The low level of radiation that occurred after the accident at the Chernobyl nuclear power plant in 1986 did not appear to affect the mental performance of exposed children, researchers in Israel have found.

However, they observed that mothers who were pregnant at the time of the accident have children with above-average rates of hyperactivity, regardless of the level of radiation they were exposed to. The investigators therefore suggest that the hyperactivity may reflect heightened anxiety in mothers that was transferred to their offspring.

Studies of Japanese survivors of the atomic bombs during World War II showed that fetal exposure to high doses of radiation increased the risk of mental retardation and small head size. It was feared that prenatal and early childhood irradiation after the Chernobyl accident would have similar consequences, Dr. Gad Rennert and his team explain in the American Journal of Epidemiology.

Rennert, of the Carmel Medical Center in Haifa, and colleagues studied 1629 children who immigrated to Israel from the former Soviet Union. The children were either unborn or up to 4 years old at the time of the accident.

A total of 667 came from the highly exposed Gomel region, while 408 came from Mogilev and Kiev, which were only mildly exposed. The remaining 554 were from the non-exposed cities of Moscow and St. Petersburg.

There was no relation between exposure to radiation and measures of intelligence or of attention-deficit/hyperactivity disorder (ADHD), the researchers found. However, children of mothers who were pregnant at the time of the accident scored higher for ADHD, regardless of the exposure level.

“If you look at the accumulation of all the data, the only significant finding with regard to Chernobyl that repeats itself is the increase in thyroid cancer,” Rennert told Reuters Health. “Other than that, it seems as if there was no major influence of the accident” on people’s health.

“One thing we did see was this extreme degree of anxiousness among women who were pregnant at the time of accident,” he continued.

“It was similar in those who were only 50 km away from the site and in those who were hundreds of kilometers away. What we see is not any influence of the exposure itself but the influence of the trauma that people experienced,” he said.

The research is ongoing, Rennert noted. “We are closely following a cohort of more than 1000 individuals who were on clean-up teams. These were individuals who were put at the highest degree of risk. If they don’t show any consequences of that exposure to low-level radiation, nothing will ever be shown.”

SOURCE: American Journal of Epidemiology, September 2004.