A Group B2 is Compounds for which animal data are sufficient to demonstrate a cause-and-effect relationship between Exposure and cancer incidence (rate of occurrence) in animals, and human data are inadequate or absent. In the national-scale assessment, the 15 air toxics classified as probable (B2) human carcinogens are: acetaldehyde, carbon tetrachloride, chloroform, 1,3-dichloropropene, ethylene dibromide, ethylene dichloride, hexachlorobenzene (HCB), hydrazine, lead compounds, methylene chloride, PCBs, polycyclic organic matter (POM), perchloroethylene, propylene dichloride, trichloroethylene.
Group C (possible human carcinogen): Compounds for which animal data are suggestive to demonstrate a cause-and-effect relationship between exposure and cancer incidence (rate of occurrence) in animals. In the national-scale assessment, the 4 air toxics classified as possible human carcinogens are: acrolein, mercury compounds, quinoline and 1,1,2,2-tetrachloroethane. Because unit risk estimates have not been developed for acrolein and mercury compounds, EPA has not estimated cancer risk for these pollutants.
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