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Electromagnetic radiation may be : Non-ionizing : has energy, can't produce ionization e.g. UV, IR. Ionizing : has energy, can produce ionization e.g. X-ray and α and β particles Sources of ionizing radiation : Radioisotopes : Unstable atomic nuclei emitting radiations e.g. U Fallout : It is the mixture of radioactive wastes that are released from nuclear processes into the atmosphere and gradually settle to the surface of the earth where it is inhaled or eaten with contaminated food. 235 Sources of exposure to ionizing radiation: External: Cosmic radiations contain α- particles, X-rays, gamma –radiation. Internal : inhalation or ingestion of radioactive isotopes e.g. Uranium. Soil : absorption from soil depends on chemical form. e.g. Sr90 is chemically similar to calcium, so absorbed by plants and is eaten. Biological effects of ionizing radiation: 1-Ionization of various molecules as well as water in the biological system resulting in the formation of reactive free radicals as superoxides which cause lipid peroxidation and finally cellular damage. 2-Mutation, which may lead to: - Autosomal abnormality ( Somatic ) cancer. - Genosomal Congenital malformation. Toxic symptoms of radiation : 1- Blood: count of leukocytes & blood platelets, hemorrhage and anemia. 2- Skin : lesions, dehydration , alopecia, ulceration & rashes. 3- CNS : headache, fever& amnesia. 4- GIT : loss of appetite, nausea, vomiting diarrhea& destruction of mucosa. 5- Cancer : Lung , thyroid & skin cancer. 6- Genetic damage: malformation & sterility (due to spermatogenesis & destruction of ova). 7- Eye: cataract. Chemical protection of radiation : Sulfhydryl compounds: e.g. cystine, cysteine, cysteamine, glutathione ( GSH), B- mercaptoethylamine ( MEA), 2-mercaptoethylguanidine (MEG). Mechanism: These compounds are effective in presence of O . They compete with O for organic free radical (R), allowing repair of the target molecule to occur. While the sulfhydryl ( P-SH) compounds suffer the damage. R+O2 Radiation RO2 damage of the cell & cell repair. R+ PSH RH + PS N.B.: this reaction occurs before O can react with R. 2 2 2 2- Certain alcohols : e.g. Dimethylsulfoxide ( DMS). It provides protection as it's a selective OH radical scavengers. Treatment of toxicity of radioactive agents: Examples: -Washing contaminated skin with detergents -Absorption of plutonium Pu239 through wounds is treated by I.V. Diethylene triamine pentaacetic acid ( DTPA ) which chelates Pu 239.