Epidemiological studies on disturbances of human fetal development in areas with various doses of natural background radiation. I. Relationship between incidences of Down's syndrome or visible malformation and gonad dose equivalent rate of natural background radiation.

The relationship between environmental radiation (mSv X a-1) to the gonads and incidences of Down's syndrome and visible malformation was analyzed using Kendall's rank correlation method. The subjects, studied during a 3-yr period (1979-1981), were inhabitants of 46 prefectures in Japan that had various dose rates (mu R/h) of natural background ionizing radiation. Results showed that the natural background very low-dose radiation rate was not a predominant factor responsible for inducing Down's syndrome or other visible malformations.