Feasibility study for a long-term follow-up in a historical cohort of Brazilian coal miners

The first Brazilian historical mortality cohort study on miners was conducted. The cohort consisted of 3224 workers in the underground coal mining industry in southern Brazil. This industry has been operating since 1942 without compliance with any regulatory standards, since there were no relevant national regulations. Over almost 60 years, about 5000 workers were exposed to high levels of radiation. However, later radiation exposure was significantly reduced, particularly that due to radon exposure. Recent radon concentration measurements indicated an average annual exposure to radon progeny of 2.1 WLM, ranging from 0.2 to 7.2 WLM. As radon exposure in the past was unknown, it can be suggested that mine workers have not been working safely as regards the health hazard related to radon and radon progeny exposure. The cohort inclusion criteria are as follows: (a) all male employees who had worked for at least one year at the coal mine; (b) workers with complete workplace information (underground and surface); (c) employment hiring between 1945 and 1997 and (d) the worker must have been alive on 1 January 1979. Through multiple strategies of search it was possible to follow up the members of the cohort with a success rate of 92%. This paper presents the characteristics of the study population and provides information about the feasibility of conducting a retrospective mortality study in Brazil, taking into account the methodological and logistical difficulties of conducting such a study in a developing country.