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Nuclear Tests, Fallout Boosted DNA Mutation Rates

Thu Feb 7, 5:29 PM ET

By Keith Mulvihill
NEW YORK (Reuters Health) - People who lived near a nuclear test site in the former Soviet Union during active above-ground and atmospheric testing have nearly twice as many inheritable DNA mutations as their countrymen and women who were not exposed to radiation, according to the results of a new study.

But once atomic testing was forced underground by a US-USSR treaty, the international team of researchers found, the mutation rate in later generations of test-site neighbors began to drop.

Dr. Yuri E. Dubrova of the University of Leicester, UK, and colleagues investigated the effects of nuclear testing at Semipalatinsk nuclear test site in Kazakhstan, formerly part of the Soviet Union and now an independent nation.

Between 1949 and 1989, 470 nuclear tests were performed at the Semipalatinsk site, some of which resulted in relatively high contamination of surrounding territories with radioactive fallout, Dubrova explained in an interview with Reuters Health.

The study "provides us with the first solid experimental evidence of an elevated mutation rate in the germline of families exposed to ionizing radiation," Dubrova said. "Germline" refers to the genes contained in a man's sperm and a woman's eggs, which are passed on to their children.

From 1949 to 1963, nuclear tests at Semipalatinsk took place in the atmosphere or on the ground, while tests after 1963 were conducted underground. Up to 85% of the radiation exposure to nearby residents came from four surface tests, conducted in 1949, 1951, 1953 and 1956.

The investigators evaluated the germline mutation rate in 40 three-generation families living near the nuclear test site, who were compared with 28 three-generation families from another rural region of Kazakhstan who had not been exposed to radiation.

The researchers divided the radiation-exposed families into two groups: those born before 1949, who had likely received the heaviest doses of radiation, and those born in 1950 and later. Individuals in the second group who were born between 1950 and 1956 were also exposed to a significant amount of radiation, while those born later were not.

People born before 1949 near Semipalatinsk had 1.8 times as many germline mutations as their counterparts who had not been exposed to radiation, Dubrova and colleagues found. Those born in 1950 and afterwards had 1.5 times the number of mutations seen in the unexposed group, according to the report in the February 8th issue of the journal Science.

"This means that exposure to ionizing radiation has resulted in (an) elevated mutation rate in the germline of the affected families," Dubrova told Reuters Health.

"The most interesting finding is that in the less-contaminated group, a negative correlation between germline mutation rate and the parental year of birth was found," he said. "This decrease in mutation rate perfectly reflects the improvement of the radiological situation in the area around the site after the cessation of atmospheric and ground nuclear tests in 1963."

According to Dubrova, the findings show that the Limited Test Ban Treaty, which banned atmospheric and above-ground nuclear tests and was signed by the US and USSR in August 1963, has been effective in reducing the genetic risks for the exposed population.

As far as health consequences due to the exposure, "an elevated incidence of cancer has been reported for this area, but these data are still preliminary," Dubrova stated.

"The message is straightforward," Dubrova said. "The testing (of nuclear weapons) in the atmosphere and above the ground was not the best idea, and the Soviet and American governments were clever enough to ban this testing in 1963."

SOURCE: Science 2002;295:1037.

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