Wheat plants grown in soil from near the Chernobyl nuclear power plant have six times the rate of mutations as those grown in clean soil, according to a study in this week's issue of Nature.

This suggests that chronic exposure to radiation may cause more mutations than scientists thought, according to Olga Kovalchuk of Switzerland's Friedrich Meischer Institute, a co-author of the study. An accident at the Chernobyl nuclear power plant contaminated acres of land with nuclear fallout in 1986. She said the difference lies in long-term low levels of radiation versus short-term bursts of high levels. "In the past, scientists have estimated the effects of long-term exposure to radiation by (looking at) short term but higher intensity experiments," said David M. Hillis, director of biology at the University of Texas, Austin. Soils in Chernobyl, on the other hand, have been contaminated by low levels of radiation for almost 15 years. "Theoretically," Kovalchuk wrote, "this low level exposure should not cause such a large increase in the mutation rate." But now it seems that chronic exposure to low levels produces much higher levels of mutations than would be expected, she said. Kovalchuk and her colleagues said the study also raises questions about the genetic hazards of chronic radiation. The mutations they uncovered were found in the offspring of exposed plants. Kovalchuk says the next step for the project, a joint effort of both Swiss and Ukrainian scientists, is tosort out the influence of other environmental factors, like pollution and local environmental changes, on both wheat and barley grown in clean contaminated soils.