Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.2.1
Japanese Atomic Bomb Survivors

1.2.1.3
In Utero Effects>

References

"Birth defects: children with small head size, mental retardation, and reduction in IQ scores and school performance were born to pregnant mothers exposed to high doses; there were threshold doses of ~50 and 10 cGy, respectively, for severe mental retardation and reduction of IQ scores and school performances.

"Small Head Size"

"The frequency of small head size among children exposed prenatally to atomic bomb radiation in Hiroshima increased with doses above 10-19 rad, whereas in Nagasaki an increased prevalence of small head size was found only among children exposed in utero to more than 150 rad of atomic bomb radiation. It should be noted that when exposure occurred later than 17 weeks after fertilization, the incidence of small head size was low even after high doses of radiation.

"Mental Retardation"

"The frequency of severe mental retardation after prenatal exposure to atomic bomb radiation at Hiroshima increased significantly with increasing doses above 50-99 rad, whereas in Nagasaki severe mental retardation occurred only at doses over 300 rad.

"When the IQ scores and school performances of prenatally exposed survivors of the Hiroshima atomic bomb were compared with those of suitable comparison groups, the period 8-15 weeks after fertilization was again the period of greatest vulnerability to mental injury after exposure to bomb radiation. The threshold dose for a reduction in either IQ or school performance, after exposure to radiation 8-15 weeks after fertilization, was estimated to be ~10 rad."