Iodine prophylaxis in case of accident with release of radioactive iodine in the environment
IODINE PROPHYLAXIS – preventive protection measure aimed to avoid the health damage of individuals resulting from accumulation of radioactive iodine in the thyroid in case of nuclear or radiation accident.
The iodine prophylaxis is performed by taking tablets, frequently potassium iodine (KI), containing stable (not radioactive) iodine. These is the way in advance to saturate (blockade) the thyroid with stable iodine and to avoid the incorporation of radioactive iodine into the gland through inhalation or ingestion of materials (food, milk, water) contaminated with radioactive iodine in case of nuclear or radiation accident.
The requirements and order of implementation of iodine prophylaxis are defined with special legislature.
THE IODINE PROPHYLAXIS SHOULD NOT BE APPLIED WITHOUT PERMISSION AND WITHOUT EXPLICIT INSTRUCTIONS.
The iodine is a chemical element with atomic number 53 in the Periodic Table of Elements (“iodine” in translation form Greek means “violet”). This element has been discovered in 1811 and has only one stable (not radioactive) isotope with mass number 127 (iodine-127). The natural iodine is contained in the earth crust (10-4 %), in see water and seaweed. The iodine and its compounds are used in medicine and pharmacy. The alcohol solution of iodine (iodine tincture) has antiseptic characteristics. At present 22 isotopes of the iodine are known with mass numbers in the ranges 117 – 126 and 128 – 139. They are produced artificially during the nuclear fission process of nuclear fuel at the reactors or nuclear reactions. The radioactive isotopes of the iodine (iodine-131, iodine-125, iodine-129, etc.) have broad applications mainly in medicine (nuclear diagnostic and therapy) and science.
The most important radioactive isotope of the iodine from radiation protection point of view is iodine-131 (with half-life 8 days) to which a special attention is paid in case of nuclear or radiation accidents. Significant part of the activity of radioactive substances, which can be released in the atmosphere, in case of nuclear accident in a nuclear power plant, is created precisely by iodine-131. Other radioactive isotopes as iodine-125, iodine-133, iodine-134 and iodine-135 have shorter half-live and for the internal exposure of the individual their contribution is smaller in comparison with iodine-131.
Other special feature of the iodine is the fact that he relatively easily and quickly can penetrate in the milk (through the chain: grass/feedingstuffs – animal – milk-human).
The thyroid gland has a very small mass (about 20 g average for individuals) and when radioactive iodine (iodine-131) is accumulated this leads to receiving high exposure (absorbed doses) of critical human organ.
Within the first hours after occurrence of the nuclear or radiation accident the radioactive iodine-131 is entering into the body mainly through inhalation and rapidly is penetrating into the blood. To avoid the accumulation of iodine-131 in the thyroid gland potassium iodine tablets are used. The aim is to saturate in advance the thyroid with stable (not radioactive) iodine and in this way to block the subsequent intake of radioactive iodine. The radioactive iodine-131 can be accumulated in the body also through the food chain in the late phase of nuclear or radiation accidents. Besides the iodine prophylaxis, to reduce the exposure additional preventive measures should be applied such as suppression or restriction of consummation of feedingstuffs contaminated with iodine-131, strengthening the monitoring of milk, water and main feedingstuffs, as well as other organizational and administrative measure.
In order to be effective the iodine prophylaxis should be implemented opportunely taking into account the time, which it is necessary for the stable iodine (in the form of potassium iodine tablets) to saturate the thyroid. This time depends on the biological and physiological features of the single individual, as well as on the age and gender. The accumulation speed of the radioactive iodine-131 into the thyroid of children and pregnant women is higher than in other population groups. Critical groups are the newborns and children up to 12 years old, pregnant women and breast-feeding women. The risk of exposure of the thyroid to radioactive iodine-131 is negligible for adults over 45 years and hence iodine prophylaxis for them is not compulsory.
It is determined that the iodine prophylaxis is most efficient when it is implemented within the firs two hours after the nuclear or radiation accident whose consequences impose implementation of such protection measure for the population. If the iodine blockage is performed 5 hours after the accident the efficiency of these protection measure decreases 10 times.
According to the Regulation on Emergency Planning and Emergency Preparedness in Case of Nuclear and Radiation accident the iodine prophylaxis (stable iodine blockage of the thyroid) is the main protection measure for the personnel (of the facilities and the emergency personnel) and the population. In the country organization has been established for conducting iodine prophylaxis and potassium iodine tablets (KI) in sufficient quantities has been assured. The procedure and order for implementation of iodine prophylaxis is established in the National Emergency Plan (off-site plan).
The Regulation No.28 issued by the Minister of Health establishes the conditions and order for medical assurance and health norms for protection of the individual in case of radiation accident, as well as the intervention levels and dosages of the potassium iodine tablets for iodine prophylaxis. The following six age population groups are determined by the regulation: newborns and babies up to 2 months, children up to 3 years old; children from 3 years up to 12 years; young people and adults from 12 up to 45 years and pregnant women and breast feeding women. One standard potassium iodine tablet is 65 mg and contains 50 mg stable iodine (iodine-127). The dosage of the stable iodine differs for each one of the 6 determined groups and has been defined by the Regulation No.28. The maximum amount of stable iodine intake is 1 g during 10 days. These means that individuals older than 12 years should take only two pills per day (2 x 65 mg) and no longer than 10 days. For all other groups the daily dosage is from 2 to 8 times less (for newborns up to 2 mounts are allowed to take once only ¼ part from the standard pill of 65 mg potassium iodine).
The iodine tablets should be taken only after consultations with a medical doctor and in case of the following diseases:
- disturbance of the functions thyroid gland;
- bronchitis asthma;
- pelvis insufficiency;
- immunity insufficiency.
Method of intake of iodine tablets:
The tablets should be taken after eating and they should be crushed and taken with large amount of liquids to avoid and minimise the undesirable irritation of the gastro-intestinal system.
Potential side-effects during intake of iodine tablet:
- metallic taste;
- nausea and vomiting;
- gastric disorders;
- skin rashes;
The iodine tablets protect only the thyroid from accumulating radioactive iodine but do not protect against other radioactive substances, which also are released in case of nuclear or radiation accidents.
The responsibility for assuring, storage and distribution of the potassium iodine tablets for protection of the population in case of nuclear or radiation accident is assigned to the Ministry of Emergency Situations (MES) through the General Directorate “National Service Civil Protection” and its regional services, as well as to the local authorities.
All necessary quantities of potassium iodine tablets for the entire Bulgarian population are assured in compliance with the national legislation for emergency planning and response in case of nuclear or radiation accidents.