Lung cancer and indoor radon exposure in the north of Portugal – An ecological study
Introduction
Radon is considered, by the World Health Organization, as a carcinogen and perhaps one of the greatest public health threat conveyed by indoor air. Among the factors identified as enhancers of lung cancer, radon is presently recognized as the second leading cause after tobacco [1]. Lung cancer is one of the most frequent and more lethal tumours in western countries. In Europe, lung cancer is the leading cause of cancer death [2]. Approximately 90% of lung cancers occur among smokers [3]. The effect of radon exposure is higher for non-smokers than for smokers, but the absolute risk is expected to be higher for smokers than for non-smokers given the higher lung cancer rate among smokers [4], [5], [6], [7].
Many studies have been conducted in USA, Europe and Asia to estimate the number of cases of lung cancer associated with chronic exposure to radon. The results confirmed that radon in homes contributes substantially to the occurrence of lung cancer. According to European Environmental Agency, exposure to radon is one of the best documented leading cause of cancer associated with environmental factors [8].
Radon is a noble gas originated in rocks and soils rich in uranium and is ubiquitous in the Portuguese territory [9], [10], [11]. The north region presents high district means concentrations, justified by the lithological constitution of most of the region. In Portugal radon is the main responsible (56.7%) of exposure to external radiation, being this exposure due to internal deposition and alpha irradiation of radon progeny [12]. The exposition occurs mainly indoors and radon concentrations depend on different factors such as soil composition, climate conditions, construction characteristics, inhabitants’ habits and type of ventilation [13]. The gas liberated by soil and rocks become a health risk if exhaled in large quantities and if is able to penetrate indoors [14], [15].
In Portugal, indoor radon exposure has not been considered a relevant public health problem as in many developed countries, either by health authorities or by researchers. Scientific studies concerning radon were mainly directed for the evaluation of radon concentrations and its conditioning factors [16], [17], [18].
The aim of this study was to assess the risk of lung cancer and estimate, for the northern region of Portugal, the number of lung cancer deaths, between 1995 and 2004, attributable to indoor radon exposure.
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Materials and methods
Regardless of health effects, the process of risk assessment on human exposure to air pollutants is generally similar. This process was originally defined by a committee of the National Research Council in 1983 and involves the application of four steps [3], [19]: identification of the potential health hazard and the population at risk, selection of the exposure-response relation, exposure assessment and risk characterization.
Results
Depending on the model applied (EAD or EAC) and the method used to account for the smoking habit (method 1 or 2), assuming a submultiplicative effect of radon and smoking, from 18 to 28% of lung cancer deaths could be associated with indoor radon exposure (Table 2). The model EAD with method 2 produced the fewest attributable deaths, the model EAC with method 1 the most.
Table 3, Table 4 provide a detailed analysis of the number of lung cancer deaths considering, respectively, method 1 and
Discussion
This is the first known published study developed on lung cancer mortality attributed to indoor radon exposure in Portugal and focuses on the resident population in the northern region. The number of deaths attributable to exposure to this indoor air pollutant was estimated based on lung cancer mortality registered and the results from the indoor radon measurement campaign developed in the decades 80 and 90 across the country.
Two different models proposed by the BEIR VI Committee [6] were
Conflict of interest statement
The authors declare that they have no conflict of interests.
Acknowledgment
We gratefully acknowledge to Eng. Gabriela Rodrigues for her help in the use of the Geographical Information System.
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