After 1990 a large number of studies have been conducted on the relationship between the concentration of radon in buildings and the incidence of lung cancer in the general population. Largest in scale were the studies conducted in Europe, North America and China. Based on this data the WHO reached the conclusion that in different countries between 3 and 14% of the cases of lung cancer were attributable to radioactive exposure due to radon.

Statistics in Bulgaria show that each year over 200 new cases of malignant neoplastic diseases of the respiratory organs and chest are detected per 100,000 population, and the annual death rate due to these causes is over 50/100,000. Consequently, between 6 and 28 per 100,000 of these annual new cases could be correlated to elevated concentrations of radon. Even though lung cancer is among the least frequently detected types of neoplastic diseases per capita, it takes second place with respect to lethality.

In 2005 the World Health Organization initiated the international project “Radon”, with the participation of experts from around 40 countries. One result of the project is the WHO Handbook on Indoor Radon: A Public Health Perspective, published in 2009. In this text the radiation burden to the population due to indoor radon is cited as the second most important cause of lung cancer after tobacco smoking, and the most important cause for non-smokers. In the United States alone, around 21,000 deaths from lung cancer annually can be attributed to this factor. Significant importance has been ascribed to the necessity for the creation of national radon programs with the following priorities:

– Reducing risks for the population as well as individual risk for people living in areas with high radon concentrations

– Establishing of a national reference value of 100 Bq.m-3 and, if that is not feasible, establishing national reference values not exceeding 300 Bq.m-3.

– The creation and implementation of rules and regulations, detailing anti-radon measures in new-build construction of dwellings

– The development of national guidelines for measurement of radon concentrations, ensuring the quality and consistency of results.

The National Programme aims to create and implement a long-term policy for the mitigation and prevention of hazards for the health of the Bulgarian population stemming from the effects of high radon concentration in buildings.