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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.