Biological effects of radiation

Biological effects of radiation

• 1.
  BIOLOGICAL EFFECTS OFRADIATION: DEFINITION: The harmful effects caused to human beings and other living beings due to their exposure to radiation is called as biological effects of radiation.  Biological effects of radiation on living cells may result in three outcomes: (1) injured or damaged cells repair themselves, resulting in no residual damage (2) cells die, much like millions of body cells do every day, being replaced through normal biological processes; or (3) cells incorrectly repair themselves resulting in a biophysical change.  High radiation doses tend to kill cells, while low doses tend to damage or alter the genetic code (DNA) of irradiated cells. High doses can kill so many cells that tissues and organs are damaged immediately. This in turn may cause a rapid body response often called Acute Radiation Syndrome.  low doses – less than 10,000 mrem (100 mSv) – spread out over long periods of time (years) don't cause an immediate problem to any body organ. The effects of low doses of radiation occurs after many years. EFFECTS OF RADIATION ON CELLS • Biological effect begins with the ionization of atoms. The mechanism by which radiation causes damage to human tissue, or any other material, is by ionization of atoms in the material. Ionizing radiation absorbed by human tissue has enough energy to remove electrons from the atoms that make up molecules of the tissue. • The following are possible effects of radiation on cells: • Cells are undamaged by the dose • Ionization may form chemically active substances which in some cases alter the structure of the cells. These alterations may be the same as those changes that occur naturally in the cell and may have no negative effect. • Cells are damaged, repair the damage and operate normally • Some ionizing events produce substances not normally found in the cell. These can lead to a breakdown of the cell structure and its components. Cells can repair the damage if it is limited. Even damage to the chromosomes is usually repaired. • Cells are damaged, repair the damage and operate abnormally
• 2.
  • If adamaged cell needs to perform a function before it has had time to repair itself, it will either be unable to perform the repair function or perform the function incorrectly or incompletely. The result may be cells that cannot perform their normal functions or that now are damaging to other cells. These altered cells may be unable to reproduce themselves or may reproduce at an uncontrolled rate. Such cells can be the underlying causes of cancers. . ACUTE RADIATION DOSE, ACUTE DOSE: • An acute radiation dose is defined as a large dose (10 rad or greater, to the whole body) delivered during a short period of time (on the order of a few days at the most). If large enough, it may result in effects which are observable within a period of hours to weeks. • Acute doses can cause a pattern of clearly identifiable symptoms (syndromes). These conditions are referred to in general as Acute Radiation Syndrome. Radiation sickness symptoms are apparent following acute doses >100 rad. Acute whole body doses of >450 rad may result in a statistical expectation that 50% of the population exposed will die within 60 days without medical attention. Stages in acute radiation syndrome: • Prodrome - initial sickness • Latent stage – temporary recovery (feel better) • Manifest illness stage - symptoms depend on dose •Recovery or Death. • Blood forming organ (Bone marrow) syndrome(>100 rad) is characterized by damage to cells that divide at the most rapid pace (such as bone marrow, the spleen and lymphatic tissue). Symptoms include internal bleeding,vomiting, diarrhea, fatigue, bacterial infections, and fever. Recovery in 2 to 4 weeks…May last up to 6 months. Mild symptoms appear within a few hours and last for several days in prodromal stage. Latent Period: May last up to 4 weeks. Possible death due to infection, dehydration or hemorrhage. • Gastrointestinal tract syndrome (>1000 rad) is characterized by damage to cells that divide less rapidly (such as the linings of the stomach and intestines). Symptoms include nausea, vomiting, diarrhea, dehydration, electrolytic imbalance, loss of digestion ability, bleeding ulcers, and the symptoms of blood forming organ syndrome.
• 3.
  Latent Period: Lasts3-5 days. Death within 4 to 10 days after exposure primarily due to intestinal cell damage and also damage to blood-forming tissue results in hemorrhaging and dehydration. • Central nervous system syndrome (>5000 rad) is characterized by damage to cells that do not reproduce such as nerve cells. Symptoms include loss of coordination, confusion, coma, convulsions, shock, and the symptoms of the blood forming organ and gastrointestinal tract syndromes. Latent Period: May last up to 12 hours, or not at all.Death always within a few days of exposure due to increased fluid in brain (pressure). Death occurs before hematologic and gastrointestinal symptoms appear. Other effects from an acute dose include: • 200 to 300 rad to the skin can result in the reddening of the skin (erythema), similar to a mild sunburn and may result in hair loss due to damage to hair follicles. • 125 to 200 rad to the ovaries can result in prolonged or permanent suppression of menstruation in about fifty percent (50%) of women. • 600 rad to the ovaries or testicles can result in permanent sterilization. • 50 rad to the thyroid gland can result in benign (non-cancerous) tumors. CHRONIC RADIATION DOSE • A chronic dose is a relatively small amount of radiation received over a long period of time. The body is better equipped to tolerate a chronic dose than an acute dose. The body has time to repair damage because a smaller percentage of the cells need repair at any given time. The body also has time to replace dead or non-functioning cells with new, healthy cells. This is the type of dose received as occupational exposure. Somatic Vs Genetic Effects • Somatic effects appear in the exposed person. Somatic effects may be divided into two classes based on the rate at which the dose was received. – Prompt somatic effects are those that occur soon after an acute dose (typically 10 rad or greater to the whole body in a short period of time). One example of a prompt effect is the temporary hair loss which occurs about three weeks after a dose of 400 rad to the scalp. New hair is expected to grow within two months after the dose, although the color and texture may be different.
• 4.
  – Delayed somaticeffects are those that may occur years after radiation doses are received. Among the delayed effects thus far observed have been an increased potential for the development of cancer and cataracts. Since some forms of cancer are among the most probable delayed effects, the established dose limits were formulated with this risk in mind. These limits are set such that the calculated risk of cancer in radiation workers is an increase of a very small fraction of the normal cancer risk. (More on risk in a moment) • Genetic, or heritable effects appear in the future generations of the exposed person as a result of radiation damage to the reproductive cells. Genetic effects are abnormalities that may occur in the future generations of exposed individuals. They have been extensively studied in plants and animals, but risks for genetic effects in humans are seen to be considerably smaller than the risks for somatic effects. Therefore, the limits used to protect the exposed person from harm are equally effective to protect future generations from harm. PRENATAL RADIATION EXPOSURE • Since an embryo/fetus is especially sensitive to radiation, (embryo/fetus cells are rapidly dividing) special considerations are given to pregnant workers. Protection of the embryo/fetus is important because the embryo/fetus is considered to be at the most radiosensitive stage of human development, particularly in the first 20 weeks of pregnancy. • Limits are established to protect the embryo/fetus from any potential effects which may occur from a significant amount of radiation. This radiation exposure may be the result of exposure to external sources of radiation or internal sources of radioactive material. • Once a pregnancy becomes known limit embryo fetus dose equivalent to 50 mrem per month, excluding medical exposure. •Potential effects associated with prenatal radiation doses include: – Growth retardation – Small head/brain size – Mental retardation – Childhood cancer • At present occupation dose limits, the actual probability of any of these effects occurring in the embryo/fetus from occupational exposure of the mother is small. Evidence Of Radiation Carcinogenesis:
• 5.
  Radium dial painters Radiologistsand dentists Uranium miners Atomic bomb survivors Patients receiving medical procedures ANNUAL DOSE LIMITS: Occupationally exposed workers:  5rem/yr - whole body, gonads  15rem/yr – lens  50 rem/re – other organs, hands Non-occupationally exposed worker (and the general public)  0.1 rem/yr (100rem) REFERENCE: 1. http://www.srmuniv.ac.in/sites/default/files/downloads/BIOLOGICAL_EFFECTS_OF_R ADIATION.pdf 2. http://webfiles.ehs.ufl.edu/rssc_biological_effects_ionizing_rad.pdf