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Several studies have shown an increased lung cancer mortality among Swedish metal and iron ore miners, as probably caused by exposure to radon and its daughters. An earlier study of zinc-lead miners has been updated. The results show a 16-fold increase in lung cancer mortality. Surprisingly, nonsmokers were more apt to develop lung cancer than smokers, but the induction-latency time was about nine years shorter on the average for the smokers. An explanation for these findings might be that smoking increases the thickness of the mucus layer and therefore protects the bronchial epithelium from alpha radiation, but it also promotes the development of cancer once induced by the radiation.

An earlier cohort study of Swedish railroad workers indicated a possible relationship between exposure to herbicides and an increased overall tumor morbidity and mortality. The cohort of 348 individuals has now been followed through October 1978. In this updated analysis of the causes of death among railroad workers, the observed number of tumor deaths was higher than expected, especially among individuals exposed in the earlier years of the study to both amitrol and phenoxy acids. However, the excess tumor mortality among persons exposed to amitrol became more moderate, and the earlier, slightly increased tumor mortality among people exposed to phenoxy acids more pronounced. No specific type of tumor predominated although there were three stomach cancers and three lung cancers. The result of the previous analysis of deaths among these railroad workers has been confirmed as to an excess of tumors, but the aspects of causal relationships to specific agents remain rather unclear, especially since workers exposed to a combination of amitrol and phenoxy acids seem to be the most seriously affected. However, the result, being in agreement with animal data and other epidemiologic studies, suggests a need for the careful handling of amitrol and phenoxy acids as increasingly suspicious carcinogens.