AQ Monitoring Results:
Crockett: Carbon Tetrachloride at John Swett
This page last reviewed September 27, 2010
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 1998-2000 was 0.1 ppb (parts
per billion), with values ranging from 0.01 ppb to 0.2 ppb. The current routine monitor closest to Crockett is in Fremont. Relative to the statewide average, the Fremont 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 John Swett 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 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 22% 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.