1. Benzene extracts of some carbon blacks were found to contain 3,4-benzpyrene, a strong carcinogen for animals; 1,2-benzpyrene, a weak carcinogen; and five other related aromatic hydrocarbons: pyrene, fluoranthene, 1,12-benzperylene, anthanthrene, and coronene.

  2. These compounds possess peri-condensed ring systems in which carbon atoms are shared by three rings. They contain the smallest possible proportion of hydrogen to carbon for molecules of this type and size. A theory of their formation is presented.

  3. Furnace blacks, with an average particle diameter of 80 mµ or more, possessed all 7 of the aromatic hydrocarbons; those with particle size below 50 had few or none. A rough correlation existed between yield of extractable aromatic hydrocarbons and average particle diameter of the carbon blacks.

  4. These hydrocarbons were not detected in any channel blacks, which have small particle diameter averaging from 10 to 30 mµ, and are made by a different process.

  5. Based on these observations an interpretation of the apparently contradictory reports in the literature on the carcinogenicity of soot is possible. 3,4-Benzpyrene seems to be the principal carcinogenic agent. This hydrocarbon can be extracted from many soots with lipid solvents, and these extracts produce tumors in animals at the site of application. Soot itself appears to be carcinogenic on skin but possibly not on respiratory tract epithelium. It is suggested that this difference in behavior is explained by the presence of lipid solvent (the sebaceous secretions) in the skin and its absence in the respiratory tract.

  6. It is further suggested that the differences in extractable aromatic hydrocarbons from carbon blacks can be explained by the phenomenon of adsorption.


This work was supported by a research grant from the Committee on Growth acting for the American Cancer Society, and by an institutional grant from the American Cancer Society.

A preliminary report of this work was presented before the American Association for Cancer Research, April 27–29, 1951, and was published in abstract form in the Scientific Proceedings of that meeting.

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