Some deposition occurred however in areas near to each city, owing to local rainfall occurring soon after the explosions. This happened at positions a few kilometres to the east of Nagasaki, and in areas to the west and north-west of Hiroshima. For the most part, however, these fission products were carried high into the upper atmosphere by the heat generated in the explosion itself. Unrecorded deaths of military personnel and foreign workers may have added considerably to these figures. From the estimated radiation levels, however, it is apparent that radiation alone would not have been enough cause death in most of those exposed beyond a kilometre of the ground zero below the bombs.
Most deaths appear to have been from the explosion rather than the radiation.
Teratogenic effects on foetuses was severe among those heavily exposed, resulting in birth deformities and stillbirths over the next 9 months. Beyond this, no genetic damage has been detected in survivors' children, despite careful and continuing investigation by a joint Japanese-US Foundation. There were two further, and smaller, sources of exposure. One, already mentioned, was due to the 'black rain' which fell in some areas, carrying down radioactive materials from within the rising cloud of fission products. The exposures due to these depositions are in general estimated to have been small, but some increased activity from the fission product radionuclide caesium-137 remained detectable for many years in soil and farm products in the Nishiyama district east of Nagasaki.