Ionizing radiation is a form of energy released by atoms in the form of electromagnetic waves such as gamma, x-rays or particles such as neutrons, beta or alpha. The disintegration of atoms is called radioactivity and the extra amount of energy released is a form of ionizing radiation. The elements that disintegrate and release ionizing radiation are called radionuclides. The measurement of the amount of a radionuclide present is expressed in a unit named Becquerel (Bq) and one becquerel is equivalent to one disintegration per second. The time required for the activity of a radionuclide to decrease by half of its initial value is called the half-life. The time it takes for one half of its atoms to disintegrate is called the half-life of a radioactive element.
The sources of radiation
The exposure of radiation can come from natural radiation sources and human made sources. The exposure of radiation from human made sources is coming mainly from nuclear power generation and from medical devices used to diagnosed medical conditions such as computed tomography (CT) scan and x-ray machines. The exposure of radiation from natural sources includes soil, water and air. An example of a natural occurring gas and a main source of radiation that emerge from rock and soil is called Radon. Radon is a radioactive gas that is colourless, tasteless and has no smell. Cosmic rays are also a form of natural radiation and people are exposed when they are at a higher altitude. It is estimated that 80% of the annual dose of background radiation is coming from terrestrial and cosmic radiation sources. It is also noted that radiation varies geographically, and the exposure can be higher than average in certain areas.
The exposure to ionizing radiation
The exposure to ionizing radiation can occur in different situations. This can occur at home, public spaces (public exposure), workplace (occupational exposure), and in hospital via medical devices (medical exposure). The exposure to ionizing radiation can occur through both the internal and external pathways.
The internal exposure to ionizing radiation occurs when the radioactive materials are ingested through contaminated water or food, inhaled through dust, aerosols containing radioactive particles, and through absorptions through skin such as contaminated wounds and injections. This type of exposure ceases when the radionuclides are eliminated from the human body either via treatment or spontaneously via excretion.
The external exposure to ionizing radiation occurs when the individual is exposed to radiation outside the body. This type of exposure can occur from several sources including environmental sources such as cosmic radiation, terrestrial radiation (soil, rocks, water), medical sources (x-rays, CT scans), radiation therapy (used in the treatment of cancer), industrial sources such as nuclear power plants, and consumer products such as smoke detectors as these contain minimal amounts of radioactive materials.
Protective measures to ionizing radiation
The risk of radiation exposure can be reduced through various protective measurements. These can be divided into external pathway and internal pathways.
External pathway protections occur via shielding such as materials like lead or concrete to stop radiation, timing, by limiting the amount of time spent near the source of radiation and distance by increasing the distance from the source of radiation.
Internal pathway protections occur via food and water safety by monitoring and controlling the levels of radioactive contaminants, air quality control by using ventilation to reduce radon levels and respirators when the environment is contaminated, and by using personal protective equipment such as gloves, mask, and protective clothing to absorption from skin and inhalation.
Health effects of ionizing radiation
The damage caused to tissues and organs by radiation depends on the dose of radiation received or absorbed dose which is expressed in unit called gray (Gy). Radiation damage also depends on the type of radiation and the sensitivity of the different tissues and organs.
Ionizing radiation is found to impose significant risk factor to human health. These include:
Ocular effects: The lens is not the most radiosensitive tissue in the human body, but due to its inefficient repair capabilities, allow radiation to build up with minimal repair hence can result in the formation of cataracts that can range from blindness to impaired vision. These negative effects might occur after the initial exposure but can occur later in life.
Reproduction: The reproductive tract of both males and female are at higher risk of ionizing radiations as they replicate at an accelerated rate. In males, spermatogonia are cells responsible for producing spermatocytes and later spermatids and mature sperm. The spermatogonia is very sensitive to the effect of ionizing radiation. On the other hand, spermatids and sperm are very radio resistance to the negative effects of radiation. Initially the reduction of the sperm count is not evident until significant exposure. In fact, azoospermia that is no sperm in the ejaculate is found to occur 10 weeks after exposure to > 1Gy of radiation. In addition, it is found that exposure to 6 Gy of radiation can result in permanent sterility. In females, the sensitivity of the mature oocyte is less than the male spermatogonia, but it is considered the most radiosensitive reproductive cell. It is found that exposure to 1.5Gy can result in temporary sterility.
Gastrointestinal Tract: High doses of ionizing radiation with prolonged exposure can negatively impact the gastrointestinal tract. This can result in cellular damage and vascular damage. At a cellular damage, the ionizing radiation can cause damage to the DNA of cells that line the gastrointestinal tract resulting in cell death, and impaired cell division. It can also cause vascular damage by causing reduction in the blood flow throughout the arteries causing ischaemia and increase the risk of tissue damage.
Cardiovascular system
The cardiovascular system is negatively affected following exposure to high doses of radiation. In fact, high doses that is >5Gy, is associated with significant risk of acute and chronic cardiovascular conditions. High dose of radiation can cause acute effects on the cardiovascular system, these are: pericarditis which is inflammation to the pericardium, (the sac surrounding the heart) causing chest pain and fluid accumulation around the heart and myocarditis which is an inflammation to the myocardium (heart muscle), causing chest pain, fatigue and also irregular heart rhythm known as arrhythmias. High dose of radiation can also cause chronic effects on the cardiovascular system including coronary artery disease which increase the risk of atherosclerosis (thickening or hardening of the arteries causing narrowing of the lumen of the arteries) hence increase the risk of heart attacks , cardiomyopathy which can impair the ability of the heart to pump blood effectively, heart valve disease because radiation can cause calcifications and fibrosis of the heart valves hence leading to valvular stenosis or regurgitation, and hypertension.
Respiratory system: The lungs are radiosensitive organ hence significant exposure is a risk factor to cause respiratory diseases. In fact, ionizing radiation can cause direct damage to the tissues of the lung at cellular level, causing inflammation, necrosis and scarring of lung tissues. This can lead to conditions such as pneumonitis (inflammation of the lung) and pulmonary fibrosis (Scarring of lung tissue), hence reducing lung function.
High doses of ionizing radiation (over 0.5Gy) through the body can cause radiation poisoning or radiation sickness a condition known as acute radiation syndrome. This can cause coughing, shortness of breath, low levels of oxygen in view of damaged epithelium.
Diabetes: Diabetes is associated with various diseases including cardiovascular diseases hence it becomes a major public health concern. Research have shown that atomic bomb survivors from Hiroshima and Nagasaki, showed that exposure to the radiation might be associated with an increased risk of diabetes specifically to those exposed at a younger age. In addition, patients receiving radiation therapy for the management of cancer, such as abdominal or total body irradiation are found to have increased risk of diabetes due to direct or indirect involvement of the pancreas involved in the metabolism of glucose.
Skin: The radiation dose and the exposure are the vital parameters to determine the effect of ionizing radiation on the skin. Ionizing radiation is associated with increased risk of skin cancer such as basal cell carcinoma, squamous cell carcinoma, fibrosis of the skin, causing hardening and thickening of the skin due to formation of scar tissue and also radiation dermatitis, this occurs following long term exposure causing pigmentation, atrophy, and telangiectasia (small dilated blood vessels).
Ionizing radiation can have detrimental effects to the human body, however the basic principle of toxicology that is the dose determines poison can be applied to the toxicology of ionizing radiation. The best approach to be able to fully understand the risk of exposure of ionizing radiation is through molecular studies in which unique biomarkers and pathogenic pathways both at tissue and cellular levels are identified to aid in prevention of unnecessary ionizing radiation.
Renald Blundell is a biochemist and biotechnologist with a special interest in Natural and Alternative Medicine. He is a professor at the Faculty of Medicine and Surgery, University of Malta.
Jean Claude Grech is a medical doctor at Mater Dei Hospital.
Photo: AI-generated image created by Prof. Blundell