Fourteen years after the Chernobyl nuclear accident, crops grown in contaminated land surrounding the former power station show a mutation rate six times higher than normal, researchers now report in Nature1. Similar but controversial results have previously been seen in humans and rats.

Olga Kovalchuk from the Friedrich Miescher Institute, Basel, Switzerland, and colleagues investigated the effect of chronic radiation exposure on wheat plants. They compared identical populations planted in heavily contaminated land near Chernobyl and in clean soil roughly 30 kilometres away.

After just one plant generation -- ten months -- Kovalchuk's team saw an increased mutation rate in plant offspring. Each plant received relatively low radiation doses, which theoretically should not cause so many mutations. This suggests "that chronic exposure to ionizing radiation has effects that are as yet unknown," they say.

The researchers spotted the differences by looking at, and comparing, the same 13 tiny regions of the plants' genomes. This new genetic 'profiling' approach enabled them to spot unusual gains, deletions or repeats of genes.

It is possible that the differences noted by the group were caused by seed contamination or migration. But given that neither plot had previously contained wheat and that wheat is self-pollinating, these are not likely explanations for the genetic changes they observed.

The reactor explosion in the Chernobyl nuclear power plant in 1986 killed 31 people and released an estimated seven and a half tonnes of uranium dioxide into the surrounding countryside. More than one hundred thousand people were evacuated from a 30-kilometre radius of the plant.

It is estimated that five million people were exposed to radiation in the Ukraine, Belarus and Russia, but the exact genetic consequences of these effects is not yet clear. The World Health Organization says that, so far, there has been a large increase in thyroid cancer among children in the affected areas.

"Our findings raise the important issue of the genetic hazard of chronic radiation exposure to the germline," Kovalchuk's team point out. The 'germline' of an organism consists of the cells involved in reproduction, such as sperm and eggs in humans; these cells pass hereditary characteristics from generation to generation.