Health Effects of the Japanese Nuclear Accident
By Justin H. Joe, Ph.D.
The news from Japan of the recent nuclear crisis induced by a record breaking earthquake of magnitude of 9.0 on the Richter scale and subsequent tsunami struck fear into the hearts of people in Japan as well as the citizens of surrounding nations such as China and Korea. Common perception associates radiation exposure, and more specifically radioactivity, with cancer and other untreatable and long-lasting illnesses. Much of the perceived as well as real danger association with radiation can be attributed to its invisible and undetectable nature [1, 2]. This article examines the potential health effects of radionuclides of iodine-131 and cesium-137, which are believed to have been released in the accident in Japan and other similar accidents in the past [3, 4], as well as several ways to minimize long-term biological effects to people living in potentially affected areas.
Radioactivity of nuclides can be defined as the process of spontaneous transformation of the nucleus, generally with the emission of alpha or beta particles often accompanied by gamma rays . The process is referred to as decay or the disintegration of an atom. Different types of radiations are capable of displacing electrons from atoms in bio-molecules, thereby producing ions. High doses of ionizing radiation may produce severe skin or tissue damage. Because approximately 70% of the human body is composed of water, water molecules (H2O) are naturally the most common building block of organic tissue. Ionization of water usually results in the formation of a hydroxyl radical (OH) or hydrogen peroxide (H2O2). These molecules can attack a biomolecule or a cell, and destroy it .
From a public health standpoint, however, the long-term health hazard of radionuclides, e.g. iodine-131 and cesium-137, from nuclear disasters lies in their ability to enter the body. This is the reason radioisotopes emitting alpha and low energy beta radiation are fundamentally harmless outside the body, but they can produce radiation damage to the target organs when taken into the body. Their biological behavior in their target organs is governed by their chemical properties, and their radioactive properties allow them to irradiate tissues in which they are localized. For example, cesium-137 is considered potassium equivalent and is expected to behave like potassium. Thus potassium abundance affects physical absorption and distribution of cesium-137 when the elements are chemically analogous .
The two main means of exposure to the nuclides are inhalation and ingestion. Soluble particles, which are inhaled, are absorbed quickly from the lung and delivered in the body depending on their chemical properties . Insoluble particles are deposited on the bronchial mucosa and carried out of the lung by ciliary action. Finally they are swallowed. Sufficiently insoluble radionuclides are accumulated in the alveoli, small chambers of air in the lung. Such particles can be slowly repositioned to the pulmonary lymph nodes. Ingested or swallowed particles after inhalation can be absorbed from the gut and distributed to the target organ in the body.
There are three important isotopes that present significant health hazards when inhaled or ingested, which are iodine-131, and cesium-137 and strontium-90; these are cancer hazards for the thyroid gland and bone, respectively . Fortunately iodine-131, which is collected in the thyroid, decays relatively quickly with a half- life of 8 days. Moreover, its bioeffect can be diminished quickly during food-chain transport. On the other hand, cesium-137 and strontium-90 with half-lives of 30 years and 28 years, respectively, can remain far longer in the body unless metabolized or driven out before localizing in different body parts including bones [2, 8].
There are several ways to minimize harmful exposure to these radioactive particles. First, only fall-out radionuclides such as iodine-131 and cesium-137 from nuclear disasters can stick to a person’s skin. They can be washed off if not inhaled or ingested. If someone unintentionally walks through fall-out rain, he/she should breath through a wet handkerchief or gas mask, if available, to prevent dust inhalation . Second, potentially contaminated foods and water should be avoided to prevent any ingestion of these radionuclides. Third, certain drugs can mitigate the effects of internal contamination. These include potassium iodide to protect against thyroid accumulation of iodine-131 and Prussian blue to help remove the effects of radioactive poisoning from cesium-137 .
While estimated internal and external radiation doses from iodine-131 and cesium- 137 around Fukushima were above the public dose limit (1 mSv/y) established by the Nuclear Regulatory Commission , radiation exposure potency still exists in neighboring countries. Environmental monitoring in Fukushima as well as surrounding regions and countries and other long-term follow-up measures could further ensure radiation safety and reduce unnecessary exposure. In addition, populations residing in affected areas should be monitored for any occurrence of health issues.
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