INFLUENCE OF BUILDING TYPE AND YEAR OF CONSTRUCTION ON INDOOR RADON CONCENTRATIONS IN PERNIK CITY, BULGARIA

Radon (222Rn) is a radioactive gas and formed as a results of the radioactive decay of radium. Radon relieved from ground could accumulate in the building and contribute to human exposure. Radon is recognized as a carcinogenic agent by the World Health Organization and is the second leading cause of lung cancer after tobacco smoke. Radon in buildings is considered to be the most important indoor air pollutant, with harmful effects on the health of the population. The purpose of this survey is to analyze the influence of building type and year of construction on indoor radon concentrations in Pernik city, Bulgaria. The measurements of the indoor radon concentration in buildings located in the town of Pernik (housing, schools and kindergartens) from national database is used. The results for annual radon concentration in 70 dwellings, in 28 public schools and in 34 kindergartens is applied. The nuclear track detectors (CR-39) were used for measurements. The annual radon concentration in schools and kindergartens was evaluated using the seasonal factor for Pernik district. The descriptive statistic is presented according to type of building and year of construction in the article. The arithmetic means of radon concentrations are: for dwellings AM = 133 Bq/m3, for schools AM = 123 Bq/m3 and for kindergartens AM = 136 Bq/m3. The group of buildings built during the period 1950 – 1969 has the highest average value of indoor radon concentration (AM=152 Bq/m3). In order to evaluate the difference between of the radon concentration in the groups separated by type of buildings and year of construction the Kruskal Wallis test was applied. No statistically significant difference was found between the types of buildings, unlike between the groups on years of construction. The influence of year of construction on the radon level was analyzed by applying the discriminative analysis. The results shown that 7.2% of the radon variation could be explain by year of construction of the building