After reading this article you will learn about:- 1. Meaning of Radiation Hazards 2. Source of Radiation Hazards 3. Dose and Dose Rate 4. Mechanism Radiation Toxicity 5. Radiation Toxicity.
Meaning of Radiation Hazards:
Radiation is defined as energy traveling through space. Non- ionizing radiation is essential to life, but excessive exposures will cause tissue damage. All forms of ionizing radiation have sufficient energy to ionize atoms that may destabilize molecules within cells and lead to tissue damage.
Radiation sources are found in a wide range of occupational settings. If radiation is not properly controlled it can be potentially hazardous not only to the health of workers but also nearby man and animal population.
Radiation hazards occur mainly as result of four types of radiation due to positively charged alpha particle or positrons, negatively charged beta particle, gamma rays and X-rays.
An atom can decay by loosing a heavy positively charged alpha particle (He+) that consists of two protons and two neutrons or negative charged electron (beta particle) gamma radiation occurs when nucleus releases excess energy usually after loosing alpha, beta or positron transition. X-ray originate when inner shell orbital electron is removed and rearrangement of electrons resulting in emission of characteristic X-ray energy of the element.
Source of Radiation Hazards:
i. Non-Ionizing Radiation:
Electromagnetic radiation ranging from extremely low frequency (ELF) to ultraviolet (UV) comprise non-ionizing radiation. Non- ionizing radiation is described as a series of energy waves composed of oscillating electric and magnetic fields traveling at the speed of light.
Non-ionizing radiation includes the spectrum of ultraviolet (UV), visible light, infrared (IR), microwave (MW), radio frequency (RF), and extremely low frequency (ELF). Lasers commonly operate in the UV, visible, and IR frequencies.
Various instruments have sources emitting non-ionizing radiation such as microwave ovens, high pressure short-arc lamps (e.g. spectrophotometers and fluorometers), lasers, nuclear magnetic resonance (NMR) spectrometers, visual display terminals (VDTs), and U.V. lamps.
Non-ionizing radiation in occupational settings can pose a considerable health risk to potentially exposed man and animal population. The eye is the principal organ affected, followed by inflammation of other organs, fetal abnormalities, headache and fatigue.
ii. Ionizing or Nuclear Radiation:
Ionizing or Nuclear radiation differs from heat and other types of radiation in that each particle or photon has a sufficiently high energy to cause ionization. Radioactive particles are alpha, beta (electrons) and neutrons.
Alpha particles are helium nuclei consisting of two protons and two neutrons with a charge of +2 that are released from nucleus of an atom. After losing energy, an alpha particle acquires two electrons from the media and remains in the form of helium in the environment.
Thus all helium in the environment are the result of decay of alpha particles. Beta radiation consists of a high-speed electron with one unit of negative charge. Neutron is an uncharged particle that cannot cause ionization directly. It can transfer its energy to charged particles.
The electromagnetic radiation with high frequencies consisting of x-rays and gamma rays are ionizing radiation. Ionizing radiation is more energetic and likely to ionize material and directly affect cell chemistry, destroying cells or causing genetic damage which may lead to cancer.
The impact depends on the area affected, whether the energy is absorbed by the skin, or if radioactive materials are ingested or inhaled where they can react with vital organs.
iii. Electromagnetic Radiation:
Electromagnetic radiation includes both nuclear and non nuclear radiation, depending on the energy level. Electromagnetic nuclear radiation may comprise of gamma rays and X-rays. X-rays and gamma rays, with short wavelength and high energy, transfer their energy, as neutrons, to charged particles.
Non-Nuclear Radiation comprises electromagnetic radiation, including ultra violet (U.V.), Lasers, Radio Frequency (R.F.), for example microwaves and Infra Red (I.R.). The essential difference between the two types of radiation lies in their origin, whereas gamma rays result from changes in the nucleus and x-rays are produced by different x-ray machines.
The sun shine is the most familiar form of electromagnetic (EM) radiation, which provides light and heat. Sunshine consists primarily of radiation in infrared (IR), visible, and ultraviolet (UV) frequencies. Lasers also emit EM radiation.
Electromagnetic radiation may be considered as a type of wave with a wide spectrum of frequencies and wavelengths. There is an inverse relation between wave length and energy as the wavelength of radiation decreases, the energy and it’s potential to ionize biological matter increases.
iv. Extremely Low Frequency Radiation (ELF):
Extremely Low Frequency (ELF) radiation at 60 HZ is produced by power lines, electrical wiring, and electrical equipment. Common sources of intense exposure include ELF induction furnaces and high-voltage power lines.
v. Radio Frequency and Microwave Radiation:
Microwave radiation (MW) is absorbed near the skin, while Radiofrequency (RF) radiation may be absorbed throughout the body. At high intensities both will damage tissue through heating. Sources of RF and MW radiation include radio emitters and cell phones.
vi. Infrared Radiation (IR):
The skin and eyes absorb infrared radiation (IR) as heat manifested by heat sensation and pain. Sources of IR radiation include furnaces, heat lamps, and IR lasers.
vii. Visible Light Radiation:
The different visible frequencies of the electromagnetic (EM) spectrum are “seen” by our eyes as different colors. Good lighting is conducive to increased production, and can help prevent incidents related to poor lighting conditions. Excessive visible radiation can damage the eyes and skin.
viii. Ultraviolet Radiation (UV):
Ultraviolet radiation (UV) has a high photon energy range and is particularly hazardous because there are usually no immediate symptoms of excessive exposure. Sources of UV radiation include the sun, black lights, welding arcs, and UV lasers.
ix. Laser Hazards:
Lasers typically emit optical (UV, visible, IR) radiations and are primarily may cause an eye and skin hazards. Common lasers include CO2 IR laser; helium – neon, ruby visible lasers, and the Nitrogen UV laser.
x. Radiofrequency (RF) and Microwave (MW) Radiation:
Radio frequency (RF) and microwave (MW) radiation are electromagnetic radiation in the frequency ranges of 3 kilohertz (kHz) – 300 Megahertz (MHz), and 300 MHz – 300 gigahertz (GHz), respectively.
Research continues on possible biological effects of exposure to RF/MW radiation from radios, cellular phones, the processing and cooking of foods, heat sealers, vinyl welders, high frequency welders, induction heaters, flow solder machines, communications transmitters, radar transmitters, ion implant equipment, microwave drying equipment, sputtering equipment and glue curing.
Electric and magnetic fields are complex physical agents which may affect biological systems by biophysical mechanisms and may include carcinogenic, reproductive and neurological effects. Health effects by exposure source are noted in radar traffic devices, wireless communications with cellular phones, radio transmission, and magnetic resonance imaging (MRI).
xi. Ultrasonic Radiation:
Ultrasonic radiation consists of high speed sound vibrations that can only promulgate through a suitable medium, such as air or water. Ultrasonic radiation is used for diagnostic, cleaning, and chemical purposes.
Concentrated beams of ultrasound waves can be focused on a target, and reflected vibrations detected can be displayed as a moving image (e.g. echo reflection ultrasonography). The type of radiation, the environment and the health status of the biological organism are important for biological damage likely to be encountered from exposure to ultrasonic radiation.
Dose and Dose Rate:
The absorbed dose of radiation is expressed in the unit of gay (Gy) which is the mean energy imparted by ionizing radiation to a unit of mass. One gay radiation is equal to 1 J kg. The older unit of dose is rad, which is equal to 100 erg g_1 and is numerically 100 times the dose in gay i.e., 100 rad = 1 Gy.
For uncharged particles such as gamma rays and neutrons, sometimes kerma (kinetic energy related in matter) is used in the same units as those of dose. Kerma is the sum of the initial kinetic energies of the all the charged ionizing particles liberated in unit mass. The units of kerma are same as those of dose. Dose rate is the dose expressed per unit of time.
Mechanism Radiation Toxicity:
Ionizing radiation comprising alpha and beta particles and gamma rays loses energy when passing through organic matter by releasing ion pairs of an electron and a positively charged atoms. Ionization can break the bonds in DNA and subsequently damage DNA.
These ion pairs rapidly interact with organic molecules in the tissue and produce free highly reactive oxidative species (ROS) radicals by forming super oxide O2” anion which subsequently converted to a strong oxidizing agent hydrogen peroxide.
Free radicals or H2O2 cause cellular damage by interacting and disrupting structure and function of proteins, amino acids, carbohydrates, nucleic acids, lipids, thiols etc. Damage to DNA results in mutation, chromosomal aberrations and loss of genes subsequently leading to cell death. The extent and rate of chromosomal aberrations is directly related to radiation dose.
There is a variation in susceptibility among different species of organism and also their organs to radiation toxicity as donkeys, rabbits, and poultry are less susceptible than man, dogs, pigs and goats and the organs with fast proliferating cells like skin, gastrointestinal tract and haematopoietic system are most affected with the exception of human lymphocytes. Young animals and foetus are more radiosensitive than adults. Depending upon dose and exposure of duration radiation may cause acute, sub-acute and chronic toxicity in man and animals.
Acute radiation toxicity:
Exposure to high doses of irradiation results in acute toxicity and is characterized by severe irritation of GIT resulting in intense and refractory diarrhea, dehydration, redness of skin, thirst, weakness, recumbency, rapid respiration, panting, profuse and blood stained nasal discharge.
If animal survive, there may be severe depression of bone marrow manifested by anaemia, lymphopenia, agranulocytosis, thrombocytopenia, impaired blood clotting and antibody production, and necrosis of mucosa of GIT, loss of hair and ulceration of skin followed by secondary infections, degenerative changes in lens of eye (cataract), high rate of mutations, tumours mostly of haemopoietic system, particularly leukemia may be observed.
Death may occur due to dehydration and salt depletion few days or weeks post exposure. Most of the deaths in acute and sub-acute cases occur in 1-4 weeks of irradiation.
Sub-acute Radiation Toxicity:
Sub-acute toxicity occurs as result of low level radiation continuously for few weeks and is characterized by anorexia, vomition, depression and weakness followed by fever, knuckling at the fetlock, swelling of legs, diarrhea, dysentery, polydipsia, recumbency and hyperirritability and severe anaemia and septicemia in terminal stages leading to death 3-4 weeks post exposure.
Chronic Radiation Toxicity:
Prolong exposure of animals as result of ingestion of contaminated pasture may result in chronic toxicity. Consumption of milk, vegetables food grains etc. contaminated with radioactive material may be the source of chronic toxicity and is manifested by retarded growth alopecia, sterility, mutational changes, cancer of blood (leukaemia), thyroid, breast, lungs, colon, stomach, liver, urinary bladder and other tissues and teratogenesis.
Oedema of the dermis, swelling and ulceration of mucosa of gastrointestinal tract, severe congestion and fibrosis in lungs, hypertrophy of adrenals, atrophy and degenerative changes in bone marrow, lymphoid organ, testicles and hepatomegaly, ascites and jaundice are the major pathological lesion.
Diagnosis is made on the basis of history, clinical signs and pathological lesions.
There is no specific treatment for radiation toxicity. Symptomatic and supportive therapy may be given.