1991-06-00 Air Toxics Update #7

This page last reviewed July 30, 2008


Air Toxics Update #7




This Update is the seventh in a series of publications summarizing recent activities in California's Air Toxics Program. It covers the Toxic Air Contaminant Identification and Control Program, the Air Toxics Hot Spots Assessment Program, the Motor Vehicle Toxics Program, and the Landfill Gas Testing Program. The six previous Updates are available in the ARB public information office.


Below are the 14 substances which have been identified by the ARB as toxic air contaminants (TACs). Highlighted in red are the four compounds that were identified as TACs in 1990, and a short discussion of these are in this update.

  • asbestos*
  • benzene*
  • cadmium
  • carbon tetrachloride
  • chlorinated dioxins / furans*
  • chloroform
  • ethylene dibromide
  • ethylene dichloride
  • ethylene oxide*
  • hexavalent chromium*
  • inorganic arsenic
  • methylene chloride
  • trichloroethylene
  • vinyl chloride

Control decisions have been made for the eight TACs that are underlined. A total of six control measures have been adopted for the five compounds marked with an asterisk. Two control measures have been adopted for hexavalent chromium. An emphasis on encouraging pollution prevention has been used whenever feasible. The seven control measures, when fully in place and enforced, will affect over 2,000 sources statewide and will lead to pollution reductions of over 90 percent in most cases.

Three of the control measures were adopted in 1990. A short discussion of each is in this update. For information on substances identified for which control measures were adopted in 1989 or earlier, please contact ARB's Public Information Office for previous editions of Toxics Updates.


Inorganic Arsenic

At its July 1990 hearing, the Board identified inorganic arsenic as a TAC and determined that it is a carcinogen without an identifiable threshold. Initial estimates of primary sources of inorganic arsenic in California include combustion processes such as fireplaces, woodstoves, wood-fired boilers, and internal combustion engines.

Threshold -- a level of pollutant exposure below which no adverse health effects are likely to occur.

The Department of Health Services (DHS) estimate of the most plausible cancer risk from inorganic arsenic is approximately three excess cancers per million people continuously exposed to 1 nanogram per cubic meter. This corresponds to an excess of 190 potential cancer cases for a California population of 30 million people exposed to average ambient concentrations over a 70-year lifetime. Hot spot concentrations of inorganic arsenic have been measured to be about ten times higher than average ambient concentrations.

Cancer Risk -- An estimate of the likelihood of getting cancer.

Nanogram -- A unit of weight equal to one billionth of a gram (one gram equals about 1/5 of a nickel).

Cubic Meter -- A volume equivalent to the inside of a cube that is about 39" high, by 39" wide, by 39" deep.


At its October 1990 hearing, the Board identified trichloroethylene (TCE) as a TAC and determined that it is a carcinogen without an identifiable threshold. Available information indicates that degreasing operations are a major source of TCE emissions in California. Other sources of emissions include paints and coatings, adhesive formulations, sewage treatment plants, polyvinyl chloride production and distribution facilities, and solvent reclamation.

The DHS estimate of most plausible cancer risk from lifetime exposure to 1 microgram per cubic meter of TCE is approximately two excess cases per million people exposed. This translates to an excess of 73 potential cancer cases for a California population of 30 million people exposed to average ambient concentrations over a 70-year lifetime. Hot spot and indoor concentrations have been estimated to be two to five times higher than average ambient concentrations.

Vinyl Chloride

At its December 1990 hearing, the Board identified vinyl chloride as a TAC and determined that it is a carcinogen without an identifiable threshold. Although vinyl chloride is not produced in California, it is used in the production of polyvinyl chloride (PVC) products for the construction, packaging, and electrical industries. Preliminary investigation indicates that landfills, sewage treatment plants, and PVC production and fabrication facilities are sources of vinyl chloride in California.

The most plausible estimate of cancer risk for a lifetime of exposure to 1 microgram per cubic meter of vinyl chloride is estimated by DHS to be approximately 78 excess cases per million people exposed. In California, vinyl chloride has only been detected around hot spot emission sources, such as landfills. Using average data from one well-studied landfill, it has been estimated that a continuous 70-year lifetime exposure could result in 26 potential excess cancer cases for the surrounding population of 4 million people.


At its December 1990 hearing, the Board identified chloroform as a TAC and determined that it is a carcinogen without an identifiable threshold. Available data indicate that emission sources of chloroform include pharmaceutical manufacturing, laboratory use, perchloroethylene production, and the chlorination of water. Water chlorination processes include sewage treatment plants, cooling towers, pulp and paper mills, and bleach used for domestic cleaning and laundry.

The most plausible estimate of risk for contracting cancer for a lifetime of exposure to 1 microgram per cubic meter of chloroform is estimated by the DHS to be approximately five excess cases per million people exposed. Assuming a California population of 30 million people exposed to average ambient concentrations over a 70-year lifetime, an excess of 23 potential cancer cases could result. Indoor concentrations have been estimated to be as much as ten times higher than average ambient concentrations.



In April 1990, the ARB approved a control measure to reduce asbestos emissions from serpentine rocks used in unpaved surfacing applications. This included uses in unpaved roads, parking lots, playgrounds, and driveways. Serpentine rock in California may contain 2 to 20 percent asbestos. However, in some cases, the asbestos content can be as high as 90 percent. Asbestos fibers from serpentine rock can be released into the atmosphere through human disturbances (for instance, vehicle traffic) or by weathering and wind.

The control measure prohibits the use of serpentine rock for unpaved surfaces if the serpentine rock has an asbestos content greater than 5 percent. Sellers or suppliers of serpentine rock used for unpaved surfaces are required to determine the asbestos content of the material, and to list on receipts of sales the asbestos content of the serpentine material, the amount of material sold, and the dates the material was tested and sold.

This control measure will eliminate the use of serpentine rock with high asbestos content on all new and existing unpaved surfaces. Through maintenance operations, existing asbestos- containing serpentine material will gradually be replaced with non-serpentine material. This will, over time, reduce asbestos emissions and the potential health risk to people living near unpaved serpentine-covered surfaces. The control measure will not affect the use of serpentine material for non-surfacing applications such as road base, fill, or other applications where the serpentine material is covered.


In July 1990, the ARB approved a control measure to reduce dioxins emissions from medical waste incinerators. The development of this control measure was given high priority because many of the 146 medical waste incinerators in California have no emission controls and are located in residential areas.     

The control measure specifies different requirements for incinerators based on the amount of waste burned. All facilities are required to comply with operator training and record-keeping requirements. Facilities burning more than 25 tons per year (T/Y) of waste are also required to reduce dioxins emissions by 99 percent, or meet a dioxins limit of 10 nanograms per kilogram of waste burned. This would be verified with two annual source tests to determine compliance with the emission limits. Facilities burning between 10 and 25 T/Y of waste do not have to meet the dioxins emissions limit, but are required to conduct an initial dioxins source test. Facilities burning less than 10 T/Y of waste are required to comply with the operator training and record-keeping requirements only.

The ARB staff expects about two-thirds of the medical waste incinerators in the state will be able to meet the control measure's requirements and so will have the option of coming into compliance and continuing operation.

Ethylene Oxide

Ethylene oxide (EtO) was identified by the ARB as a TAC in November 1987 (see Update #4). In California, most ethylene oxide is used to sterilize medical devices and products, and to fumigate foodstuffs. We estimate in 1989, over 800,000 pounds of EtO were used for sterilization and fumigation in California. At most EtO-using facilities, virtually all of the EtO was vented to the atmosphere after the sterilization process was completed. Because of the potential for harm to public health from these uncontrolled emissions, ARB staff proposed a control measure that would require EtO-using facilities to cut emissions to the maximum extent achievable using available technology.

During the development of the proposed control measure, ARB staff held several informal meetings to discuss the proposal with industry and the public. At a formal public hearing in May 1990, the Board approved the "Ethylene Oxide Airborne Toxic Control Measure for Sterilizers and Aerators". The measure requires facilities using EtO as a sterilant gas to meet emission control requirements based on annual usage of EtO; larger users have to meet higher control levels. For example, small and medium EtO users must cut EtO emissions from their sterilizers by at least 99 percent, whereas large users must reduce emissions by 99.8 percent. When fully implemented and enforced by the air districts, the measure will cut EtO emissions by more than 98 percent, without interfering with the use of EtO in important health care-related applications.


In September of 1987, the Governor of California signed into law Assembly Bill 2588, creating the Air Toxics "Hot Spots" Information and Assessments Program. Under the Hot Spots Program, stationary sources are required to report the type and quantity of certain toxic substances their facilities routinely release into the air. The goals of the Hot Spots Program are to collect emissions data, to identify facilities having localized impacts, to ascertain health risks, and to notify nearby residents of significant health risks. Air releases of interest are those that result from the routine operation of facilities or that are predictable.

The process established by the Hot Spots Program requires owners or operators of specified facilities to prepare and submit to air pollution control districts an air toxics emission inventory plan and a subsequent emission inventory report. The district is then required to prioritize facilities subject to the program as high, intermediate, or low priority taking into consideration factors including the emissions of listed substances, the potency and toxicity of emitted substances, and the proximity of the facility to potential receptors.

All facilities that are designated as high priority are required to prepare and submit to the district a health risk assessment in accordance with a specified schedule. The district may require additional facilities, beyond those designated as high priority, to submit a risk assessment. The risk assessment must be reviewed by the California Department of Health Services and approved by the district. If the district determines significant health risks are associated with emissions from the facility, the facility operator must notify all exposed individuals of the results of the risk assessment. The emissions data will also be used in the AB 1807 TAC program for identifying, establishing priorities for, and controlling TACs.

The ARB is required to develop a program to make the emission data collected under the Hot Spots Program available to the public. If requested, districts must make health risk assessments available for public review. Districts must also publish annual reports summarizing the health risk assessment program, ranking facilities according to the cancer risk posed, identifying facilities posing noncancer health risks, and describing the status of development of control measures, if any.

The Hot Spots Program will complement ARB's existing air toxics control program by locating sources of substances not currently under evaluation and by providing exposure information necessary for establishing priorities and regulatory action.

Emission Inventory Reports

The Air Toxics Hot Spots Act phases facilities into the program over several years. It is estimated approximately 3,700 facilities are required to submit emission inventories in the first reporting phase. By early 1991, the majority of these facilities have submitted emission inventory reports to the local air pollution control districts. The districts will review the reports and ensure that they comply with the Emission Inventory Criteria and Guidelines Regulation adopted by the ARB in 1989 and amended in 1990.

The Emission Inventory Criteria and Guidelines Regulation provides the specifications for the emission inventory plans and reports. Ninety days after the districts approve the reports, the reported data is to be transmitted to the ARB by the districts for compilation into a statewide air toxics emission inventory. The ARB has developed the Air Toxics Emission Data System (ATEDS) to compile and maintain this information and to make it available to the public. For data received from the districts in early 1991, the ARB staff expects to complete preliminary checks and make the data available to the public in the summer of 1991.

Under the Hot Spots Program, facility operators are required to update their emission inventories every two years. The amendments to the Emission Inventory Criteria and Guidelines Regulation specify the procedures for these biennial updates. The amendments also implement additional requirements in the Act to include into the Hot Spots Program particular classes of facilities emitting relatively small amounts of criteria pollutants and having a potential to cause or contribute to toxic "hot spots". The identified classes and the applicable requirements are included in the amended regulation and are summarized in a report to the Legislature approved by the Board in June 1990.

AB 2588 Facility Prioritization and Risk Assessment

By early 1991, the majority of local air pollution control districts had initiated prioritizing facilities reporting under the Hot Spots Program for purposes of risk assessment. To assist districts with this task, the California Air Pollution Control Officers Association (CAPCOA) AB 2588 Risk Assessment Committee developed facility prioritization guidelines. This committee consists of members representing 11 air pollution control districts, the DHS, and the ARB.

The CAPCOA AB 2588 Facility Prioritization Guidelines consider factors such as emissions of toxic substances, the potency and toxicity of emitted substances, and the proximity of potential receptors to score facilities reporting under the program. The district uses the resulting facility scores to identify which facilities are high, intermediate, and low priority. All those facilities designated as high priority are required to prepare and submit to the district a health risk assessment according to a specified schedule. The district may require additional facilities, beyond those designated high priority, to prepare and submit to the district a health risk assessment.

As of February 1991, well over one thousand facilities statewide had been prioritized by districts. Of those facilities, several hundred will be required to submit risk assessments.

Submitted risk assessments are reviewed by the DHS and the local air districts. After risk assessments are approved by the districts, facilities are evaluated to determine if they present significant health risks to the public. If a district determines that a facility does pose a significant risk, the facility operator is required to provide notice to all exposed persons regarding the results of the risk assessment in accordance with notification procedures established by the district.


Assembly Bill 4392, enacted in 1988, required the Board to: (1) assess and prioritize known and suspected TACs emitted by vehicular sources and (2) develop a plan for reducing public exposure to motor vehicle toxics. The first requirement involved the preparation of a report addressing the nature, extent, and severity of exposure to toxic substances emitted by motor vehicles. This report was considered by the Board at a public hearing on June 8, 1989. It identified five substances as accounting for 98 percent of the cumulative statewide number of estimated cancer cases attributable to motor vehicles. In order of decreasing risk contribution, these substances are benzene, 1,3-butadiene, diesel particulate, formaldehyde, and acetaldehyde. All five have been either formally identified or are under review for identification as a TAC.

The second requirement of AB 4392 directed the Board to reassess its schedule for reviewing toxic substances. The Board is to give appropriate emphasis to motor vehicle toxics where it is warranted, and to consider a plan for reducing exposure to motor vehicle toxics. The Board adopted a control plan on June 21, 1990.

The principal elements of the control plan include control measures specifically targeted at motor vehicle toxics, as well as measures contained in the 1990 update to "California's Mobile Source Plan for Continued Progress Toward Attainment of the State and National Ambient Air Quality Standards" (approved by the Board in December 1990). Large emission reductions of non-methane hydrocarbons are projected under the Mobile Source Plan, especially from the low-emission vehicle / clean fuels portion of the plan. These emission reductions are also expected to result in a proportional and substantial emission / risk reduction of toxic substances emitted by motor vehicles.


In September 1990, the ARB approved the regulations for low-emission vehicles and clean fuels. These regulations require vehicle manufacturers to produce low-emission vehicles meeting substantially more stringent exhaust emission standards and ensure that clean fuels would be available to the consumer at retail outlets.

Specifically, four categories of vehicles would be created by the regulations: transitional low-emission vehicles, low-emission vehicles, ultra-low-emission vehicles and zero-emission vehicles. For each of these vehicle categories, progressively more stringent standards for non-methane organic gases, carbon monoxide, oxides of nitrogen and formaldehyde are established. Beginning in 1994, low-emission passenger cars and light-day trucks will be phased in under an emission averaging program. Phase-in of low-emission medium-duty vehicles will begin in 1998.

The regulations also require that if clean fuels are used to certify low-emission vehicles that these fuels will be available to the public. Some retail service station owners will be required to install clean fuel dispenser equipment; make the fuel available for purchase; show that they, or a third party, are capable of supplying clean fuels in quantities needed at the retail level; and market clean fuels the same way they market gasoline.

Implementation of these regulations will benefit air quality throughout the state. By the year 2010, it is estimated that vehicular emissions of non-methane organic gases and nitrogen oxides will be reduced by 18 and 28 percent, respectively. In addition, various toxic substances including benzene, 1,3-butadiene, formaldehyde, acetaldehyde, and diesel particulate will be reduced. It is estimated that the reduction of these toxic emissions will prevent 20 to 40 potential cancer cases per year statewide.


Concern that landfills of solid waste and hazardous waste may be sources of toxics emissions to the outdoor air led to a requirement that all actively operating and some inactive closed landfills must carry out testing to identify potential public health problems. Landfill operators must test for ten contaminants in addition to methane. Testing locations include points within the landfill beneath the soil surface, at the landfill surface, and in the outdoor air at the edge of the landfill. Any gas moving away from the landfill underground was also required to be tested.

To date more than 80 percent of the landfills (including some inactive landfills) have been tested. During 1990, the staff analyzed summaries of the testing data submitted to air districts around the state. Air contaminants were found beneath landfill soil surfaces for the majority of the landfills tested; however, the gases were found less often at the surface and in the outdoor air at the edge of the site. Landfills where gases were detected are being further investigated to see if they pose a threat to public health, through the use of evaluation guidelines developed in cooperation with the air pollution control districts. Gas was also detected underground moving away from 20 percent of the landfills. California's Integrated Waste Management Board is investigating those sites.

ARB staff, in cooperation with the air districts, developed a suggested control measure to reduce emissions from landfills. The measure can be used by local districts wishing to implement such a rule and specifies controls and testing requirements.


Authority to regulate pesticides in ambient air is vested in the California Department of Food and Agriculture (DFA). At the request of the DFA, ARB measures concentrations of pesticides present in the outdoor air. The DFA uses ARB measurements, data from other air sampling studies, and health information to decide whether these pesticides should be identified and controlled as TACs.

Since the program began, the ARB has conducted air monitoring for 15 pesticides. Monitoring is conducted in the county or counties where it is most heavily used, near fields where applications are expected, and during the time of year when it is most heavily used.

As a result of ARB pesticide monitoring efforts, DFA has been able to take one compound, ethyl parathion, to the Scientific Review Panel on Toxic Air Contaminants. In addition, ARB pesticide monitoring data showing Telone concentrations above levels that appear to present a health threat was used by DFA as part of the basis for suspending the permits of all users of Telone in California.


Companies that treat, store, or dispose of hazardous waste, and have emissions to the outdoor air, fall under the regulatory jurisdiction of the local air pollution control districts, the ARB, and the DHS. These agencies work together when new facilities apply for a permit to construct and air pollution is a concern, or when a contaminated site is being cleaned up. Cooperation and information sharing is described in a formal agreement between the state agencies.

The ARB staff provides technical assistance to the local air districts and the DHS Toxics Substances Control Program. Questions most often asked are about how to conduct proper ambient air monitoring, modeling of possible emissions to see if significant concentrations will be present in the air, and the effectiveness of control equipment in reducing air emissions. This assistance is an ongoing activity of the ARB.


Compounds expected to be considered for identification by the Board over the next year include nickel, perchloroethylene, 1,3-butadiene, and formaldehyde. During this same period, control measures for motor vehicle toxics and toxic metals are scheduled to be considered by the Board. For further information about ARB's TAC program, please contact:

Air Resources Board
Stationary Source Division
P.O. Box 2815
Sacramento, CA 95812
(916) 445-0650


Air Toxics Updates