Occupation Aaron Blair, Ph.D.*	Industrial workers have long served as sentinels for the general population with regard to environmental hazards. Although many chemicals found in the industrial setting can also be found in the environment, industrial workers often have more intense and prolonged exposures to chemicals than does the general population. Consequently, cancers in humans caused by these substances are often first noted in the workplace. Many of the well-established and suspected chemical carcinogens were identified through occupational studies. One of the earliest examples occurred more than 200 years ago when, in 1775, Percivall Pott, a London surgeon, described a high frequency of cancer of the scrotum among chimney sweeps, a disease known at the time as "soot-wart." A century later, other scientists noted similar cancers among gas plant workers in Germany and among oil shale workers in Scotland. Some 40 years later, certain constituents of tar, soot, and oils, known as polycyclic aromatic hydrocarbons, were found to cause cancer in laboratory animals, thus identifying the specific substances causing cancer among workers in these occupations. Preventive action was taken in Denmark, where the chimney sweeps' guild, spurred by Pott's report, urged its members to take daily baths. The success of this action was noted in a report in the 1892 British Medical Journal, "Why Foreign Sweeps Do Not Suffer From Scrotal Cancer," which pointed out that the sweeps of Northern Europe seemed to benefit from this hygiene measure, but English sweeps, who apparently ignored such recommendations, continued to develop cancer. This brief detective story became the model for many later investigations of workplace carcinogens, including: observation of unusual cancers, or a high incidence of common cancers, among groups of workers; searches for responsible agents; demonstrations that the agent can cause cancer in laboratory animals; and, finally, implementation of preventive programs. Studies of occupational groups remain an important component of the current effort to identify the causes of human cancer. A listing and summary of evidence regarding occupational factors that may cause human cancer can be found in a series of critical monographs published by the International Agency for Research on Cancer (IARC). Since 1971, the IARC, an agency of the World Health Organization headquartered in Lyon, France, has published more than 60 volumes dealing with cancer risks from individual chemicals, and mixtures of chemicals, in selected occupations or industries. Individual exposures are reconsidered whenever indicated by new information. The most recent summary of all pertinent reviews was published in 1987 (IARC, Supplement 7).
continue

* From the Occupational Studies Section, Division of Cancer Etiology, National Cancer Institute, Bethesda, Maryland