AQ Monitoring Results:
Crockett: Methylene Chloride at John Swett
This page last reviewed September 27, 2010
One of the important contributors to health risk from air pollution, methylene chloride (dichloromethane) is a volatile, nonflammable, and colorless liquid with a sweetish chloroform-like odor. Volatile organic compounds are readily released from this liquid into the air. California has determined under Assembly Bill 1807 and Proposition 65 that methylene chloride is a cancer-causing compound. Through inhalation, methylene chloride vapors are irritating to the eyes, respiratory tract, and skin. It is also a central nervous system depressant, causing decreased visual and auditory functions, and possibly headache, nausea and vomiting. At high exposures, methylene chloride can cause
pulmonary edema, cardiac arrhythmias, and loss of consciousness. The ARB has taken regulatory actions to reduce methylene chloride emissions.
Methylene chloride is used as a solvent, a blowing and cleaning agent in the manufacturing of polyurethane foam and plastic fabrication, and in paint stripping operations. Paint removers account for the largest use of methylene chloride in California. The primary stationary sources that have reported emissions of methylene chloride in California are plastic product manufacturers, manufacturers of synthetics, and aircraft and parts manufacturing, which account for approximately 61% of total emissions. Many manufacturers of consumer products are voluntarily phasing out their use of methylene chloride. In the case of aerosol paints, use will be restricted by an Air Resources Board (ARB) regulation. In 2000, the ARB adopted a control measure to eliminate the use of methylene chloride in degreasers for automotive maintenance and repairing. The statewide annual average concentrations of methylene chloride declined 38% from year 1990 to year 2000.
Ambient Monitoring Results
Ambient levels of methylene chloride are routinely monitored at approximately twenty sites in the California air toxics monitoring network. The statewide average concentration of methylene chloride during 1998-2000 was 0.6 ppb (parts per billion), with values ranging from 0.5 ppb to 8.3 ppb. The limit of detection for methylene chloride
is 1 ppb, so when levels fall below this level, the observed value is 0.5 ppb. In the absence of monitored high levels of methylene chloride, monthly averages will remain around 0.5 ppb. The current routine monitor closest to Crockett is in Fremont. Relative to the statewide average, the Fremont region was 23% higher, with an average concentration of 0.7 ppb for the same time period.
The ambient monitoring results at John Swett are provided here:
- A graph comparing the monthly summaries of methylene chloride at the community with historical statewide and regional levels
- A table of summary statistics
- Raw data in Excel format
Cancer risk is the number of excess cancer cases among a million people if the people are exposed to levels of a toxic air pollutant over 70 years. Nine measured compounds, excluding diesel particulate matter, make up most of the estimated cancer risk at John Swett. Methylene chloride represents less than 1% of the potential cancer risk of the nine measured compounds, excluding diesel particulate matter. Methylene chloride represents less than 1% of the potential cancer risk of the nine measured compounds and the estimated diesel particulate matter.