Toxic Air Contaminant (TAC) Identification List
Quick Reference Format
December 1999

This page last reviewed July 29, 2008

Quick Reference Format



II. Candidate TACs



Substances identified as Toxic Air Contaminants by the Air Resources Board,  pursuant to the provisions of AB 1807** and AB 2728** (includes all Hazardous Air Pollutants listed in the Federal Clean Air Act Amendments
of 1990).

Information within the square brackets refers to the corresponding subcategory on the Substances By Category version
of the list. Click on a subcategory to go it.

        Acetaldehyde [IIa]
      Acetamide [IIa]
      Acetonitrile [IVa]
      Acetophenone [IVa]
      2-Acetylaminofluorene [V]
+    Acrolein [IIa]
      Acrylamide [IIa]
      Acrylic acid [IIa]
      Acrylonitrile [IIa]
      Allyl chloride [IIa]
      4-Aminobiphenyl [V]
      Aniline [IIa]
      o-Anisidine [IVa]
      Antimony compounds (Note 4) [IIa]
*+  Inorganic Arsenic and Arsenic compounds
      (Note 4) [IIa]
      (inorganic including arsine)
*   Asbestos [IIa]
      [asbestiform varieties of serpentine (chrysotile),
      riebeckite (crocidolite), cummingtonite-grunerite
      (amosite), tremolite, actinolite, and anthophyllite]
*    Benzene (including benzene from gasoline) [IIa]
      Benzidine [V]
      Benzotrichloride [V]
      Benzyl chloride [IIa]
      Beryllium Compounds (Note 4) [IIa]
      Biphenyl [IVa]
      Bis(chloromethyl)ether [IIa]
      Bis(2-ethylhexyl)phthalate  (DEHP) [IIa]
      Bromoform [V]
*    1,3-Butadiene [IIa]
*    Cadmium and cadmium compounds (Note 4) [IIa]
      (metallic cadmium and cadmium compounds) 
      Calcium cyanamide [V]
      Caprolactam [V]
+    Captan [VI]
+    Carbaryl [VI]
      Carbon disulfide [IIa]
*    Carbon tetrachloride  (Tetrachloromethane) [IIa]
      Carbonyl sulfide [IVa]
      Catechol [IVa]
      Chloramben [V]
      Chlordane [V]
*    Chlorinated dibenzo-p-dioxins and dibenzofurans
      (Note 5) [IIa]
       2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) [IIa]
+    Chlorine [IIa]
      Chloroacetic acid [IVa]
      2-Chloroacetophenone [V]
      Chlorobenzene [IIa]
      Chlorobenzilate [IVa]
*    Chloroform [IIa]
      Chloromethyl methyl ether [V]
      Chloroprene [IVa]
+    Chromium and Compounds (Note 4) [IIa]
*    Chromium VI (Hexavalent chromium) [IIa]
      Cobalt Compounds (Note 4) [IIa]
      Coke Oven Emissions [V]
      Cresols/Cresylic acid (isomers and mixture) [IIa]
+    m-Cresol [VI]
      o-Cresol [V]
      p-Cresol [V]
      Cumene [IVa]
+    Cyanide compounds (Note 4&11) [IIa]
+    2,4-D, salts and esters [VI]
      DDE  (p,p-Dichlorodiphenyldichloroethylene) [V]
      Diazomethane [V]
      Dibenzofuran [IVa]
      1,2-Dibromo-3-chloropropane  (DBCP) [V]
      Dibutylphthalate [IVa]
+    1,4-Dichlorobenzene  (p-Dicholorobenzene) [IIa]
      3,3'-Dichlorobenzidene [IIa]
      Dichloroethyl ether  (Bis(2-chloroethyl) ether) [V]
+    1,3-Dichloropropene  (Telone)[IVa]
+    Dichlorvos  (DDVP) [VI]
      Diethanolamine  (Note 6) [IIa]
      N,N-Diethyl aniline  (N,N-Dimethylaniline) [V]
      Diethyl sulfate [V]
      3,3'-Dimethoxybenzidine [V]
      4-Dimethyl aminoazobenzene [V]
      3,3-Dimethyl benzidine (o-Tolidine) [V]
      Dimethyl carbamoyl chloride [V]
      Dimethyl formamide [IIa]
      1,1-Dimethyl hydrazine [IVa]
      Dimethyl phthalate [IVa]
      Dimethyl sulfate [IVa]
      4,6-Dinitro-o-cresol, and salts [V]
      2,4-Dinitrophenol [V]
      2,4-Dinitrotoluene [V]
      1,4-Dioxane  (1,4-Diethyleneoxide) [IIa]
      1,2-Diphenylhydrazine [V]
      Epichlorohydrin (1-Chloro-2,3-epoxypropane) [IIa]
      1,2-Epoxybutane [IIa]
      Ethyl acrylate [IVa]
      Ethyl benzene [IIa]
      Ethyl carbamate  (Urethane) [IIa]
      Ethyl chloride  (Chloroethane) [IIa]
*    Ethylene dibromide  (1,2-Dibromoethane) [IIa]
*    Ethylene dichloride  (1,2-Dichloroethane) [IIa]
      Ethylene glycol [IIa]
      Ethylene imine  (Aziridine) [V]
*+  Ethylene oxide  (1,2-Epoxyethane) [IIa]
      Ethylene thiourea [IIa]
      Ethylidene dichloride (1,1-Dichloroethane) [IIa]
      Fine mineral fibers (Note 13) [IVa]
*+  Formaldehyde [IIa]
      Glycol ethers (Note 7) [IIa]
      Heptachlor [V]
      Hexachlorobenzene [IIa]
      Hexachlorobutadiene [V]
      Hexachlorocyclopentadiene [V]
      Hexachloroethane [IIa]
      Hexamethylene-1,6-diisocyanate [IIa]
      Hexamethylphosphoramide [V]
      Hexane [IIa]
      Hydrazine [IIa]
      Hydrochloric acid [IIa]
      Hydrogen fluoride  (Hydrofluoric acid) [IIa]
      Hydroquinone [IVa]
      Isophorone [IIa]
*   Inorganic Lead and Inorganic lead compounds 
     (includes elemental lead) (Note 4 & 8) [IIa]
      Lead and compounds (Note 4) [IIa]
      (does not include elemental lead)
      Lindane [IIa]
      Maleic anhydride [IIa]
      Manganese and compounds (Note 4) [IIa]
      Mercury and compounds (Note 4) [IIa]
      Methanol [IIa]
+    Methoxychlor [VI]
+    Methyl bromide  (Bromomethane) [IIa]
      Methyl chloride  (Chloromethane) [IVa]
      Methyl chloroform (1,1,1-Trichloroethane) [IIa]
      Methyl ethyl ketone  (2-Butanone) [IIa]
      Methyl hydrazine [IVa]
      Methyl iodide  (Iodomethane) [V]
      Methyl isobutyl ketone  (Hexone) [IVa]
      Methyl isocyanate [V]
      Methyl methacrylate [IIa]
      Methyl tertiary butyl ether  (MTBE) [IIa][IIIa]
      4,4'-Methylene bis(2-chloroaniline) [IIa]
*    Methylene chloride  (Dichloromethane) [IIa]
      4,4-Methylenedianiline [IIa]
      Methylene diphenyl diisocyanate  (MDI) [IIa]
      Naphthalene [IIa]
*    Nickel and compounds (Note 4) [IIa]
      (metallic nickel & inorganic nickel compounds)
      Nitrobenzene [IIa]
      4-Nitrobiphenyl [V]
      4-Nitrophenol [V]
      2-Nitropropane [IIa]
      N-Nitroso-N-methylurea [V]
      N-Nitrosodimethylamine [IIa]
      N-Nitrosomorpholine [IIa]
      Parathion [V]
*   Particulate emissions from diesel-fueled engines
+    Pentachloronitrobenzene  (Quintozene) [IVa]
+    Pentachlorophenol [IIa]
*    Perchloroethylene  (Tetrachloroethylene) [I]
      Phenol [IIa]
      p-Phenylenediamine [IVa]
      Phosgene [IIa]
      Phosphine [IIa]
+    Phosphorus [IIa]
      Phthalic anhydride [IIa]
      Polychlorinated biphenyls  (PCBs) [IIa]
      Polycyclic organic matter  (POM) (Note 9)
      Benzo[a]pyrene  (Note 10) [IIa]
      1,3-Propane sultone [IIa]
      beta-Propiolactone [V]
      Propionaldehyde [IVa]
+    Propoxur  (Baygon) [VI]
      Propylene dichloride  (1,2-Dichloropropane) [IVa]
+    Propylene oxide [IIa]
      1,2-Propylenimine  (2-Methyl aziridine) [IVa]
      Quinoline [V]
      Quinone [V]
      Radionuclides (including radon) (Note 12) [IVa]
      Selenium and compounds (Note 4) [IIa]
      Styrene [IIa][IIIa]
      Styrene oxide [IIa]
      1,1,2,2-Tetrachloroethane [IIa]
      Titanium tetrachloride [IVa]
      Toluene [IIa]
      2,4-Toluene diamine  (2,4-Diaminotoluene) [V]
      Toluene-2,4- diisocyanate [IIa]
      o-Toluidine [V]
      Toxaphene  (Chlorinated camphene) [V]
      1,2,4-Trichlorobenzene [IVa]
      1,1,2-Trichloroethane [IIa]
*    Trichloroethylene [IIa]
      2,4,5-Trichlorophenol [V]
      2,4,6-Trichlorophenol [IIa]
      Triethylamine [IIa]
+    Trifluralin [VI]
      2,2,4-Trimethylpentane [IVa]
      Vinyl acetate [IIa]
      Vinyl bromide [V]
*    Vinyl chloride [IIa]
      Vinylidene chloride  (1,1-Dichloroethylene) [IIa]
+    Xylenes (isomers and mixture) [IIa]
            m-Xylene [IIa]
            o-Xylene [IIa]
            p-Xylene [IIa]


Substances NOT identified as Toxic Air Contaminants, known to be emitted from stationary source facilities,
which are being evaluated for entry into Category I.  Factors considered in this evaluation include carcinogenic
and noncarcinogenic health effects, emissions and exposure in California. 
  +    Aluminum and Compounds (Note 4) [IVb]
      Ammonia [IIb]
      Ammonium nitrate [IVb]
      Ammonium sulfate [IVb]
      Barium and Compounds (Note 4) [IVb]
      Benzoyl chloride [IVb]
      Bis(2-ethylhexyl)adipate [IVb]
      Bromine and compounds (inorganic) (Note 4) [IVb]
      Butyl acrylate [IVb]
+    n-Butyl alcohol [IVb]
      sec-Butyl alcohol [IVb]
      tert-Butyl alcohol [IVb]
      Butyl benzyl phthalate [IVb]
      Carbon black and Carbon black extracts [IVb]
      Chlorinated fluorocarbons [IVb]
+    Chlorine dioxide [IIb]
      Chlorophenols [IVb]
+    Chloropicrin [IIb]
+    Copper and Compounds (Note 4) [IIb]
+    Creosotes [IIb]
      Crystalline silica [IIIb]
      Cumene hydroperoxide [IVb]
      Cyclohexane [IVb]
      Decabromodiphenyl oxide [IVb]
      Dialkylnitrosamines [IVb]
      Diaminotoluene (mixed isomers) [IVb]
      Dicofol [IVb]
      Environmental Tobacco Smoke (Note 14) [IVb]
+    Ethylene [IIb]
      Gasoline vapors [IVb]
+    Glutaraldehyde [IVb]
      Hexachlorocyclohexanes [IIb]
      Hydrogen sulfide [IIb]
+    Isopropyl alcohol [IIb]
      4,4'-Isopropylidenediphenol [IVb]
      Michler's ketone [IIb]
      Molybdenum trioxide [IVb]
      Nitric acid [IIb]
      Nitrilotriacetic acid [IVb]
      Peracetic acid [IVb]
+    2-Phenylphenol [IVb]
+    Phosphoric acid [IIb]
      Propene [IVb]
+    Silver and Compounds (Note 4) [IIb]
+    Sodium hydroxide [IIb]
+    Sulfuric acid [IIb]
      Terephthalic acid [IVb]
      Thiourea [IVb]
      1,2,4-Trimethylbenzene [IVb]
+    Zinc and Compounds (Note 4) [IIb]



Substances which have already been identified by the Air Resources Board as Toxic Air Contaminants through a
comprehensive AB 1807 risk assessment and which have health values developed by the Office of Environmental
Health Hazard Assessment and approved by the Scientific Review Panel. A full risk assessment report is available


AB 1807, Statutes 1983, chapter 1047, Health and Safety Code sections 39650 et. seq.

AB 2728, Statutes 1992, chapter 1161, Health and Safety Code sections 39655 et. seq.


To be listed as a Toxic Air Contaminant, these substances will go though a comprehensive AB 1807
risk assessment.


These substances have been nominated for the development of additional health values.


These substances are active ingredients in pesticides in California. For further information regarding the
pesticidal uses of these compounds, please contact the Department of Pesticide Regulation.

Note 4:

For all listings above which contain the word "compounds" and for glycol ethers, the following applies:
Unless otherwise specified, these listings are defined as including any unique chemical substance
that contains the named chemical (i.e, antimony, arsenic, etc.) as part of that chemicalís infrastructure.

Note 5:

Chlorinated Dibenzo-P-Dioxins and Dibenzofurans: The cancer potency value for 
2,3,7,8-tetrachlorodibenzo-p-dioxin was determined for the identification of chlorinated dioxins and
dibenzofurans as toxic air contaminants in 1986. At that time, the Board identified dibenzo-p-dioxins
and dibenzofurans chlorinated in the 2,3,7, and 8 positions and containing 4,5,6, or 7 chlorine atoms as
toxic air contaminants. Since 1986, International Toxicity Equivalency Factors (ITEFs) have been developed
which are used to evaluate the cancer risk due to exposure to samples containing mixtures of chlorinated
dibenzo-p-dioxins and dibenzofurans. ITEFs are numerical factors that express the toxicity of an individual
chlorinated dibenzo-p-dioxin or dibenzofuran relative to the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin.
ITEFs are listed for 16 chlorinated dibenzo-p-dioxins and dibenzofurans.

Note 6:

Diethanolamine: There is a 1997 draft report by the National Toxicology Program that shows evidence of
carcinogenic activity in mice. (This may result in a change of the cancer classification.)

Note 7:

Glycol Ethers: Includes mono- and di-ethers of ethylene glycol, diethylene glycol, and triethylene glycol
(R (OCH2CH2)n - OR' where 

n = 1,2 or 3

R = alkyl or aryl groups

R' = R,H, or groups which, when removed, yield glycol ethers with the structure; 

R (OCH2CH)n - OH. Polymers are excluded from the glycol category.

Note 8:

Inorganic Lead: Due to information on non-cancer health effects showing no identified threshold, no
Reference Exposure Level has been developed. However, guidelines for assessing noncancer health
impacts are currently being developed by ARB staff.

Note 9:

Polycyclic Organic Matter: Includes organic compounds with more than one benzene ring, and which
have a boiling point greater than or equal to 100 oC.

Note 10:

Benzo[a]pyrene: Potency Equivalency Factors (PEF) have been developed for 24 polycyclic aromatic
hydrocarbons (PAHs). Using benzo[a]pyrene as a reference compound, a weighting scheme for PAHs
was developed in the 1994 Air Resources Board document entitled, Benzo[a]pyrene as a Toxic Air
. When a specific potency value is developed for a chemical, it should be used in place
of the PEF.

Note 11:

Cyanide Compounds: X'CN where X=H' or any other group where a formal dissociation may occur.
For example, KCN or Ca(CN)2

Note 12:

Radionuclides: A type of atom which spontaneously undergoes radioactive decay.

Note 13:

Fine Mineral Fibers: Includes mineral fiber emissions from facilities manufacturing or processing glass,
rock, or slag fibers (or other mineral derived fibers) of average diameter 1 micrometer or less.

Note 14:

Environmental Tobacco Smoke: An AB 1807-type of health assessment for Environmental Tobacco Smoke
was conducted by the Office of Environmental Health Hazard Assessment (OEHHA) and was approved by
the Scientific Review Panel on June 19, 1997. The Air Resources Board accepted the report from OEHHA
on October 23, 1997 and subsequently forwarded to the Department of Health Servicesí Tobacco Control
Program for appropriate action.

Final Staff Report
Substance by Category Format