure, including inhalation, with animal studies demonstrating kidney and liver tumors following inhalation exposure.

What would have to be true

Long-term inhalation exposure, particularly at high dose levels that lead to cell damage and subsequent regenerative cell proliferation.

Acute inhalation of chloroform vapors can cause irritation of the nose and throat, as well as central nervous system depression leading to symptoms such as headaches, dizziness, nausea, disorientation, fatigue, and at higher concentrations, unconsciousness, cardiac arrhythmias, convulsions, coma, and death.

Why here

These are direct and immediate effects observed in humans and animals upon inhaling chloroform.

What would have to be true

Short-term inhalation exposure to low-to-moderate levels (e.g., 920 ppm for 3 minutes for dizziness/vertigo, 1400 ppm for 30 minutes for lightheadedness/headache) to high concentrations (e.g., >13,000 ppm for cardiac arrhythmias, 40,000 ppm for several minutes may be lethal).

Chronic inhalation exposure to chloroform can lead to significant organ damage, particularly to the liver (e.g., hepatitis, jaundice, necrosis) and kidneys (e.g., renal tubular necrosis, renal dysfunction), and can also affect the central nervous system (e.g., headaches, dizziness, confusion, impaired concentration, memory problems, irritability, depression). This toxicity is largely attributed to the metabolic activation of chloroform in the liver, which produces reactive intermediates like phosgene.

Why here

Chloroform is readily absorbed through the lungs and metabolized in the body, with its toxic metabolites causing systemic effects on vital organs.

What would have to be true

Long-term/chronic inhalation exposure.

Inhalation exposure to chloroform has been linked in animal studies to adverse pregnancy outcomes, including increased incidence of resorption and decreased number of live fetuses, generally occurring at doses associated with maternal toxicity.

Why here

Animal studies specifically investigated the effects of chloroform inhalation during gestation on reproductive and developmental endpoints.

What would have to be true

High inhalation exposure concentrations (e.g., ≥291 ppm for 7 hours/day for 10 days in rats).

Ingesting drinking water containing chloroform, a disinfection byproduct, is associated with an increased risk of liver, kidney, and bladder cancers, and can cause damage to the liver, kidneys, and central nervous system.

Why here

Chloroform is a disinfection byproduct (DBP) formed when chlorine, used to treat drinking water, reacts with naturally occurring organic materials.

What would have to be true

Exposure occurs through drinking water, with the US EPA setting a Maximum Contaminant Level (MCL) for total trihalomethanes (including chloroform) at 80 parts per billion (ppb) (0.080 mg/L). The EPA's non-enforceable Maximum Contaminant Level Goal (MCLG) for chloroform is 70 ppb (0.07 mg/L), while the World Health Organization (WHO) guideline value is 0.3 mg/L (300 ppb). The Environmental Working Group (EWG) suggests a health guideline of 0.4 ppb to protect against cancer risk.