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Environmental Protection Agency's Reference Concentrations (RfCs)

Air toxic image

This ranking is based on EPA's Reference Concentration (RfC). A RfC is an estimate of a continuous inhalation exposure concentration to people (including sensitive subgroups) that is likely to be without risk of deleterious effects during a lifetime. An RfC is reported in milligrams of pollutant per cubic meter of air (mg/m3 ).

The following are the pollutants in the 1999 Alaska Air Toxics Emission Inventory considered to be some of the most toxic for non-cancer effects as they correspond to the ten lowest reference concentrations:

Rank Chemical Name RfC mg/m3 Comments
1 Chromium VI chromic acid mists and dissolved Cr (VI) aerosols (PDF) 0.000008 N/A
2 Cadmium compounds (PDF) 0.00001 RfC from California Environmental Protection Agency
2 Hexamethylene-1,6-Diisocyanate (PDF) 0.00001 N/A
3 Acrolein (PDF) 0.00002 N/A
3 Beryllium Compounds (PDF) 0.00002 N/A
4 2-Chloroacetophenone (PDF) 0.00003 N/A
4 Arsenic Compounds-inorganic including arsine (PDF) 0.00003 RfC from California Environmental Protection Agency
5 Arsine (PDF) 0.00005 N/A
5 Manganese Compounds (PDF) 0.00005 N/A
5 Nickel Compounds (PDF) 0.00005 RfC from California Environmental Protection Agency
6 Chlorine (PDF) 0.00006 RfC from California Environmental Protection Agency
7 2,4-Toluene Diisocyanate (PDF) 0.00007 RfC for mixture of Toluene 2,4- and 2,6-Diisocyanate
7 Phosphorus (PDF) 0.00007 RfC from California Environmental Protection Agency
8 Chromium VI Particulates (PDF) 0.0001 N/A
9 1,2-Dibromo-3-Chloropropane (PDF) 0.0002 N/A
9 Antimony Compounds (PDF) 0.0002 RfC for Antimony Trioxide
9 Ethylene Dibromide (Dibromoethane) (PDF) 0.0002 N/A
9 Hexachlorocyclopentadiene (PDF) 0.0002 N/A
9 Hydrazine (PDF) 0.0002 RfC from California Environmental Protection Agency
10 Lindane - all isomers (PDF) 0.0003 RfC from California Environmental Protection Agency
10 Elemental Mercury (PDF) 0.0003 N/A
10 Phosgene (PDF) 0.0003 RfC from California Environmental Protection Agency
10 Phosphine (PDF) 0.0003 N/A

The following pollutants in the 1999 Alaska Air Toxics Emission Inventory also have RfCs:

  • 1,1,2-Trichloroethane
  • 1,2,4-Trichlorobenzene
  • 1,2-Epoxybutane
  • 1,3-Butadiene
  • 1,3-Dichloropropene
  • 1,4-Dichlorobenzene(p)
  • 1,4-Dioxane (1,4-Diethyleneoxide)
  • 2,4-Dinitrotoluene
  • 2-Butoxyethanol
  • 2-Ethoxyethanol
  • 2-Methoxyethanol
  • 2-Nitropropane 
  • 4,4'-Methylenedianiline
  • Acetaldehyde 
  • Acetonitrile
  • Acrylamide
  • Acrylic Acid
  • Acrylonitrile 
  • Allyl Chloride
  • Aniline
  • Benzene (including benzene from gasoline)
  • Benzidine
  • Bis(2-ethylhexyl)phthalate (DEHP)
  • Carbon Disulfide
  • Carbon Tetrachloride
  • Chlordane
  • Chlorobenzene
  • Chloroform 
  • Chloroprene
  • Cresols/Cresylic Acid (isomers and mixture)
  • Cumene
  • Cyanide Compounds
  • Dichlorvos
  • Diethanolamine
  • Dimethyl Formamide 
  • Elemental Selenium
  • Epichlorohydrin (1-Chloro-2,3-epoxypropane)
  • Ethyl Benzene
  • Ethyl Chloride (Chloroethane)
  • Ethylene dichloride (1,2-Dichloroethane) 
  • Ethylene Glycol
  • Ethylene Oxide
  • Ethylene Thiourea
  • Ethylidene dichloride (1,1-Dichloroethane)
  • Hexachlorobenzene
  • Hexachlorobutadiene
  • Hexachloroethane
  • Hexane
  • Hydrochloric Acid
  • Hydrogen Fluoride (Hydrofluoric acid)
  • Isophorone
  • Maleic Anhydride
  • Methanol
  • Methyl Bromide(Bromomethane)
  • Methyl Chloroform (1,1,1-Trichloroethane)
  • Methyl Ethyl Ketone (2-Butanone)
  • Methyl Isobutyl Ketone (Hexone)
  • Methyl Isocyanate
  • Methyl Methacrylate
  • Methyl Tert Butyl Ether
  • Methylchloride (Chloromethane) 
  • Methylene
  • Methylene chloride (Dichloromethane)
  • Methylene diphenyl diisocyante (MDI)
  • Naphthalene
  • Nitrobenzene
  • Pentachlorophenol
  • Phenol 
  • Phthalic Anhydride
  • Propylene Dichloride (1,2-Dichloropropane) 
  • Propylene Oxide
  • Styrene
  • Styrene Oxide
  • Toluene
  • Trichloroethylene
  • Triethylamine
  • Vinyl acetate
  • Vinyl Bromide
  • Vinyl Chloride
  • Vinylidene Chloride (1,1-Dichloroethylene)

To explore the possible health effects of these and other pollutants, please visit the following internet sites: