Michio Aoyama

Pre-Fukushima Radioactivity of the Environment

In the pre-Fukushima era, the greatest source of anthropogenic radionuclides in the global environment was coming from atmospheric nuclear explosions conducted during the period of 1945–1980. The nuclear bomb-derived radionuclides were primarily injected into the upper atmosphere, transported according to air motion, and, finally, deposited on the land and ocean surface. The Chernobyl accident in 1986, being another marked source of anthropogenic radionuclides in the environment, contaminated wide areas of Russia, Ukraine and European countries. The anthropogenic radionuclides released in the environment were transported into the ocean as a major sink. The radionuclides in the ocean move according to the physical and biogeochemical processes.

Estimation of Radiation Doses

Radiation doses to the Japanese population from inhalation of contaminated air, external irradiation, terrestrial and marine food contamination are estimated and compared with other sources of anthropogenic (global fallout, Chernobyl accident), natural (radionuclides in food, cosmic radiation) and medical applications (X-ray tests, CT-tests, etc.) of ionizing radiation. The estimated doses from inhalation, ingestion of terrestrial and marine food, and radiation exposure from radioactive clouds and deposited radionuclides were generally below the levels which could cause health damage of the Japanese population, as well as of the world population. The estimated total radiation doses to fish and shellfish in coastal waters during the largest radionuclide releases were by a factor of 10 lower than the baseline safe level postulated for the marine organisms, therefore no harmful effects are expected for the marine ecosystem as well.