CALIFORNIA AIR RESOURCES BOARD
California Museum of Science and Industry
700 State Drive
Los Angeles, CA
December 8, 1988
88-16-1 Report on the Need for Carbon Tetrachloride 001
88-16-2 Briefing on the California Clean Air Act. 048
88-16-3 Joint Presentation of Caltrans and Air Resources
Board Staff on the Relationship Between
Transportation and Air Quality Programs.
88-16-4 Consideration of a Draft Report to the 049
Legislature on Emission Credit Systems and New
Source Review Programs as Mandated by California
Health and Safety Code Section 40709.5.
88-16-5 Report on the Federal Clean Air Act and EPA
Activities Related to Post-1987 Attainment.
Examination of the Need for Carbon Tetrachloride Control.
The staff recommends that control measures not be developed for
carbon tetrachloride at this time. This recommendation is based
on the fact that the greatest risk to the general population in
California is from the global background concentration.
Emissions from the largest individual sources, which formerly
caused "hot spot" exposures, have already been reduced to the
lowest achievable level through the application of best available
The Board identified carbon tetrachloride as a toxic air
contaminant in September 1987. State law requires that once a
substance is identified as a toxic air contaminant, the Board
staff must prepare a report on the need for and appropriate
degree of control for the substance. The staff report now under
consideration by the Board fulfills the statutory requirement.
The report was developed in consultation with air quality
management district staff and with industry representatives.
Exposure and Risk Estimates
All Californians are exposed to a global background carbon
tetrachloride concentration of approximately 0.11 parts per
billion (ppb). The background concentration is the result of a
worldwide accumulation of carbon tetrachloride from anthropogenic
emission sources. Exposure to the global background is estimated
to cause from 7 to 29 potential excess lifetime cancer cases per
million persons, or from 190 to 770 cases among California's 26.6
million residents. Emissions of carbon tetrachloride from
California sources contribute from 0.01 to 0.02 percent annually
to the global background.
When carbon tetrachloride was identified as a toxic air
contaminant, emissions from the largest source constituted a "hot
spot" exposure for persons living in the vicinity of the source.
However, the source is now controlled, and the estimated risk is
between 4 and 16 persons exposed. For the 550 people living
closest to the source, it is estimated that this exposure will
result in less than 0.01 excess lifetime cancer cases.
Emissions and Emission Trends
Statewide emissions of carbon tetrachloride have been reduced
considerably since the compound was identified as a toxic air
contaminant. Based on the 1984 inventory, the staff estimated
emissions from four major sources in California (carbon
tetrachloride production, chlorofluorocarbon (CFC) production,
grain fumigation, and chlorinated paraffin wax production) to be
approximately 85 tons per year. Emissions from these source
categories are now approximately 6 tons per year, about 90
percent below their 1984 levels. Emissions from carbon
tetrachloride and CFC production have been reduced by 90 percent
through the use of controls installed at the facilities. The use
of grain fumigants containing carbon tetrachloride has been
banned by the Environmental Protection Agency. Chlorinated
paraffin wax is no longer produced in California.
In addition to its major use in the production of CFCs, carbon
tetrachloride is used in a variety of manufacturing and
industrial processes. Approximately 3 tons per year are emitted
from carbon tetrachloride's use in petroleum refining. Emissions
from the remaining sources, which are largely uncontrolled, are
estimated to be approximately 13 tons per year. However, the
individual sources are very small, numerous, and widely
distributed. Information available to the staff indicates that
the miscellaneous uses of carbon tetrachloride are declining,
primarily because of concerns about its toxicity.
Currently, over 90 percent of the carbon tetrachloride produced
in California is used to produce CFCs. If carbon tetrachloride
is not used in the production of CFC substitutes, any future
regulation of CFCs will likely result in significant decreases in
the production of carbon tetrachloride.
The global background concentration poses the greatest risk to
the general population in California. Because California sources
contribute very little to the global background, we cannot
significantly reduce the background risk to the general
population. Sources which formerly caused "hot spot" exposures
have already applied best available control technology to reduce
emissions. Overall, emissions of carbon tetrachloride from
California sources have been reduced considerably since the
compound was identified as a toxic air contaminant.
The ARB staff does not anticipate that emissions of carbon
tetrachloride will increase in the future. However, if we
determine that public exposures are increasing, or if further
evaluation indicates that exposures are greater than currently
estimated, we will develop and bring to the Board a proposed