Mental Retardation Following<i>In Utero</i>Exposure to the Atomic Bombs of Hiroshima and Nagasaki

Abstract

The prevalence of mental retardation in children tested at 17 years of age who had been exposed in utero to the atomic bombs of Hiroshima and Nagasaki was studied in relation to the most recent estimate of radiation dose received. Significant increases at doses greater than 50 rads in Hiroshima and 200 in Nagasaki were found, with the risk of mental retardation generally rising directly with increasing dose. The lower dose-effect in Hiroshima may have been due to irradiation by neutrons which were virtually absent in Nagasaki.