Occurrence of carcinogens in the external environment: epidemiological investigations

The variation in cancer incidence between European populations indicates that at least 50% of the cancer incidence in Denmark may be attributable to environmental factors, including factors related to living conditions and lifestyle, and, hence, in principle are avoidable. Based on data from epidemiological studies of cancer causes, it is estimated that 30-40% of the total cancer burden in Denmark could be prevented by application of already available knowledge. Epidemiological studies of cancer occurrence in relation to arsenic in drinking-water, chlorination of drinking-water, nitrates in drinking-water and ambient air pollution are briefly reviewed. Although the causal associations between these factors and cancer in humans are hypothetical and unproven, the available data allow a rough calculation of the maximum proportion of cancer cases which possibly can be caused by these factors. At most, a few percent of the total cancer incidence is attributable to these external environmental factors.