Blood samples were collected from members of 40 families in three generations. The families live in villages within a distance of 100 km from the nuclear weapons test site, in the area that received the heaviest radioactive fallout. The population in these villages was exposed to radiation doses that were in some cases even thousandfold compared with normal yearly background radiation. The control group consisted of 28 families living in clean, uncontaminated area.

The blood samples were used for minisatellite analysis which reveals genetic mutations in the offspring. Minisatellite mutations are not linked to malformations but they offer an excellent tool to examine the frequency of radiation-induced genetic changes at molecular level.

In 1949–1989 the Soviet Union performed altogether 470 nuclear weapons tests in Semipalatinsk, Kazakhstan. The most significant radiation exposure to people living in the Semipalatinsk area was caused by four nuclear weapons tests performed above ground. These tests were carried out in 1949–1956.

Until 1963 nuclear weapons tests were conducted both in the atmosphere and on the ground. In August 1963 a Test Ban Treaty was signed in Moscow that prohibits nuclear weapons tests in the atmosphere. Since then only underground tests were performed.

The study results show that radioactive fallout from nuclear weapons tests made above ground in the late 40s and early 50s nearly doubled the frequency of genetic mutations. The highest frequency of mutations occurred in those who were exposed to the heaviest radioactive fallout. When nuclear weapons tests in the atmosphere were stopped the fallout decreased and mutations became more infrequent. This indicates that the 1963 Moscow Test Ban Treaty prohibiting nuclear weapons tests in the atmosphere has been an effective action in reducing genetic risks from radiation.

The minisatellite analyses were performed by the research group of Dr Yuri Dubrova from the University of Leicester, U.K. Other collaborating parties of this study, which was funded by the European Union, were the Research Institute of the Kazakhstan Academy and the University of Warwick, U.K.

The STUK collaborators participating in this study were Research Director Sisko Salomaa, Head of Laboratory Riitta Mustonen and Senior Scientist Carita Lindholm from the Department of Research and Environmental Surveillance.

The results were published in the Science on February 8, 2002.