Dichloromethane (DCM), also known as methylene chloride, is a volatile, colourless liquid with a slightly sweet odour. Although it is not miscible with water, it readily mixes with most organic solvents. It does not occur naturally in the environment and is primarily manufactured for industrial use.
What is Dichloromethane used for?
DCM is widely used across several industries, mainly as a solvent due to its excellent ability to dissolve a variety of substances. Major applications include:
Paint strippers and removers
Pharmaceutical processing (drug manufacturing and film coating)
Electronics manufacturing (metal cleaning and finishing)
Urethane foam production (blowing agent)
Aerosol propellant in paints, insecticides, and automotive products
Additional specialised uses:
Food processing: extraction of spice oleoresins, hops, and formerly caffeine from coffee
Civil engineering: binder/aggregate separation in asphalt analysis
Plastic welding adhesive ("Di-clo") used in model-building and garment printing
Heat engine fluid: used in novelty items like bubble lights and displays due to its low boiling point
Dichloromethane (DCM) is used in pharmaceutical processing, including applications such as film coating.
Sources & Route of Exposure
Routes of exposure to dichloromethane are:
Inhalation: Primary route of exposure. Occurs during use of DCM-containing products (e.g., paint stripping). Indoor use may expose workers or consumers to higher levels.
Important hazard: When used near open flames, toxic phosgene gas may form.
Ingestion: May occur via contaminated water or food preparation.
Dermal: DCM can be absorbed through the skin, though this is typically a minor route.
Environmental presence:
Detected at hazardous waste sites, in surface and groundwater, and occasionally in drinking water at low concentrations.
Health Effects
Acute Effects
High-level inhalation can be fatal (e.g., during paint stripping in enclosed spaces)
Central nervous system (CNS) effects:
Dizziness, nausea, visual/auditory impairment, and impaired motor coordination
Tingling or numbness in extremities
Irritation: nose, throat, and skin
Skin exposure: cause burning, redness, and irritation
These effects are generally reversible once exposure stops.
Chronic Effects
CNS symptoms: persistent headaches, dizziness, memory loss
Organ toxicity: liver, kidneys, cardiovascular system (in animal studies)
EPA toxicity reference values:
RfC (inhalation): 3 mg/m³ (based on rat liver effects)
RfD (oral): 0.06 mg/kg/day (based on rat liver toxicity)
Reproductive & Developmental Effects
Human data: No definitive studies on reproductive or developmental harm
Animal studies:
DCM crosses the placental barrier
Observed effects: reduced foetal body weight and minor skeletal variations
Cancer Risk
Epidemiological studies: No conclusive evidence of increased cancer risk in exposed human workers
Animal studies:
Increased incidence of liver and lung tumours
Benign mammary gland tumours observed in rodents
The U.S. EPA classifies dichloromethane as a Group B2—probable human carcinogen.
Safety
First Aid Measures
Eye Contact: Immediately flush eyes with copious amounts of water for at least 15 minutes. Seek medical attention promptly.
Skin Contact: Rinse affected skin thoroughly with water. Remove any contaminated clothing or footwear. If irritation develops or persists, obtain medical attention. Launder clothing before reuse.
Ingestion: Do not induce vomiting unless directed by medical personnel. Never administer anything orally to an unconscious individual. Promptly seek medical attention.
Inhalation: Remove the exposed person to fresh air immediately. If breathing has stopped, begin artificial respiration. Administer oxygen if breathing is difficult. Seek medical help without delay.
Exposure Controls & Personal Protection
Engineering Controls
Workplaces handling dichloromethane should be equipped with:
Eyewash stations
Safety showers
Ensure adequate ventilation, such as local exhaust systems, to maintain airborne concentrations below occupational exposure limits.
Personal Protective Equipment
Eyes: Use chemical safety goggles to protect against splashes.
Safe Work Australia has set an allowable limit for workers to be exposed to 50 parts per million dichloromethane over an eight-hour workshift. It has determined that dichloromethane is a Category 3, suspected carcinogen. It is possible that there is no safe level of exposure to a carcinogen.
Australian Drinking Water Quality Guidelines (NHMRC and ARMCANZ, 1996): 0.004 mg/L (i.e. 0.000004 g/L).
Europe
Dichloromethane use is regulated under the Solvent Emissions Directive (1999/13/EC).
Dichloromethane will be controlled under the EU Water Framework Directive (2000/60 EC).
Environmental exposure
Air: The atmospheric lifetime of dichloromethane is several months. Due to its high volatility, this substance will mainly be transferred from the aquatic environment to air. In the troposphere, methylene chloride is then broken down in carbon dioxide and hydrogen chloride.
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