Lecture
Pathways of radionuclide entry into food and the human
body. The human body, and the plant and animal world, are constantly exposed to
the effects of ionizing radiation, consisting of natural (cosmic
radiation, radiation from radioactive gases from the upper layers
of the earth's crust) and artificial (X-ray equipment, television devices,
radioisotopes, nuclear-powered vessels, nuclear power plants, nuclear tests)
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radioactivity.
The radioactivity of plants and animals, and therefore of food products, is caused by all the isotopes that enter them from the sources mentioned. Isotopes are divided into two groups. The first group includes radionuclides that
are present in a mixture with stable elements participating in the metabolism
of substances in plants and animals (40K, 14C, 3H), the second group includes all the rest.
The most active nuclide is potassium-40, but its amount in products of plant origin, compared to its content in the earth's crust, is lower
by 3-10 times. The potassium content in animal organisms is even lower (10-15 times
lower than in rocks) [2, 5].
Artificial radioactivity occurs in stable chemical elements
when they are irradiated by streams of neutrons, protons, or particles.
All sources of radioactive radiation make up what is called the
natural radiation background, by which is meant the dose of ionizing radiation consisting of cosmic radiation and the radiation of natural radionuclides located in the upper layers of the
Earth, the surface atmosphere, food, water, and the human body.
Radioactive substances enter the air, soil, rivers, lakes,
seas, and oceans, and from there are absorbed by plants, fish, animals, and mollusks. Through leaves and roots, radioactive substances enter plants, then the bodies of animals, and with products of plant and animal
origin, along with water – the human body.
The effect of ionizing radiation on the human body. When studying
the effects of radiation on the human body, the following features have been established:
even a small amount of absorbed radiation energy
entails profound biological changes in the body;
the presence of a latent (incubation) period of action of ionizing
radiation;
radiation has a genetic effect;
the organs of a living organism have different sensitivity to radiation;
individual organisms react differently to irradiation;
the effect of irradiation depends on frequency. A single exposure
at a high dose entails more profound changes.
Radioactive substances enter the human body through inhalation
of contaminated air, with contaminated food or water, through the skin, or open wounds. Penetration of radioactive contaminants through the skin and wounds can be prevented by observing certain protective measures. The main source
of human exposure is radioactive substances that enter with food.
The degree of danger of contamination with radionuclides depends on the frequency
of consumption of products contaminated with radioactive substances, as well as
the rate of their elimination from the body. If the radionuclides that entered the
body are of the same type as elements consumed by humans with food (sodium,
potassium, chlorine, calcium, iron, manganese, iodine, etc.), they are quickly excreted from the body along with them [2, 5].
Certain radioactive substances concentrate in various internal
organs. Elements accumulated in the soft tissues of the body are easily
excreted. Sources of α-radiation (radium, uranium, plutonium), β-radiation (strontium, yttrium), and γ-radiation (zirconium) are deposited in bones in the form of chemically bound compounds with bone tissue,
and therefore are difficult to eliminate from the body.
Certain substances in food products (pectin substances, dyes) form insoluble compounds with strontium, cobalt, lead, calcium, and other heavy metals, which are not digested and are eliminated from the body. Consequently, these substances perform a radioprotective function. Therefore pectin, and
also pectin-containing products (black currants, gooseberries, strawberries, etc.),
are used in special diets for the removal of radioactive
elements from the body
The primary process of the action of radioactive substances in the human body
is ionization. The energy of ionizing radiation excited in this process is transferred to various substances of the human body. When acting on simple substances
(gases, metals, etc.) no changes in their physicochemical nature are observed. When acting on complex substances, whose molecules consist of
many different atoms, they break down (dissociation). This is the so-called direct action on simple or complex substances of the human body.
A more significant role is played by the mechanism of indirect action of ionizing radiation, by which should be understood radiation-chemical changes in a certain
soluble substance, caused by the products of radiolysis (decomposition) of water. The human body contains 60–70% water. As a result of ionization of water
molecules under the influence of radioactive substances, free radicals of
hydrogen hydroperoxide (HO2) and peroxide (H2O2) are formed, which, as strong oxidants, possess high chemical activity and enter into reactions with protein, enzymes, and other structural elements of biological tissue
entails changes in biological
processes in the body: metabolic processes are disrupted
enzyme system activity is inhibited, tissue growth is delayed
new chemical compounds (toxins) and strong poisons arise. All this
leads to disruption of the vital functions of individual systems and the organism as a
whole [2, 5].
Pathological processes in the body, including cell death and tumor
growth, are associated with chromosomal damage to somatic cells,
and the level of autogenous chromosome damage increases with human age.
At present, based on numerous radiobiological experiments at the cellular and molecular levels, the concept of a threshold-free dependence of the "dose-biological effect" relationship has been unambiguously accepted, according to which even a single
track left by a charged particle of matter creates a striking
effect capable of causing disruptions in the hereditary apparatus of the cell, including
mutations, which leads to its endogenous transformation. The thesis on the absence of a threshold for the damaging action of radioactive exposure and the absence of
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safe doses is set out in the decisions of the International Commission on Radiological Protection (ICRP), the International Atomic Energy Agency
(IAEA), and the Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) under the UN.
The Commission on Radiological Protection (CRP) under the Ministry of Health
adopted a special decision, according to which exposure at any
however small a dose is associated with a risk of carcinogenesis, disruption of
metabolism, suppression of the immune system, shortening of life, and other consequences [2, 5].
Consequently, it can be asserted that consumption of food products which
contain radionuclides within the permissible levels approved by the Chief
State Sanitary Physician of Ukraine is not safe for the human body. The content of radionuclides in food is regulated by State Hygienic Standards (DR-2006) "Permissible levels of content
of radionuclides 137Cs and 90Sr in food and water", approved by the Chief State Sanitary Physician of Ukraine on May 3,
2006, No. 256.
The State Hygienic Standard DR-2006 regulates the content of radionuclides 137Cs and 90Sr in water and food products sold on the territory of Ukraine or imported into the territory of Ukraine for sale, and is introduced with the aim of further reducing the internal exposure dose of the population of Ukraine by limiting the intake of radionuclides through compliance with clean production in contaminated territories.
DR-2006 has been established on the basis that the content of radionuclides 137Cs and
90Sr in food and water must ensure that the
limit of the annual effective dose of internal exposure of 1 mSv (table
2.2) is not exceeded. In this case, exposure due to the intake of other man-made
and natural radionuclides is not taken into account. Control of the content of 137Cs and 90Sr in
food products and water is carried out on the basis of applicable standards
and methodological guidelines agreed with the Chief State Sanitary Physician of Ukraine [2, 5].
Possibilities for reducing the concentration of radionuclides in food and recommendations on the diet of people. With the proper diet
of people living under conditions of radioactive contamination of
territory, the intake of radionuclides into the body can be reduced. In
this case, it is important to maintain the completeness of nutrition so that all elements necessary for the body – proteins, fats, carbohydrates, organic acids,
vitamins, minerals, and dietary fiber (fiber, hemicellulose, pectin, etc.) – are present in the diet in sufficient quantity.
Milk, cream, and fermented milk products are capable of accumulating
radionuclides. The main part of them combines with proteins and is contained in the protein-lipid membranes. Therefore the content of radioactive strontium-90 and cesium-137 is lower in dairy products with a high fat content and low-
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er protein content, and vice versa. In the production of fermented milk products from milk, buttermilk and whey are formed, in which the main
part of the radionuclides contained in the milk remains. Therefore, before consumption, they
must be specially treated with precipitants of radioactive substances. This
can remove up to 90% of strontium-90 [2, 5].
Table 2.2 – Permissible levels of radionuclide content
Product types
137Cs,
(Bq/kg, Bq/L)
90Sr,
(Bq/kg, Bq/L)
Bread and bread products 20 5
Potatoes 60 20
Vegetables (leafy, root crops, table greens) 40 20
Fruits 70 10
Meat and meat products 200 20
Fish and fish products 150 30
Milk and dairy products 100 20
Eggs, pcs 6 2
Water 2 2
Condensed and concentrated milk 300 60
Dry milk 500 100
Fresh wild berries and mushrooms 500 50
Dried wild berries and mushrooms 2500 250
Medicinal plants 600 200
Special infant food
products
40 5
Cheeses made from whole and skimmed milk have a high protein content,
which concentrates radionuclides, forming an especially strong complex with proteins
strontium-90. Cheeses produced by the most common rennet-coagulation method contain more radionuclides than those made by the acid-coagulation method.
Meat is capable of fixing radioactive strontium. In this case, in the bones
its concentration can be 1000
times higher than in muscle tissue.
Experiments have shown that during the boiling of meat, about 80% of cesium-137 passes into the broth, while for strontium-90 it is hundredths of a percent. Therefore, for using broths from meat contaminated with various radionuclides, it is necessary to
take a differentiated approach. This is especially important because
up to 30% of daily meat consumption is used
for preparing first courses. The concentration of cesium-137 in fatty tissue is 4-10 times lower than in
muscle tissue.
Milk with elevated radionuclide content is used for the production of butter, rennet cheeses, and dry condensed milk, provided that
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further long-term storage is ensured.
Eggs accumulate more radionuclides in the shell, from which, when
boiled, they can pass into the edible part, which must definitely be
taken into account when consuming it.
Potatoes with radionuclide content below the established levels
are used after thorough washing with water followed by peeling.
Green vegetables – lettuce, spinach, and early cabbage – in the case of
elevated radionuclide levels being detected, are not allowed into sale and are disposed of on
site.
Cucumbers and tomatoes with an insignificant degree of radionuclide contamination can only be used after separating the upper layers
of the fruit along with the skin.
Berries (black currants, red currants, gooseberries, blueberries), which grow in zones of radionuclide contamination, absorb radionuclides very strongly and therefore
cannot be used as food. They should also not be processed into compotes, preserves,
or jams, since the radionuclides in these processed products
do not change.
The content of radionuclides in food products is significantly reduced during
appropriate technological and culinary processing. At home
it is necessary to remove the top leaves from vegetables, wash vegetables, fruit, and berries well in
running water and peel them; mushrooms and wild berries should be soaked in cold
water for 2-3 hours, and under conditions of increased radionuclide contamination should be boiled, since part of the radionuclides, as well as nitrates and heavy metals, pass into the broth [2, 5].
Preliminary soaking helps reduce the activity of radionuclides.
Removal of the covering tissues of vegetables helps reduce the content
of radionuclides, because the specific effectiveness of covering tissues, for example,
of carrots is higher by 21.4%, of table beets – by 46.8%, compared to
the flesh.
The diet can be changed so that it promotes the elimination from the body
of strontium and cesium. Since strontium is eliminated by many organic
acids and pectin substances, more juices should be drunk, and
ecologically clean and fresh vegetables and their processed products should be consumed. Pectin substances are found in many fresh fruits and their processed products – marmalade, jelly, preserves, and dried fruits.
Salt exchange increases with the consumption of mineral water. To
reduce the concentration of impurities in tap water, filters can be used.
Cesium is eliminated from the body under the influence of its chemical analog,
potassium. Therefore, it is necessary to ensure that the diet contains a sufficient amount of this element in a biologically available form. Potassium is abundant
in such products as parsley, celery, spinach, sorrel, horseradish,
potatoes, curdled milk, milk mixtures, raisins, sultanas, dried apricots (uryuk), dried apricots (kuraga),
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kaisa, black currants, mulberry, etc.
It is very important to maintain a sufficient level of carotene in the diet, which is found in many fruits and vegetables – apricots, persimmons, sea buckthorn, black chokeberry, carrots, spinach, green onions, tomatoes, sweet peppers, pumpkin, etc. A deficiency of butter and sour cream is compensated
by increasing the consumption of oil.
Food industry enterprises produce special radioprotective products enriched with pectin, sodium alginate
(contained in laminaria seaweed), rutin, vitamin C (~
carotene, chicory, dietary fiber – cellulose, hemicellulose,
and lignin, etc.
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