In modern cancer research the confirmation of a finding is rarely so belated, and practical preventive action can be swift. For vinyl chloride, a chemical used in aerosol sprays and in the manufacture of plastics, epidemiological and laboratory evidence accumulated quickly and simultaneously. In May 1970, Dr.P.L.Viola, a cancer researcher in Rome, reported that he had developed cancer in animals by using very high doses of the substance but concluded that the levels encountered in industry presented no danger to workers. Nevertheless, less than two years later American and European chemical manufacturers started both animal tests and epidemiological studies of vinyl chloride.

The first breakthrough came in Italy. In January 1973, Dr.Cesare Maltoni of Bologna found liver cancers in animals exposed to low levels of the chemical; his experiments were repeated and confirmed by Dr.Viola. Then in late 1973 and early 1974, three cases of a rare liver cancer turned up at a vinyl chloride plant in Louisville,Kentucky. An epidemiological search of the death records of workers at other plants showed that the same cancer, often misdiagnosed had struck again and again. Only a few weeks later, Dr.Maltoni brought in the final damning evidence; he had induced the cancer in his experimental animals, using dosage levels no higher than those faced by the workers in the plants.

As one historian of the episode commented, 'people hardly needed any more convincing then'. In 1973 and 1974, beginning even before the last pieces of the puzzle had been fitted into place, the use of vinyl chloride in aerosols, which could harm the general public was banned and plastics manufacturers reformed their procedures to bring the chemical down to safe levels within their plants.

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