Radiation toxicology

Radiation toxicology studies the distribution kinetics and biological effects of radioactive isotopes. This information is used for the establishment and evaluation of allowable levels of content and intake of radioactive isotopes in the body by air, water and food.
Exposure by ingestion of radioactive isotopes into the body continues uninterrupted until the isotope is completely disbursed or not will be removed from the body. Sometimes the exposure lasts for years or even throughout the life of the victim. When this occurs most often predominant exposure of certain organs and body systems.
The degree of toxicity and specific biological effects of the radioactive isotope is determined by its physical appearance and the radiation energy, half-life, the dose of the emitter), chemical (form input connections, solubility at pH tissues and organs, the degree of affinity of tissue structures and physiological (path receipts, value and speed of absorption of radionuclides from the depot, the nature and type of distribution, the rate of excretion of properties, and the degree of radiosensitivity of the studied object.
Biologically active number of most radioactive isotopes are insignificant weight. The number of Sr90, corresponding to 1 Curie, weighs 6,9·10-3 g, and maximum permissible dose (2 mccoury) is only 1.4·10-8 , Damaging action of radioactive isotopes is not called their chemical properties and radiation during decomposition. Only very slowly decaying radioactive isotopes (U238, Th232 and others) on the foreground there is no radiation and chemical toxicity. Radioactive isotopes can enter the body through the lungs (inhalation of aerosols, fumes, smoke), gastrointestinal tract (water and food), the skin and wounds. For diagnosis and therapy, in addition to the above, the use of subcutaneous, intramuscular, intraperitoneal and interstitial introduction of isotopes.
Inhalation of radioactive aerosols, passing through the respiratory tract, partly deposited in the nasopharynx and oral cavity and from there, it may be ingestion; certain size particles and gases get into the lungs. As a result of activity of ciliated epithelium is a certain amount of particles removed from the respiratory tract and also due to ingestion acts in the gastrointestinal tract.
The degree of penetration, the magnitude and duration of the delay of aerosols in the lungs depend on their charge particle size and properties inhalated connection. If inhaled poorly soluble compounds with optimal conditions for the delay of aerosols in the lungs (a particle size of >0,5≤2 MK), about 25% of the radioactive substance is immediately deleted from exhaled air, 50% is delayed in the upper respiratory tract and is removed for several hours as a result of activity of ciliated epithelium. 25% of aerosols released into the lower respiratory tract, 10% rather quickly, also thanks to the activity of ciliated epithelium, are removed from the lungs are in the mouth and swallowed.
The remaining 15% is slowly disappearing from the lungs. A large part of the remaining activity is retained in the lungs or phagocytized and into the lymph nodes, the lungs, where it is firmly attached. Because of this, and also a small amount of lymph nodes in comparison with the mass of lung poorly soluble concentration of radioactive aerosols in the lymph nodes in the late periods after inhalation of isotope can 100-1000 times higher than that of light. Well soluble compounds of radioactive substances rapidly absorbed from the lungs and depending on their properties, in different ways, distributed in the body. Absorption of radioactive isotopes from the gastrointestinal tract depends on the chemical properties of the input connection and the physiological state of the organism. With rare exceptions (tritium oxide) radioactive isotopes are poorly absorbed through intact skin.
Distribution in the body of isotopes of elements belonging to the same group of the periodic system, has a lot in common. The main elements of the I group (Li, Na, K, Rb, Cs) fully rezorbiruetsa from the intestines, relatively evenly distributed to organs, relatively rapidly excreted in the urine. The elements of group II (CA, Sr, BA, Ra) is well absorbed from the intestine, selectively deposited in the skeleton, a few more are excreted in the feces than with urine. The main elements of the III and IV of side groups, including light the lanthanides, actinide and transuranic elements are practically not absorbed from the gut, but getting one way or another in the blood, selectively deposited in the liver, and to a lesser extent in the skeleton. They are excreted predominantly in the feces. Items V and VI of major groups with the exception of polonium relatively well absorbed from the intestine and are excreted almost exclusively (up to 70-80%) with urine during the first day, so the authorities are deposited in a relatively small amount.
The reduction of radioactivity in organs occurs as a result of radioactive decay, the redistribution of isotopes in the body or out of it. These processes occur simultaneously and independently from each other.
Physical decay of radioactive isotopes (see) obeys an exponential law, which means a constant share of radioactive atoms decaying per unit of time. The period of time for which the initial radioactivity of the isotope is reduced by half is called the physical half-lives.
To describe the kinetics of removing isotope of organs and tissues and the organism as a whole are exponential or power-law model. In the first case, to calculate the amount of isotope, which is in the body, accept that the allocation of it goes with constant velocity, i.e. per unit of time is allocated a certain fraction available in the body of the isotope. The elimination of isotope is most often described by the sum of two or more Exhibitor. This suggests that organ or tissue into several factions isotope with different strength fabric structures and different rates of excretion.
In the power-law model, calculate the quantity of the detainee in the body of the isotope as a function of time elapsed from the moment of getting the isotope in the body. Describing this dependence mathematical equations are found experimentally for each isotope.

The rate of the elimination of radioactive substances from the body (or authority) describe the biological half-life, i.e. the time during which the radioactivity is reduced by half only due to excretion of the substance. The length of time during which the radioactivity in the body is reduced by half due to radioactive decay and the removal of substances from the body, called the effective half-life.
The toxicity of radioactive substances, usually appreciate the amount of radioactivity per unit weight of the animal (mccoury/g, mcurie/kg, and so on). Biological effect, however, easier to link to the absorbed dose in the tissues, organs and organism as a whole, measured in radas (see Doses of ionizing radiation). The value of dose in radas can be calculated from the data on the number of isotope per unit weight fabrics, knowledge schema its collapse, i.e. the type and energy of the radiation and effective half-life.
The clinical picture of defeat, due to well resorbed from the introduction of radionuclides (Sr89, Sr90, VA, Cs137, Ra226, N3), does not depend on the way of their exposure. In case of bad resorbed depo radioactive isotopes (Y91, Y90, Ce144, Pu239, Po210) defeat is largely determined by the way of introduction of the substance and is characterized by prevalence of pathological processes in the introduction of the isotope.
When injected radioactive isotopes, evenly distributed in the body, the clinical picture of the radiation damage is basically the same as when exposed to external sources of radiation. With the defeat caused by the ingress of radioactive isotopes, selectively postponed in the bone tissue and the liver, there are changes associated with the place of the impact of the emitter. In particular, characterized by the emergence of bone tumors, leukemia, cirrhosis and hepatic neoplasms.
Given that the biological effect trapped in the body of radioactive isotopes can be eliminated only after their removal from the body, and the possibility of accelerating this process is still very limited, essential prevention of poisoning with radioactive isotopes (see Radiation hygiene). Therapy lesions caused by radioactive isotopes, is limited to measures that reduce their absorption from the gastrointestinal tract, the acceleration of removing them from the body by using various agents and treatment of intoxication.