Toxics Introduction

This page last reviewed July 30, 2008

The staff of the Air Resources Board (ARB or Board) compiled this reference report (with the assistance of staff from the Office of Environmental Health Hazard Assessment and the Department of Pesticide Regulation) on the ARB's Toxic Air Contaminant Identification List as part of the State of California's air toxics program established by Assembly Bill (AB) 1807. The report was reviewed and endorsed by the Scientific Review Panel at its June 19, 1997, meeting. This is an informational report which provides the public, interested parties, and governmental agencies, with some quick and basic reference information on a large number of substances. This report is an update to our February 1989 report, Information on Substances for Review as Toxic Air Contaminants, and is the final version of our draft report, Toxic Air Contaminant Identification List Summaries, released in January 1996 for public comment. The information presented in this report was derived from readily-available publications which are identified in the Reference Section. The report will be updated every two years, or as needed.

This report contains individual summaries of general exposure and health effects information for the 243 substances included on the AB 1807 Toxic Air Contaminant Identification List. These summaries provide readily-available information on the physical properties, sources and emissions, ambient concentrations, indoor sources and concentrations, atmospheric persistence, Air Toxics "Hot Spots" (AB 2588) risk assessment information, and potential health effects. Where available, California-specific information is included. The summaries do not revise California Environmental Protection Agency (Cal/EPA) judgments or policies about the potential for these air pollutants to harm public health.

The summaries emphasize the more common and serious health effects in providing what is generally known about the individual substances. The absence of information about a particular health effect or exposure therefore does not indicate the absence of a hazard. The pertinent information may not have been identified or the relevant studies may not have been done.

This report does provide health risk guidance values developed or approved by the Office of Environmental Health Hazard Assessment (OEHHA), Department of Pesticide Regulation (DPR), and Department of Toxic Substances Control (DTSC) under Cal/EPA (unit cancer risk factors, reference exposure levels), and the United States Environmental Protection Agency

(U.S. EPA) [reference concentrations, cancer potency factors], or provided in the California Air Pollution Control Officers Association (CAPCOA) Revised 1992 Risk Assessment Guidelines (reference exposure levels). The original documentation of these values should be consulted for additional information on how they were developed, the strength of the available evidence, and the nature of the uncertainties affecting their interpretation and application.


Many sources of information were used in the development of the report. The report is based primarily upon existing governmental exposure and health effects databases, including databases from the ARB (e.g. TAC documents, the "Hot Spots" emissions inventory, ARB's ambient air toxics monitoring network), the U.S. EPA [e.g. Hazardous Substances Data Bank (HSDB), Integrated Risk Information System (IRIS), Toxic Release Inventory (TRI)], and the World Health Organization [International Agency for Research on Cancer (IARC) Monographs On the Evaluation of Carcinogenic Risks to Humans], and the OEHHA [Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65)]. Other important sources of information were the Handbook of Chemistry and Physics and the Merck Index. Supplemental information from other reference texts, as cited, was sought for those chemicals for which information was particularly lacking. Given the general nature of the information and the reliance upon secondary sources, this report does not support risk management or clinical decisions regarding exposure. In the case where compounds are listed as compound groups, one or more representative compounds have been selected for review. In addition, more information has been provided for compounds that have been identified as TACs through the AB 1807 process. These compounds will have more detailed information than other compounds presented in this report.

The report (or this area of the website) consists of:

Structure of Individual Summaries

Each substance review is organized as follows:

Chemical Name and CAS Number - The chemical name and Chemical Abstracts Service (CAS) registry number given for each substance is from the U.S. EPA list of 189 Hazardous Air Pollutants or other sources such as the Merck Index. For compound categories (e.g., glycol ethers), CAS numbers for one or more representative compounds were selected.

Physical Properties - Physical properties of each substance include molecular weight, boiling and melting points, density/specific gravity, vapor pressure, flash point, Henry's law constant, log/octanol water partition coefficient, and a conversion factor. Some substances, because of their physical properties or lack of information available, may not have all of these factors. Synonyms are also listed which include other chemical, common, or registered trade names; these trade names are not identified as such. A detailed explanation of the physical properties is provided in the Glossary of Terms.

Sources and Emissions - This section provides information on sources, estimated emissions, and uses at facilities in California. Most of this information was obtained from ARB's Air Toxics Emissions Data System (ATEDS) database for stationary sources as required under the AB 2588 Air Toxics "Hot Spots" Program. The ATEDS database is dynamic and is continuously being updated to include the most recent emissions information available. Although comprehensive, the ATEDS database does not include emissions from facilities that are exempt from the reporting requirements pursuant to the Air Toxics "Hot Spots" Program. Emissions data provided from the ATEDS database were rounded to 2 significant figures in most cases (1 significant figure in others). Where available, ARB mobile source information is included in the report and a brief explanation on a substances natural occurrence is also provided.

Ambient Concentrations - Information on ambient air monitoring for each substance is found in this section. If available, California-specific monitoring data from the ARB monitoring network or special studies conducted in California are provided. Additional nationwide ambient data are provided, where possible, for those compounds designated as Hazardous Air Pollutants by the U.S. EPA.

Indoor Sources and Concentrations - This section lists the major sources of indoor exposure of each substance and provides, where available, California-specific indoor air concentration data. The U.S. EPA data for indoor measurements throughout the nation may also be included. Indoor concentrations may not be comparable to outdoor concentrations due to

differences in methods of calculating indoor concentrations (i.e., geometric mean vs. arithmetic mean), sampling periods, and the location of sources.

Atmospheric Persistence - Readily-available information on the atmospheric lifetime, half-life, and physical removal of each substance from the atmosphere is summarized in this section. More information on atmospheric persistence is provided in the Explanation of Atmospheric Persistence.

AB 2588 Risk Assessment Information - This section contains information from the Air Toxics "Hot Spots" Program (AB 2588) risk assessment database on cancer risk and non-cancer health effects from facility risk assessments in California. This database was compiled by the OEHHA from risk assessments submitted by local air pollution control districts as a way to track substances under the AB 2588 program. This report includes the results of a facility's risk assessment for each substance that contributed to a total cancer risk of at least 10 in a million and/or a total non-cancer (acute or chronic) hazard index greater than 1. Data from OEHHA's risk assessment database do not necessarily represent final district approval, and are subject to change.

Health Effects - This section contains brief toxicological information and emphasizes the inhalation route of exposure. The information is derived from secondary sources and is not meant to be comprehensive. The health effects information is subdivided into non-cancer and cancer sections.

The non-cancer subsection contains the more serious or common health effects observed in the epidemiological or animal studies. The apparent emphasis on acute health effects data, as opposed to chronic health effects data, reflects the fact that much more is known about the adverse health effects of acute exposures than chronic exposures. Much of the information comes from the Hazardous Substances Data Bank (HSDB), Integrated Risk Information System (IRIS), and the U.S. EPA Health Effects Notebook for Hazardous Air Pollutants. Information also comes from existing documents prepared by the OEHHA, including the list of substances identified as reproductive toxicants under the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65) in the Proposition 65 List of Chemicals Known to the State to Cause Cancer or Reproductive Toxicity.

Other identified reference texts were used to supplement the available information on non-cancer human health effects. These texts included an occupational reference text, Chemical Hazards of the Workplace (Proctor, 1988). Much of our understanding of the adverse health effects of chemicals on human health stems from occupational studies. Workers are usually exposed to levels many times greater than the general public. A clinical poisoning text, Poisoning and Drug Overdose (Olson, 1994), was used as a reference since acute over-exposures are another important source of human health effects information. A hazardous materials reference text, Handbook of Environmental Fate and Exposure for Organic Chemicals

(Sittig, 1991) was also relied upon. Occasionally, other sources of information were consulted as indicated in the individual citations.

The non-cancer subsection contains any available inhalation health risk guidance values developed or approved by the Cal/EPA or the U.S. EPA, or provided in the California Air Pollution Control Officers Association's (CAPCOA) Air Toxic "Hot Spots" Program Revised 1992 Risk Assessment Guidelines, October 1993. (Senate Bill 1731, approved in

September 1992, requires the OEHHA to prepare and adopt risk assessment guidelines that will become the standard for risk assessments prepared under the "Hot Spots" Program. The guidelines will contain acute and chronic Reference Exposure Levels and cancer potency numbers, and upon approval of these guidelines, this report will be updated. The OEHHA's guidelines will essentially replace CAPCOA's guidelines but may include some of the same health risk guidance values). The U.S. EPA Reference Dose (RfD) is given when no inhalation Reference Concentration (RfC) is available.

The cancer subsection presents a brief summary of information and the overall evaluations and classifications of carcinogenic potential developed by the OEHHA, the U.S. EPA, and IARC (see Appendix E for IARC/U.S. EPA classification criteria). The subsection includes the unit cancer risk estimates developed, or approved by, the Cal/EPA (OEHHA, the Department of Pesticide Regulation, and the Department of Toxic Substances Control), and the U.S. EPA. A unit risk is the estimated risk of developing cancer from a 70-year lifetime exposure to an airborne concentration of one microgram per cubic meter of a substance. These estimates involve a number of different assumptions and have a great deal of associated uncertainty. Typically, they represent the risk calculated from the upper 95% confidence bound of the cancer potency measure. These unit risk values have been used as a basis for regulatory actions, and the majority have undergone peer review and in many cases rigorous regulatory review.

This section also includes information on those compounds for which "no significant risk levels" have been established by California under Proposition 65. When an agent has been identified by the State of California as being a carcinogen under Proposition 65, a warning is required if exposures exceed no significant risk levels (defined as one excess case of cancer per 100,000 individuals exposed over a 70-year lifetime). These levels are found in the Proposition 65 List of Chemicals Known to the State to Cause Cancer or Reproductive Toxicity.


The licensing and regulation of pesticides for sale and use in California are the responsibility of the Department of Pesticide Regulation (DPR). Information presented in this report regarding the permitted pesticidal uses of these compounds has been collected from pesticide labels registered for use in California and from DPR's pesticide databases. The information reflects pesticide use and permitted use in California as of October 15, 1996. The Additional Pesticide Information from DPR contains the following information specific to our document:

For further information regarding the pesticidal uses of these compounds, please contact the Pesticide Registration Branch of DPR at (916) 445-4300.


On June 14, 1996, the Board approved the removal of acetone from Category III of the

AB 1807 Toxic Air Contaminant Identification List. The Board's action to remove acetone from the Toxic Air Contaminant List followed a U.S. EPA decision to exempt acetone from the list of toxic chemicals under the Superfund Amendments and Reauthorization Act, Title III, and was in response to a petition from the Chemical Manufacturers Association. Because of this action, the fact sheet on acetone has also been removed from this summary document.

For additional information, a copy of the staff report on acetone, or to obtain additional copies of the Toxic Air Contaminant Identification List Summaries report, please contact the Air Quality Measures Branch at (916) 445-6318 or visit our homepage at

Toxics Program