In addition to such naturally occurring environmental carcinogens as ionizing radiation and ultraviolet light, there are thousands of manmade chemicals suspected of causing cancer in humans.

The petrochemical industry has invented a whole series of reactions that do not occur naturally in living things. These new chemicals are incompatible with living things substances to which human beings have never been exposed. There are at present over 250,000 chemicals in use in the American industry, many of them under suspicion of increasing cancer risk.

The induction of cancer in laboratory animals has been utilized to demonstrate the increased cancer risk of long-term industrial exposure to a number of chemicals. Among the high risk situations are: (1) bladder cancer among aniline dye workers that handle 2-naphthylamine and some related chemicals; (2) bone cancer among workers who inhale or ingest radium; (3) lung cancer among workers who inhale chromates; (4) radioactive ores, asbestos and iron; (5) cancer of the nasal sinuses and of the lung in nickel mine workers; (6) skin cancer among workers handling distillation and fractionation products of coal, oil, shale, lignite and petroleum.

The economic impact of cancer is difficult to assess since precise figures are not available, but researchers have estimated the total cost of cancer to the American economy as approximately $15 billion, 2 percent of the gross national product, at the current rate of inflation. However, the incidence of lung cancer is not confined to urban industrial areas but is distributed across all demographic areas, including rural populations.

Another variable that must be accounted for is the role of smoking in lung cancer. It is generally accepted in the literature that smoking plays a major role in the occurrence of lung cancer. The biological assay has demonstrated that there are at least 16 carcinogenic hydrocarbons in the mainstream of cigarette smoke.