SEVERE RADIATION ACCIDENTS AND THE ENVIRONMENT

摘要

In severe radiation accidents with releases of radionuclides into the environ-ment, high enough radiation doses are formed to potentially cause direct radiation injury of natural ecosystems. The dose fields characterizing the irradiation of plants, animals and humans in radioactive contamination of the environment are highly heterogeneous, and irradiation of natural objects per se has features such as non-equidosal effects. In other words, humans and various objects in the natural environment can receive different absorbed doses for an equal density of radioactive fallout. In this case, maximal doses in different representatives of nature (e.g. coniferous trees and some groups of animal populations such as those inhabiting forest litter or bottom sediments) can be 10-100 times higher than those in humans. Natural and artificial ecosystems and their main components are characterized by great differences in radiosensitivity. The total effect of these two factors - namely, heterogeneity of the dose field and non-equidosal pattern of irradiation, on the one hand, and differences in radiosensitivity, on the other - predetermines considerable differences in the degree of radiation injuries in ecosystems of various kinds. In the radiation accidents in the southern Urals (1957) and at Chernobyl (1986), coniferous forests proved to be in fact the only natural ecosystems where radiation injury manifestations were notable at the ecosystem level in large areas. Evident symptoms of radiation injury, up to lethality, were found in small areas of deciduous forests, as well as in mammals. Mesofauna of forest litters and benthic organisms inhabiting the water ecosystems proved to be radioecologically hot sites. The minimal injurious dose of chronic irradiation at the levels of ecosystems and populations of living organisms is 5 Sv/a. In representatives of animal populations in the zone of the Chernobyl accident, radiation injury of the thyroid caused by accumulation of iodine radionuclides proved to be of considerable pathological significance. For the processes of radiation effects in accidental radioactive contamination of lands, two (or three) periods are characteristic - the phase of acute radiation injury with possible manifestations of radiation injury is followed by the phase of post-radiation recovery [1].