Basic Concepts in Hazardous Chemicals: Radiation

The first atomic bomb which was dropped on Hiroshima and Nagasaki caused extensive radiation poisoning. The probability of such an exposure occurring is increasing, what with greater medical and industrial use and transport of radioactive materials.

Disasters caused by industrial negligence involving radioactive elements have become one of the major concerns in the world today. Such nuclear spillages can occur anywhere in both developed or developing countries.

For example, in 1979, the incident involving the nuclear plant at Three Mile Island contaminated Susquehanna River in the United States. Then, in 1986, the world's worst nuclear accident at Chernobyl in the former Soviet Union took place. Recently, experts are already warning of a second catastrophic explosion which might occur any time at Chernobyl.

Radiation is defined as energy in transit in the form of high speed particles and electromagnetic waves. In other words, under certain circumstances, changes may be brought about within the atoms of almost any element. These subatomic changes involve the particles that make up the nucleus core of the atom and energies that are released during these reactions. Classification of radiation is based on how much energy it gives up to neighbouring material.

There are two types of radiation: particulate and electromagnetic. Particulate radiation include alpha rays and beta rays. Alpha rays consist of two protons and two neutrons. Alpha rays are the same as helium nuclei (helium atoms without electrons) and are emitted from the nuclei of radioactive atoms, as occurs in the radioactive decay of the heavy elements uranium, radium, and plutonium. Alpha particles have great ionising power but little ability to penetrate. They travel only a few centimeters and may be stopped by paper or the keratin layer of the skin.

Beta rays are electrons and are usually emitted from the nuclei of radioactive atoms of lighter elements. They travel a few metres and barely penetrate the skin.

Alpha and beta rays are considered non-penetrating radiation but are harmful if they contaminate open wounds or are ingested or inhaled. Alpha and beta contamination of body surfaces can be detected by Geiger-Muller counters.

Electromagnetic (EM) radiation is described in wave-lengths. These are the type of energy that we encounter and use every day. They're made up of visible light, radio and television waves, ultraviolet light, microwaves and the more energetic gamma and X-rays.

Gamma rays and X-rays are the two most common causes of radiation poisoning. They travel great distances and can penetrate body cells and cannot be detected by Geiger-Muller counters. Such radiation can be a carcinogen or a mutagen, but it has no smell or taste and it cannot be felt or heard. Its presence may not be noticed - until damage has been done.

According to a study in the United States, an adult human body is exposed to about 0.36Gy of radiation every year. Most of the radiation comes from natural sources around us. Sources of background radiation include cosmic rays (high energy particle ray and electromagnetic waves from space), cosmic inducible rays (formation of 14C and 1H in the atmosphere by cosmic rays) and natural radiation from earth such as uranium, thorium and radon. Natural radiation rarely causes serious health problems.

Background or natural radiation contributes 82% of the annual dose of radiation exposure to the human body. Continuous nuclear testing, nuclear warfare and radioactive leakage from nuclear power plants may increase the radiation level in the environment.

Radiation may cause injury by producing ionisation within cells. Body cells become ionised when radiation passes through and caus electrons to charge the atoms in the cell. These charged or ionised atoms will react with other atoms in the cells and cause damage. Enough damage then kill the cells. However, in low-dose radiation (natural radiation), the body is usually able to repair damaged cells.

Incidents of radiation exposure of the entire human body is based on the Japanese atomic bomb episodes, laboratory and reactor accidents, and radiotherapy. In general, following whole body exposure, acute radiation syndromes may be divided into cerebral, gastrointestinal, and haematopoietic syndromes.

The cerebral syndrome is distinguished by vomiting and drowsiness, followed by tremors, ataxia, and convulsions. Deaths usually occur within 24 to 72 hours. With acute whole-body doses in the range of 50Gy or more, one sees a constellation of prodromal, central nervous system, and gastrointestinal symptoms that include hypotension and shock leading to death.

The gastrointestinal syndrome occurs in the range of 6Gy to 20Gy of acute exposure, and is usually maximal three to five days after exposure. Vomiting and diarrhoea lead to severe fluid and electrolyte loss and clinical shock.

Radiation causes death of the crypt cells, resulting ultimately in the intestinal villi becoming denuded and ulceration and haemorrhage developing. If a patient can be supported with fluids, electrolytes, and blood replacement through this phase, regeneration of the gastrointestinal epithelia can be complete within two weeks.

The haematopoietic syndrome occurs with acute exposure in the range of 2Gy to 10Gy. Thrombocytopenia and neutropenia usually will not occur within 15 to 30 days. However, lymphopenia may occur within 48 hours as lymphocytes are highly sensitive to radiation. A valuable prognostic test is a complete blood count 48 hours after exposure. A lymphocyte count of 1200 or more per cubic milimetre is indicative of likely survival. A lymphocyte count of less than 300 per cubic milimetre suggests a poor prognosis.

Minimal exposures result in the occurrence of anorexia, nausea and mild to moderate vomiting which eventually subside.

Radiation burns may transpire as a result of immediate contact or exposure to a high-dose radiation source. The presenting complaint may be only an area of burning pain without any noticeable erythema. The physical findings may also be deceptively minor compared with the future extent of the injury, for radiation burns may develop much more slowly than thermal burns, often taking weeks to reach their full extent. Systemic symptoms may or may not occur and are dependent on the extent of penetration and duration and degree of exposure.

A major danger from radiation is radiation sickness. Radiation sickness is a condition that occurs when a person has been exposed to radiation over a long period of time. Leukaemia can be a result of radiation sickness. The federal government has established safety regulations to protect employees who work with radiation in factories, mines, or research. For example, people who work around radiation are required to wear special tags that monitor their exposure.

Another health problem results from the disposal of radioactive wastes. Radioactive wastes are wastes that give off radiation. Radioactive wastes from nuclear plants, for example, are very difficult to dispose off safely because the radiation will last for thousands of years. Scientists are continuing to look for safe ways to dispose of radioactive wastes.

The long-term effects of radiation include carcinogenesis (especially leukaemia and cancers of the thyroid, lung, and breast) and hereditary mutations. Since it may take 30 to 50 generations for deleterious genetic effects to express themselves, it is still impossible to make any determination of its full effects on the survivors of atomic bombs at Hiroshima and Nagasaki. It is thus mandatory to keep exposure to radiation to an absolute minimum under all circumstances.

The writer is a Science Officer at the National Poison Centre, Universiti Sains Malaysia.