![]() ![]() In terrestrial ecosystems, soil corresponds to the major receiving pool of emitted radionuclides. The adverse effects are in correlation with the quantity of absorbed energy, the penetrating power of the radiation, the duration of the exposure, as well as with the reproduction rate of the cells of a certain tissue. Even though the radioactive contamination of the environment is relatively rare, it requires a great attention because of extreme degrading effects of ionizing radiation on living tissues. Since the middle of the last century, the radioactive contamination have appeared through the discharge of man-made radionuclides, making the ionizing radiation one of the important ecological factors, in line with other types of soil degradation (physical, chemical, and biological). On the other hand, anthropogenic activities, related to the development of nuclear energy and its versatile use, have become important source of pollution. The origin of NORM is related to the formation of the planet thus, their presence cannot be referred to as contamination. The term radioactive contamination indicates the unintended or undesirable presence of radioactive substances on the surfaces or within solids, liquids, gases, or biota. The world average values for soil activity coming from 226Ra, 232Th, and 40K are 32 Bq/kg, 45 Bq/kg, and 420 Bq/kg, respectively. The most important terrestrial radionuclides are 238U and 232Th decay series, as well as 40K. On the other hand, the rocks, minerals, and consequently the soil, contain naturally occurring radioactive materials (NORM), characterized by a long half-life periods. The 3H, 7,10Be, 14C, 26Al, and 39Ar are the main radionuclides produced after the interaction of atmospheric gases with cosmic rays. Some radionuclides occur naturally in the environment, and their presence is either cosmogenic or terrestrial. ![]() ![]() Since the half-lives of various nuclei vary from seconds to billions of years, the time required for their total decay significantly differ as well. The activity of a particular radioactive substance is characterized by the constant decay rate and the half-life (t 1/2-time taken for the activity of a given quantity of a radioactive substance to decay to half of its initial value), and it is a general rule of thumb that ten half-lives are required for each radioisotope to be eliminated. Radioactivity is a phenomenon related to unstable atomic nuclei with excess of energy and/or mass, which spontaneously decompose emitting ionizing radiation in the form of electromagnetic waves (gamma rays) or streams of subatomic (alpha, beta, or neutron) particles. Furthermore, the improvement and standardization of the methods for radionuclide speciation are necessary to enable comparison between studies and monitoring of the effects achieved by the soil treatments. The optimization of factors in control of chemical leaching methods, selection of cost-effective immobilization agents, especially among suitable wastes and by-products, and verification of long-term effects of remediating actions are the major challenges for future investigation in this field. When the excavation and off-site leaching treatments are uneconomic, impractical, or unnecessary, in situ stabilization by the addition of appropriate reactive materials is an alternative approach. Attention was focused onto remediation methods based on radioactive pollutants redistribution, for enhanced separation (chemical extraction) or containment (in situ immobilization). This chapter aims to highlight the importance of evaluating radionuclide distribution, for the selection of proper in situ or ex situ remediation strategy. Understanding the radionuclide distribution, mobility and bioavailability, as well as the changes caused by the variation of environmental conditions, is essential for soil rehabilitation. Accidental releases, nuclear weapons testing, and inadequate practices of radioactive waste disposal are the principal human activities responsible for radioactive contamination as a new and global form of soil degradation.
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