ECOLOGICAL BIOCHEMISTRY - Study Guide - V. M. Isaenko 2005

Chapter 9. RADIORESISTANCE OF ORGANISMS

Among the numerous environmental factors that have continuously influenced organisms throughout the course of evolution, ionizing radiation occupies a prominent place. It encompasses corpuscular radiation (consisting of elementary particles such as electrons, positrons, neutrons, protons, mesons, and others, as well as atomic nuclei of various elements) and electromagnetic radiation (ultraviolet, X-rays, and gamma rays). The interaction of this radiation with the medium—both directly and indirectly—leads to The ionization of atoms and molecules, resulting in The formation of electrically charged particles of opposite signs. The phenomenon of atomic and molecular ionization occurs because ionizing radiation transfers an amount of energy to the electrons of outer orbitals that exceeds their binding energy to the atom or molecule, thereby causing the ejection of an orbital electron.

Since the dawn of life on Earth (approximately 4.5 billion years ago), organisms have been exposed to ionizing radiation. Its high initial intensity was driven by the decay of radioactive chemical elements in the Earth's crust (derived from the Latin radiare, meaning to emit rays, and activus, meaning active) and the influx of significant cosmic radiation reaching the Earth's surface. However, over time—following the completion of the pre-biological stage of biochemical evolution—the Background radiation declined significantly due to the radioactive decay of elements, the attenuation of cosmic radiation at the Earth's surface, and the Formation of the atmosphere. Living organisms adapted to radiation levels that do not disrupt their vital Functions. This likely explains why any elevation of ionizing radiation above the natural background level is detrimental to living systems.

With the discovery of ionizing X-rays in 1895 and the phenomenon of radioactivity in 1896, anthropogenic enhancement of ionizing radiation levels began. The primary sources include radioactive fallout from the testing and deployment of nuclear and thermonuclear weapons; industrial nuclear explosions; the construction and operation of nuclear power reactors; uranium mining for nuclear fuel, its enrichment, and the Processing of nuclear waste; the application of ionizing radiation sources in medicine and industry; The production of electrical and electronic household appliances and consumer goods capable of emitting radiation; the extraction and utilization of fossil deposits with elevated concentrations of radioactive elements, particularly coal and mineral fertilizers; and scientific research. Environmental contamination by radioactive compounds poses a severe hazard, particularly As a result of radiation accidents at nuclear power facilities.

All of this underscores the critical importance of determining the sensitivity of living organisms to ionizing radiation and evaluating their capacity for radioadaptation. In-depth research in this area enables long-term ecological forecasting regarding the state of the biota under elevated levels of ionizing radiation, as well as The Development of protective measures and the search for radioprotective substances.

As previously noted, ionizing radiation also includes solar ultraviolet radiation with wavelengths below 300 nm. Only a significantly attenuated flux of this radiation reaches the Earth's surface, as the greater part of it is absorbed by the ozone layer located at an altitude of 20–25 km. Ozone (O₃) is formed from oxygen (O₂) through a photochemical reaction driven by the absorption of ultraviolet radiation.

Besides ionizing radiation, numerous Other types of radiation affect living organisms without inducing ionization. These include visible light (with wavelengths of 400–800 nm), infrared radiation (800 nm – 600 µm), and radio waves (600 µm – 3 • 10³ cm). All of these share an electromagnetic nature.