The "unexpectedly high" mutation rate, discovered by using DNA fingerprinting techniques, means that a significant proportion of the world's population doing jobs where even low-level radiation is present are exposing their unborn children to increased risk, the researchers say.

This will be of serious concern to the nuclear industry, which has repeatedly rejected claims that exposure to radiation among its workers can affect children yet to be conceived. The theory was put forward by a team at Southampton University as the reason for the leukemia cluster at Sellafield, but later rejected.

The new findings show that the radiation from the stricken Ukrainian reactor affected the sperm of fathers, leading to mutation in the DNA of the children. None of them showed physical deformities, because the DNA changes were slight, but the long-term effects are not known.

Three teams of scientists, from the Institute of Evolution and the Kupat Holim National Cancer Control Center, both in Haifa, Israel, and the Research Center for Radiation Medicine in Ukraine tested children of parents involved in the Chernobyl accident.

Families in which one child was conceived before the accident and one later were tested, along with control groups from areas with no radiation exposure. The increases in mutation rates as a result of the parents being exposed to ionizing radiation was "highly significant", the paper says.

The changes may cause increased risk of cancers or genetic instability in future generations. One hopeful finding was that the mutation rate in children conceived long after their fathers' exposure was reduced the longer the fathers had been in a radiation-free environment.

The researchers say that lower doses of radiation also produce mutations, suggesting that low level occupational or medical exposure to radiation could double the mutation rate in offspring.

This finding "needs serious attention," the researchers say.

"This is all the more important when a significant proportion of the human population is subjected to mutagenic pressure, due to medical diagnostics, industrial accidents, occupation or growth in environmental contamination."

© Guardian Newspapers Limited 2001

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