Carbon Tetrachloride at Fremont School
This page last reviewed October 19, 2010
Background
At normal temperature, carbon tetrachloride is a nonflammable, colorless, clear, heavy liquid. Volatile organic
compounds are readily released into the air from this heavy liquid, which has a sweetish, aromatic odor. California
under Proposition 65 and Assembly Bill 1807 has identified carbon tetrachloride as a cancer-causing compound. Inhalation
of carbon tetrachloride by humans has resulted in hepatitis and kidney damage as well as central nervous system
effects of headache, nausea, vomiting, lethargy, and weakness. The ARB has taken regulatory actions to reduce carbon
tetrachloride emissions.
Carbon tetrachloride does not naturally occur in the environment. The major identified emission sources of carbon
tetrachloride in California are: 1) carbon tetrachloride production; 2) pesticide/grain fumigant usage; 3) chlorinated
paraffin wax production; and 4) fluorocarbon production. Of these four sources, carbon tetrachloride production
and pesticidal/grain fumigant usage accounted for over 80 percent of the estimated emissions. Other emission sources
of carbon tetrachloride include oil companies, scientific laboratories, organic chemical manufacturing companies,
and publicly owned treatment works. The statewide emissions are small, and background concentrations account for
most of the health risk. Carbon tetrachloride is no longer used for dry cleaning purposes, as a grain-fumigant
and a pesticide. However, carbon tetrachloride is stable in the presence of air and light, and thus has a long
residence time in the atmosphere. The use of carbon tetrachloride in products to be used indoors has been discontinued
in the United States. Due to a very small number of sources, carbon tetrachloride levels throughout the state are
constant and attributable to background.
Ambient Monitoring Results
Ambient levels of carbon tetrachloride are monitored at approximately twenty sites in the California air toxics
monitoring network. The statewide average concentration of carbon tetrachloride during 1998-2001 was 0.1 ppb (parts
per billion), with values ranging from 0.01 ppb to 0.2 ppb. Relative to the statewide average, the Fresno regional
average concentration was comparable with values around 0.1 ppb for the same time period. Carbon tetrachloride
does not have much seasonal variability because it is stable in sunlight and has a low water solubility.
The ambient monitoring results at Fremont School are provided here:
- A graph comparing the monthly summaries of carbon tetrachloride in the community with historical statewide and regional levels
- A table of summary statistics
- Raw data in Excel format
Cancer Risk
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. Carbon tetrachloride represents approximately 12% of the potential cancer risk of the nine measured compounds, excluding diesel particulate matter. Carbon tetrachloride represents approximately 4% of the potential cancer risk of the nine measured compounds and the estimated diesel particulate matter.
