Skip to content

Environmental Protection Agency's Reference Concentrations (RfCs)

Environmental Protection Agency's Reference Concentrations (RfCs)

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:
The Environmental Protection Agency's Integrated Risk Information System - list of non-cancer and cancer risk values for many pollutants
The Agency for Toxic Substances and Disease Registry - list of pollutants and corresponding minimum risk levels
The National Institutes of Health, National Library of Medicine's Hazardous Substances Data Bank (HSDB)
The Environmental Protection Agency's Health Effects Notebook for Hazardous Air Pollutants
The Agency for Toxic Substances and Disease Registry's Frequently Asked Questions about contaminants found at Hazardous Waste Sites