Cancer incidence and geochemical factors in the environment.

Between 1961 and 1987, 9875 cases of cancer were registered in the district of Zdar nad Sazavou in southern Czechoslovakia; this district covers an area of 1627 km2 and has a population of 125,000 living within 197 identifiable communities. The age-standardized cancer incidence (standardized incidence rate, SIR) for selected cancers was calculated for each of the 197 communities. Five distinct geological areas were identified in the district; the percentages of the communities with a high incidence of cancer in each of these five areas were compared and statistically tested. More than 95% of the communities with a significantly high incidence of cancers of the digestive organs, lymphomas, leukaemias and all childhood cancers were situated in the areas containing tectonic faults or geological substrata which allowed radioactive elements (such as U, Rn, Co and Th) and heavy metals (for example, Pb, Zn, Cu and Cd) to intrude to the surface. Important quantities of heavy metals and radioactivity were found in drinking water, air (fall-out, including dust) and aerosols. The role of geochemical factors in the environment as possible causes of the high incidence of some cancers is discussed.