It should be emphasized that the biological absorption, incorporation, and elimination of radioactive isotopes are closely correlated, with the chemical nature and state of the substance with which the isotope is com bined, the physical and chemical conditions of the medium in which the organism encounters the isotope, as well as with the constitutional proper ties of the organisms themselves.
These factors must be fully taken into account if we are to assess correctly the recently evolved concept of discrimination factors, and the raging debates on the extent of danger from global radioactive fallout, especially of following thermonuclear tests /28-33/.
It is clear that detailed, specific studies of radioecological processes cannot be an aim in themselves. However, whereas the general principles of radioecology may be readily implemented, each specific inquiry made by practical workers will require fairly detailed surveys of the actual local microbial ecology, or of the ecological aspects of the plant or animal populations, since these largely determine the accuracy and feasibility of the respective practical suggestions. This statement can be readily illus trated by several examples.
At present, we are faced with the acute problem of decontaminating large areas of arable land contaminated, in varying degrees, by radio active products with prolonged half-lives. Obviously, removal of conta minated topsoil (e. g., a layer approximately 5 cm thick) from large areas is not feasible. It was suggested, that the contaminated area be plowed under to a depth of 70 cm, thereby burying the contaminated topsoil /34/. It was claimed that this would prevent radiation, as well as scattering of the various radioisotopes by winds or their eluviation by rainwater. How ever, the principal aim was to prevent any contact between the assimilating root systems of the crops and the contaminated soil layer, thus preventing the undesirable build-up of radioisotopes in the plants, i. e, , in the food, fodder, and industrial products.
This suggestion would appear to be quite reasonable, although it would involve expensive work with powerful tractors and special plows. However, ecologists might still question the expediency and effectiveness of this method of decontaminating farmlands. Decontamination implies removal
and burial of radioactive isotopes, whereas here, the latter remain essentially in place in the soil volume, i. e., in the biosphere, in the body of a specific structure with its particular processes. Capillary forces, for example, raise the water together with its solutes to the upper soil horizon. It is known that certain dangerous radioisotopes are fairly hydro topic, and are only partially fixed by the soil in ion-exchange reactions.
In 1960 and 1961, at meetings of the Moscow Society for Natural Research we reported /64/ pronounced migrations of radioisotopes (Sr90. Ca45) together with the circulating capillary soil moisture (in loamy and sands). The isotopes rise with the moisture toward the evaporating soil surface, where they concentrate within a relatively short time in the topmost soil layer (0.5-mm thick). Furthermore, the root systems of some cultivated plants may penetrate to considerable depths, especially in nutrient-de ficient soils. Moreover, the widespread weeds with their deep-reaching roots will carry the buried isotopes from the bottom to the top soil horizons. This is further aggravated by the possible radioisotope migration from one species to another through their root systems. We have established /35/ that animals living in the soil contribute to the assimilation of radioisotopes by plants by spreading the elements not only by way of biological migration but also mechanically by burrowing in the soil, throwing the soil up from the deeper to the surface horizons, etc. As a result, radioisotopes with long half-lives, far from being buried for extended periods of time, might be expected to spread and continuously contaminate the upper and lower soil horizons, as well as the crops. Consequently, the method of primary deactivation described might prove unsatisfactory, necessitating repeated decontamination of the same area by different means. On the other hand deep plowing-under might prove effective in areas contaminated by iso topes with short half-lives. Within certain limits it might also prove safe in special circumstances, such as in soils devoid of plant cover and with a poor fauna. In any event, this method should be evaluated by long-term investigations and experiments.