Chapter 18 - Biological effects of radiation

Abstract

Human beings are persistently exposed to background radiation from several naturally occurring and man-made sources. Radiation, howsoever small, has some biological effects; although the effects of ionizing radiation are more detrimental than those of non-ionizing radiation. Ionizing radiation has the capacity to penetrate the human body and damage the cell structure resulting in severe biological effects. The amount of biological damage caused by radiation is determined by the equivalent radiation dose absorbed by a particular tissue; the radiation effects being more pronounced in highly radio-sensitive cells such as those of stomach lining, gonads, epithelial cells, bone marrow, etc. Ionizing radiation can interact directly with the DNA or indirectly by creating reactive hydroxyl radicals that further damage the biological molecules. A dose–response curve is helpful in establishing a tolerable level of radiation exposure by correlating the dose imparted with its corresponding biological effect. Effects of high and low radiation doses can be represented by threshold and non-threshold dose–response curves, respectively. Radiation effects can be classified as somatic, genetic, deterministic, and stochastic depending upon the nature and timings of the effect. High radiation doses tend to kill cells; the effect is so pronounced that tissues and organs can be damaged immediately. This in turn may cause a rapid body response often called acute radiation syndrome (ARS). It is a very critical situation that generally occurs during nuclear mishaps and demands special care and medication. Bone marrow syndrome, gastrointestinal syndrome, and central nervous system syndrome are the subcategories of ARS. Biological dosimetry, wherein a track of radiation-induced changes in different biological parameters is monitored, is rapidly gaining attention to deal with nuclear emergencies. Research is being carried on various radiation biomarkers such as chromosome aberrations, lymphocytes count, biochemical changes, sperm analysis, neurophysiological variations, etc. This chapter summarizes the various types of radiation, their biological consequences, and the research undertaken in this field.