Dichloromethane

Dichloromethane (DCM) — or methylene chloride — is an organic compound with the formula CH2Cl2. This colourless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents. Dichloromethane does not occur naturally in the environment. [fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][1,2]

 

Uses [3]

 

Dichloromethane is predominantly used as a solvent in paint strippers and removers; as a process solvent in the manufacture of drugs, pharmaceuticals, and film coatings; as a metal cleaning and finishing solvent in electronics manufacturing; and as an agent in urethane foam blowing. In addition, it is used as a propellant in aerosols for products such as paints, automotive products, and insect sprays. Dichloromethane is used as an extraction solvent for spice oleoresins, hops, and for the removal of caffeine from coffee. However, due to concern over residual solvent, most decaffeinators no longer use it. Dichloromethane is also approved for use as a post harvest fumigant for grains and strawberries and as a degreening agent for citrus fruit. Dichloromethane’s low boiling point allows the chemical to function as a heat engine that can extract movement from low-grade temperatures. It can also be used to weld certain plastics. Often sold as a main component of plastic welding adhesives, it is also used extensively by model building hobbyists for joining plastic components together — it is commonly referred to as “Di-clo.” Dichloromethane is also used in the garment printing industry for removal of heat-sealed garment transfers, and its volatility is exploited in novelty items — bubble lights and jukebox displays. Furthermore, it is used in the material testing field of civil engineering; specifically it is used during the testing of bituminous materials as a solvent to separate the binder from the aggregate of an asphalt or macadam to allow the testing of the materials.

 

Sources & Routes of Exposure [2,4]

 

Routes of exposure to dichloromethane are:

  • Inhalation: Most cases of human exposure to dichloromethane occur when people breathe vapours from paint strippers. When household water becomes contaminated, people can inhale vapours while showering, laundering, and cooking. When dichloromethane is used near an open flame, poisonous “phosgene” gas can be created. Phosgene can cause permanent lung damage at low levels.
  • Ingestion: People can be exposed when they drink contaminated water or when they use it for preparing food.
  • Dermal: Dichloromethane can be absorbed through the skin, but this is a minor route of exposure.

The principal route of human exposure to dichloromethane is inhalation of ambient air. Occupational and consumer exposure to dichloromethane in indoor air may be much higher, especially from spray painting or other aerosol uses. People who work in these places can breathe in the chemical or it may come in contact with the skin. Dichloromethane has been detected in both surface water and groundwater samples taken at hazardous waste sites and in drinking water at very low concentrations.

 

Health Effects [2,3]

 

Acute Effects

 

Case studies of dichloromethane poisoning during paint stripping operations have demonstrated that inhalation exposure to extremely high levels can be fatal to humans. Acute inhalation exposure to high levels of dichloromethane in humans has resulted in effects on the central nervous system (CNS) including decreased visual, auditory, and psychomotor functions, but these effects are reversible once exposure ceases. In addition, dichloromethane irritates the nose and throat at high concentrations. People exposed to dichloromethane may feel unsteady, dizzy, and have nausea and a tingling or numbness of your finger and toes. A person breathing smaller amounts of methylene chloride may become less attentive and less accurate in tasks requiring hand-eye coordination. Skin contact with methylene chloride causes burning and redness of the skin.

 

Chronic Effects

The major effects from chronic inhalation exposure to methylene chloride in humans are effects on the CNS, such as headaches, dizziness, nausea, and memory loss. Animal studies indicate that the inhalation of methylene chloride causes effects on the liver, kidney, CNS, and cardiovascular system. EPA has calculated a provisional Reference Concentration (RfC) of 3 milligrams per cubic meter (mg/m3) based on liver effects in rats. The Reference Dose (RfD) for dichloromethane is 0.06 milligrams per kilogram body weight per day (mg/kg/d) based on liver toxicity in rats.

 

Reproductive/Developmental Effects

 

No studies were found regarding developmental or reproductive effects in humans from inhalation or oral exposure. However, animal studies have demonstrated that dichloromethane crosses the placental barrier, and minor skeletal variations and lowered foetal body weights have been noted.

 

Cancer Risk

 

Several studies did not report a statistically significant increase in deaths from cancer among workers exposed to methylene chloride. Animal studies have shown an increase in liver and lung cancer and benign mammary gland tumours following inhalation exposure to dichloromethane. EPA considers dichloromethane to be a probable human carcinogen and has ranked it in EPA’s Group B2.

 

Safety [5]

 

First Aid Measures

 

  • Eyes: In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. Get medical aid.
  • Skin: In case of contact, flush skin with plenty of water. Remove contaminated clothing and shoes. Get medical aid if irritation develops and persists. Wash clothing before reuse.
  • Ingestion: If swallowed, do not induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. Get medical aid.
  • Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical aid.

 

Exposure Controls/Personal Protection

 

Engineering Controls

Facilities storing or utilising this material should be equipped with an eyewash facility and a safety shower. Use adequate general or local exhaust ventilation to keep airborne concentrations below the permissible exposure limits.

 

Personal Protective Equipment

  • Eyes: Wear chemical goggles.
  • Skin: Wear appropriate protective gloves to prevent skin exposure.
  • Clothing: Wear appropriate protective clothing to prevent skin exposure.
  • Respirators: A respiratory protection program that meets OSHA's 29 CFR 1910.134 and ANSI Z88.2 requirements or European Standard EN 149 must be followed whenever workplace conditions warrant a respirator’s use.

 

Regulations [6,7,8]

 

United States

 

Exposure Limit Limit Values HE Codes Health Factors and Target Organs
OSHA Permissible Exposure Limit (PEL) – General Industry
See 29 CFR 1910.1052
  • 25 ppm TWA
  • 125 ppm STEL
  • 12.5 ppm Action Level
HE1 Cancer
HE3 Cardiac and liver toxicity
HE7 Light-headedness, staggering, unconsciousness, decreased eye/hand coordination, numbness of the extremities
HE8 Central nervous system effects/narcosis
HE14 Eyes, nose, throat, skin irritation
HE17 Chemical anoxia (metabolic conversion to CO)
OSHA PEL – Construction Industry
See 29 CFR 1926.1152
  • 25 ppm TWA
  • 125 ppm STEL
  • 12.5 ppm Action Level
HE1 Cancer
HE3 Cardiac and liver toxicity
HE7 Light-headedness, staggering, unconsciousness, decreased eye/hand coordination, numbness of the extremities
HE8 Central nervous system effects/narcosis
HE14 Eyes, nose, throat, skin irritation
HE17 Chemical anoxia (metabolic conversion to CO)
OSHA PEL – Shipyard Employment
See 29 CFR 1915.1052
  • 25 ppm TWA
  • 125 ppm STEL
  • 12.5 ppm Action Level
HE1 Cancer
HE3 Cardiac and liver toxicity
HE7 Light-headedness, staggering, unconsciousness, decreased eye/hand coordination, numbness of the extremities
HE8 Central nervous system effects/narcosis
HE14 Eyes, nose, throat, skin irritation
HE17 Chemical anoxia (metabolic conversion to CO)
National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL)
See Appendix A
  • Lowest feasible concentration
  • Ca
HE1 Cancer
American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) (2001)
(Listed under dichloromethane)
  • 50 ppm
  • (174 mg/m3) TWA
  • A3, BEI
HE4 Cardiovascular changes
HE7 Neurological effects (headache, dizziness, loss of balance, memory difficulties, numbness in hands or feet)
HE8 Central nervous system effects (narcosis)
HE17 Asphyxiant, anoxiant
CAL/OSHA PELs
See Section 5202
  • 25 ppm
  • (87 mg/m3) TWA
  • 125 ppm
  • (435 mg/m3) STEL
   

 

 

Australia

 

  • 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.
  • Occupational Exposure Limits (8-hour TWA)
    • Netherlands (MAC) : 100 ppm
    • United Kingdom (OEL) : 100 ppm (MEL)
    • Germany (MAK) : 100 ppm (IIIB suspected carcinogen)
    • Sweden (TLV) : 35 ppm (skin notation)
    • France (VME) : 50 ppm
    • Switzerland (MAK) : 100 ppm

 

References

  1. http://en.wikipedia.org/wiki/Dichloromethane
  2. http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=233&tid=42
  3. http://www.epa.gov/ttn/atw/hlthef/methylen.html
  4. http://www.dhs.wisconsin.gov/eh/chemfs/fs/MthylChlrde.htm
  5. http://www.sciencelab.com/msds.php?msdsId=9948&code=SLM2677
  6. https://www.osha.gov/dts/chemicalsampling/data/CH_253450.html
  7. http://www.npi.gov.au/substances/dichloromethane/health.html
  8. http://www.eurochlor.org/media/12847/5-1-2-1_white_paper_methylene_chloride.pdf

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