Methylene chloride [factsheet]

METHYLENE CHLORIDE

Please Note: The main sources of information for this fact sheet are the Agency for Toxic Substances and Disease Registry's (ATSDR's) Toxicological Profile for Methylene Chloride and EPA's Integrated Risk Information System (IRIS), which contains information on oral chronic toxicity and the RfD, and the carcinogenic effects of methylene chloride including the unit cancer risk for inhalation exposure. Other secondary sources include the Hazardous Substances Data Bank (HSDB), a database of summaries of peer-reviewed literature, and the Registry of Toxic Effects of Chemical Substances (RTECS), a database of toxic effects that are not peer reviewed.

Environmental/Occupational Exposure

* The principal route of human exposure to methylene chloride is inhalation of ambient air. (1)

* Occupational and consumer exposure to methylene chloride 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. (1)

* Methylene chloride has been detected in both surface water and groundwater samples taken at hazardous waste sites and in drinking water at very low concentrations. (1)

Assessing Personal Exposure

* Several tests exist for determining exposure to methylene chloride. These tests include direct measurement of methylene chloride in the air and analysis of methylene chloride present in the blood and urine. It is noted that smoking and exposure to other chemicals may affect the results of these tests. (1)

Health Hazard Information

Acute Effects:

* Case studies of methylene chloride poisoning during paint stripping operations have demonstrated that inhalation exposure to very high levels can be fatal to humans. (1,2)

* Acute inhalation exposure to high levels of methylene chloride in humans has resulted in effects on the nervous system including decreased visual and auditory functions, but these effects are reversible once exposure ceases. Methylene chloride also irritates the nose and throat at high concentrations. (1,2)

* Tests involving acute exposure of animals, such as the LD₅₀ and LC₅₀ tests in rats, have shown methylene chloride to have moderate acute toxicity from oral and inhalation exposure. (3)

Chronic Effects (Noncancer):

* The major effects from chronic (long-term) inhalation exposure to methylene chloride in humans are effects on the CNS, such as headaches, dizziness, nausea, and memory loss. (1,2)

* Animal studies indicate that the inhalation of methylene chloride causes effects on the liver, kidney, and cardiovascular system. (1,2)

* The RfD for methylene chloride is 0.06 mg/kg/d based on liver toxicity in rats. (4)

* EPA has high confidence in the study on which the RfD is based because a large number of animals of both sexes were tested in four dose groups, with a large number of controls, and many effects were monitored and a dose-related increase in severity was observed; medium to low confidence in the database because only a few studies support the no-observed-adverse-effect level (NOAEL); and, consequently, medium confidence in the RfD.

* The RfC is currently under review by EPA. (4)

Reproductive/Developmental Effects:

* No studies were located regarding developmental or reproductive effects in humans from inhalation or oral exposure. (1,2)

* Animal studies have demonstrated that methylene chloride crosses the placental barrier, and lowered fetal body weights have been noted. (1,2)

Cancer Risk:

* Two studies examining the mortality incidence of workers exposed to methylene chloride did not see a statistically significant increase in deaths from cancer. (1,2)

* Animal studies have shown an increase in liver and lung cancer and benign mammary gland tumors following inhalation exposure to methylene chloride. (1,2)

* EPA considers methylene chloride to be a probable human carcinogen (cancer-causing agent) and has ranked it in EPA's Group B2. (4)

* EPA uses mathematical models, based on animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated an inhalation unit risk estimate of 4.7 H 10^-7 (m g/m³)^-1. EPA estimates that, if an individual were to breathe air containing methylene chloride at 2.0 Fg/m³* over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of breathing air containing this chemical. Similarly, EPA estimates that breathing air containing 20.0 m g/m³ would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 200.0 m g/m³ would result in not greater than a one-in-ten thousand increased chance of developing cancer. (4)

* EPA's Office of Air Quality Planning and Standards, for a hazard ranking under Section 112(g) of the Clean Air Act Amendments, has ranked methylene chloride in the nonthreshold category. The 1/ED₁₀ value is 0.013 per (mg/kg)/d and this would place it in the low category under Superfund's ranking for carcinogenic hazard. (5)

Physical Properties

* Methylene chloride is a colorless liquid with a sweetish odor. (1,6)

* The chemical formula for methylene chloride is CH₂Cl₂, and the molecular weight is 84.93 g/mol. (1)

* The vapor pressure for methylene chloride is 349 mm Hg at 20 EC, and it has an octanol/water coefficient (log K_ow) of 1.30. (1)

* Methylene chloride has an odor threshold of 250 ppm. (7)

* Methylene chloride is slightly soluble in water and is nonflammable. (1,6)

Uses

* Methylene chloride is predominantly used as a solvent in paint strippers and removers; as a process solvent in the manufacture of drugs and pharmaceutical and film coatings; and as a metal cleaning and finishing solvent in electronics manufacturing. (1)

* Methylene chloride is also used as a propellant in aerosols for products such as paints, automotive products, and insect sprays. It is used as an extraction solvent for spice oleoresins and hops and for the removal of caffeine from coffee. However, due to concern over residual solvent, most decaffeinators no longer use methylene chloride. (1)

* Methylene chloride is also approved for use as a postharvest fumigant for grains and strawberries and as a degreening agent for citrus fruit. (1)

Health Data from Inhalation Exposure

Concentration (mg/m³)	Health numbers^a	Regulatory, advisory numbers^b	Reference
1,000,000.0
_ _ _ _ 100,000.0
_ _ _ _ 10,000.0	* LC₅₀ (rats) (88,000 mg/m³) * LC₅₀ (mice) (50,020 mg/m³)		3 3
_ _ _ _ 1,000.0		* OSHA, MSHA TWA (1,750 mg/m³)	1,3
_ _ _ _ 100.0		* ACGIH TLV (175 mg/m³)	1,3
_ _ _ _ 10.0
_ _ _ _ 1.0
_ _ _ _ 0.1
_ _ _ _ 0.01
_ _ _ _ 0.001	* USEPA Cancer Risk Level (1-in-a-million excess lifetime risk) = 2 H 10^-3 mg/m³		4

See notes on following page.

ACGIH TLVCAmerican Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effects.

LC₅₀ (Lethal Concentration₅₀)CA calculated concentration of a chemical in air to which exposure for a specific length of time is expected to cause death in 50% of a defined experimental animal population.

MSHA TWACMine Safety and Health Administration's time-weighted average standard; MSHA standard expressed as an allowable exposure concentration averaged over a normal 8-h workday or a 40-h workweek.

OSHACOccupational Safety and Health Administration's standard.

^a Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.

^b Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers are nonregulatory values provided by the Government or other groups as advice.

References

1. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Methylene Chloride (Draft). U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 1991.

2. U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.

3. U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.

4. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Methylene Chloride. Office of Environmental Criteria and Assessment, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.

5. U.S. Environmental Protection Agency. Technical Background Document to Support Rulemaking Pursuant to the Clean Air ActCSection 112(g). Ranking of Pollutants with Respect to Hazard to Human Health. EPAB450/3-92-010. Emissions Standards Division, Office of Air Quality Planning and Standards, Research Triangle Park, NC. 1994.

6. The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals. 11th ed. Ed. S. Budavari. Merck and Co. Inc., Rahway, NJ. 1989.

7. J.E. Amoore and E. Hautala. Odor as an aid to chemical safety: Odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. Journal of Applied Toxicology, 3(6):272-290. 1983.