What effect does radiation have on plants? The effect of radiation on plants. ionizing particle in
Introduction
Bibliography
INTRODUCTION
During the radioactive decay of nuclei, α-, β- and γ-rays are emitted, which have ionization ability. The irradiated medium is partially ionized by the absorbed beams. These rays interact with the atoms of the irradiated substance, which leads to the excitation of atoms and the pulling out of individual electrons from their electron shells. As a result, the atom becomes a positively charged ion. (primary ionization). The ejected electrons, in turn, themselves interact with oncoming atoms, causing secondary ionization. The electrons that have spent all the energy "stick" to neutral atoms, forming negatively charged ions. The number of pairs of ions created in a substance by ionizing rays per unit path length is called specific ionization, and the distance traveled by an ionizing particle from the place of its formation to the place where the energy of motion is lost is called run length.
The ionizing power of different beams is not the same. It is highest in alpha rays. Beta rays cause less ionization of matter. Gamma rays have the lowest ionization capacity. The penetrating power is the highest for gamma rays, and the lowest for alpha rays.
Not all substances absorb rays equally. Lead, concrete and water have a high absorbing ability, which are most often used to protect against ionizing radiation.
1 Factors that determine the response of plants to irradiation
The degree of damage to tissues and the plant organism as a whole depends on many factors that can be divided into three main groups: genetic, physiological and environmental conditions. Genetic factors include species and varietal characteristics of a plant organism, which are mainly determined by cytogenetic parameters (nucleus size, chromosomes and amount of DNA). Cytogenetic characteristics - the size of the nuclei, the number and structure of chromosomes - determine the radioresistance of plants, which is closely dependent on the volume of cell nuclei. Physiological factors include the phases and stages of plant development at the time of irradiation, the growth rate and metabolism of the plant organism. Environmental factors include weather and climatic conditions during the period of irradiation, the conditions of mineral nutrition of plants, etc.
The volume of the cell nucleus reflects the content of DNA in it, there is a relationship between the sensitivity of plants to radiation and the amount of DNA in the nuclei of their cells. Since the number of ionization inside the nucleus is proportional to its volume, the larger the volume of the nucleus, the more damage to the chromosomes will occur per unit dose. However, there is no inverse proportional relationship between the lethal dose and the volume of the nucleus. This is due to the fact that the number and structure of chromosomes in the cells of plants of different species is not the same. Therefore, a more accurate indicator of radiosensitivity is the volume of the nucleus per one chromosome, i.e., the ratio of the volume of the nucleus in the interphase to the number of chromosomes in somatic cells (briefly called the volume of chromosomes). On a logarithmic scale, this dependence is expressed by a straight line with a slope equal to 1, i.e., there is a linear relationship between the indicated characteristics (Fig.).
Radiosensitivity of various plants under chronic irradiation (according to A. Sparrow)
Dependence of the radiosensitivity of woody (a) and herbaceous (b) plants on the volume of interphase chromosomes (according to Sparrow, 1965): 1-acute exposure (exposure to R); 2 - chronic irradiation (exposure in R/day)
From this it follows that the product of two quantities - the dose (or dose rate) and the volume of the chromosome at a given degree of radiation damage - is a constant value, i.e., with a constant average number of ionization in each chromosome, the same probability of damage to the genetic material of the cell appears. This means that for radiation damage to plant cells, it is not so much the value of the specific absorbed dose (for example, per 1 g of tissue) that is essential, but the value of the radiation energy absorbed by the nuclear apparatus. The inverse proportionality of isoeffective doses to the size of the chromosomal apparatus means that the average amount of energy adsorbed by the chromosomes during the exposures necessary to cause a given effect is approximately constant within each plant group, i.e. for trees and grasses. Isoeffective dose- the dose that has the same (similar) effect.
The degree of ploidy of plant organisms also affects the resistance of plants to irradiation. Diploid species are more sensitive. Doses damaging polyploid species are higher. Polyploid species are resistant to radiation damage and other adverse factors, since they have an excess of DNA.
Of the physiological factors, the radiosensitivity of plants is affected by the growth rate, i.e., the rate of cell division. In acute irradiation, the dependence of radiosensitivity on the division rate obeys the Bergonier-Tribondo law: plants have greater radiosensitivity at the stage of the most intensive growth, slow-growing plants or their individual tissues are more resistant to radiation than plants or tissues with accelerated growth. Under chronic irradiation, an inverse relationship is manifested: the higher the growth rate, the less the plants are inhibited. This is due to the rate of cell division. Rapidly dividing cells accumulate a smaller dose during one act of the cell cycle and, therefore, are less damaged. Such cells are more able to tolerate radiation without significant functional impairment. Therefore, upon irradiation in sublethal doses, any factor that increases the duration of mitosis or meiosis should increase radiation damage, causing an increase in the frequency of radiation-induced chromosome rearrangements and a stronger inhibition of the growth rate.
Criteria for the effect of ionizing radiation on plants. Since radiosensitivity is a complex, complex phenomenon, determined by many factors, one should dwell on those assessment methods and criteria by which the degree of radiosensitivity of plants is judged. Usually, the following criteria are used as such criteria: suppression of mitotic activity during cell division, the percentage of damaged cells in the first mitosis, the number of chromosome aberrations per cell, the percentage of seed germination, depression in plant growth and development, radiomorphoses, the percentage of chlorophyll mutations, plant survival, and ultimately the result is a seed crop. For a practical assessment of the decrease in plant productivity from exposure to radiation, the last two criteria are usually used: the survival of plants and their yield.
Quantitative assessment of radiosensitivity of plants according to the criterion of survival is established by the indicator LD50 (or LD50, LD100). This is the dose at which 50% (or 70, 100%) of all exposed individuals die. The LD50 indicator can also be used in assessing crop losses as a result of radiation damage to plants. In this case, it shows at what dose of irradiation of plants their yield is reduced by 50%.
Radiosensitivity of plants in different periods of their development. In the process of growth and development, the radiosensitivity of plants changes significantly. This is due to the fact that in different periods of ontogenesis, plants differ not only in their morphological structure, but also in the different quality of cells and tissues, as well as in the physiological, biochemical processes characteristic of each period.
During acute irradiation of plants in different periods of ontogeny, they react differently depending on the stage of organogenesis at the time of the onset of irradiation (Fig.). Radiation causes damage to those organs in plants and a shift in those processes that are formed and proceed during the period of exposure. Depending on the magnitude of the radiation dose, these changes can be either stimulating or damaging.
Radiation damage to plants to one degree or another affects all organs and all functional systems of the body. The most sensitive "critical organs", damage to which determines the development and result of radiation damage to plants, are meristematic and embryonic tissues. The qualitative nature of the reaction of plants to their irradiation depends on the biological specificity of the morphophysiological state of plants during the period of accumulation of the main dose of radiation.
Fluctuations in plant radioresistance during ontogeny (Batygin, Potapova, 1969)
According to the defeat of the main shoot, all cultures show the greatest sensitivity to the action of radiation in the first period of vegetation (stages I and III of organogenesis). Irradiation of plants during these periods inhibits growth processes and disrupts the mutual coordination of physiological functions that determine shaping processes. At radiation doses exceeding their critical values for a particular crop (LD70), in all cases, the death of the main shoot of cereal plants is observed.
If plants are irradiated at the early stages of organogenesis (I and V), additional shoots are formed, which, under favorable season conditions, have time to reach maturity and produce a crop that compensates to some extent for the losses associated with the death of the main shoot. Irradiation of plants at the VI stage of organogenesis - during the formation of pollen mother cells (meiosis) - can lead to significant sterility and loss of grain yield. A critical dose of radiation (for example, 3 kR for wheat, barley and peas) during this period causes complete sterility of the inflorescences of the main shoots. Additional tillering or branching shoots that develop in these plants at a relatively late time do not have time to complete their development cycle and cannot compensate for yield losses from the main shoots.
When plants are irradiated at the same stage VI of organogenesis during the formation of mononuclear pollen grains, the resistance to the action of ionizing radiation in plants increases significantly. For example, when wheat is irradiated with a dose of 3 kR during the period of meiosis, the grain yield is practically equal to zero, while when plants are irradiated during the formation of mononuclear pollen, a yield decrease by 50% is observed. At subsequent stages of organogenesis, the resistance of plants to the action of radiation increases even more strongly. Irradiation of plants during flowering, embryogenesis and grain filling at the same doses does not cause a noticeable decrease in their productivity. Consequently, the most sensitive periods include seed germination and the transition of plants from a vegetative to a generative state, when the fruiting organs are laid. These periods are characterized by increased metabolic activity and high intensity of cell division. Plants are most resistant to radiation during the period of maturation and during the period of physiological seed dormancy (table). Cereal crops are more radiosensitive in the phases of budding, tillering and heading.
The survival of winter crops during their irradiation in the autumn-winter-spring period noticeably increases when winter crops are sown at the earliest of the established dates. This is obviously due to the fact that the irradiated plants, leaving before winter stronger, in a state of full tillering, turn out to be more resistant to the consequences of the action of radiation.
A similar regularity in the decrease in grain yield during irradiation of plants in different phases of development was also obtained for other crops. Cereal legumes have the highest radiosensitivity during the budding period. The sharpest decrease in the yield of vegetable crops (cabbage, beets, carrots) and potatoes is observed when exposed to ionizing radiation during the germination period.
All grain crops have maximum radiosensitivity in the booting phase. Depending on the biological characteristics of plants, there is some difference. Thus, oats show maximum radiosensitivity at the end of the tube entry phase and during the panicle formation.
Decrease in the grain yield of winter crops (wheat, rye, barley) depending on the irradiation of plants with γ-rays in different phases of plant development, % to non-irradiated control
The negative effect of external γ-irradiation has less effect on the productivity of grain crops when they are irradiated in the tillering phase. With partial damage to plants, increased tillering occurs and, in general, the decrease in yield is compensated by the formation of secondary tillering shoots. Irradiation of grain crops in the period of milky ripeness does not cause a noticeable increase in the sterility of ears.
2 The effect of external ionizing radiation on the body
2.1 Options for possible radiative forcing
Sources of ionizing radiation (radionuclides) can be outside the body and (or) inside it. If animals are exposed to radiation from the outside, then they talk about external exposure, and the effect of ionizing radiation on organs and tissues from incorporated radionuclides is called internal irradiation. In real conditions, various options for both external and internal irradiation are most often possible. Such options are called combined radiation injuries.
The dose of external exposure is formed mainly due to the impact of γ-radiation; α- and β-radiations do not make a significant contribution to the total external exposure of animals, since they are mainly absorbed by the air or the epidermis of the skin. Radiation damage to the skin by β-particles is possible mainly when livestock is kept in open areas at the time of the fallout of radioactive products of a nuclear explosion or other radioactive fallout.
The nature of external exposure of animals over time can be different. Various options are possible single exposure when animals are exposed to radiation for a short period of time. In radiobiology, it is customary to consider a single exposure to radiation exposure for no more than 4 days. In all cases where animals are exposed to external irradiation intermittently (they may vary in duration), there is fractionated (intermittent) irradiation. With continuous long-term exposure to ionizing radiation on the body of animals, they speak of prolonged irradiation.
Allocate common (total) exposure in which the entire body is exposed to radiation. This type of exposure occurs, for example, when animals live in areas contaminated with radioactive substances. In addition, under the conditions of special radiobiological studies, local irradiation, when one or another part of the body is exposed to radiation! With the same dose of radiation, the most severe effects are observed with total exposure. For example, when irradiating the whole body of animals at a dose of 1500 R, almost 100% of their death is noted, while irradiation of a limited area of the body (head, limbs, thyroid gland, etc.) does not cause any serious consequences. In the following, the consequences of only general external exposure of animals are considered.
2.2 Effect of ionizing radiation on immunity
Small doses of radiation do not seem to have a noticeable effect on the immune system. When animals are irradiated with sublethal and lethal doses, a sharp decrease in the body's resistance to infection occurs, which is due to a number of factors, among which the most important role is played by: a sharp increase in the permeability of biological barriers (skin, respiratory tract, gastrointestinal tract, etc.), inhibition of the bactericidal properties of the skin , blood serum and tissues, a decrease in the concentration of lysozyme in saliva and blood, a sharp decrease in the number of leukocytes in the bloodstream, inhibition of the phagocytic system, adverse changes in the biological properties of microbes permanently residing in the body - an increase in their biochemical activity, an increase in pathogenic properties, an increase in resistance and others
Irradiation of animals in sublethal and lethal doses leads to the fact that from large microbial reservoirs (intestines, respiratory tract, skin) a huge amount of bacteria enters the blood and tissues.! At the same time, a period of sterility is conditionally distinguished (its duration is one day), during which microbes are practically not detected in tissues; the period of contamination of regional lymph nodes (usually coincides with the latent period); the bacteremic period (its duration is 4-7 days), which is characterized by the appearance of microbes in the blood and tissues, and, finally, the period of decompensation of protective mechanisms, during which there is a sharp increase in the number of microbes in organs, tissues and blood (this period occurs in a few days before the death of the animal).
Under the influence of large doses of radiation, which cause partial or complete death of all irradiated animals, the body is unarmed both to endogenous (saprophytic) microflora and exogenous infections. It is believed that during the height of acute radiation sickness, both natural and artificial immunity are greatly weakened. However, there are data indicating a more favorable outcome of the course of acute radiation sickness in animals subjected to immunization prior to exposure to ionizing radiation. At the same time, it has been experimentally established that vaccination of irradiated animals aggravates the course of acute radiation sickness, and for this reason it is contraindicated until the disease resolves. On the contrary, a few weeks after irradiation in sublethal doses, the production of antibodies is gradually restored, and therefore, already 1-2 months after radiation exposure, vaccination is quite acceptable.
2.3 Terms of death of animals after exposure to radiation in lethal doses
With a single irradiation of farm animals in doses that cause an extremely severe degree of acute radiation sickness (more than 1000 R), they usually die within the first week after radiation exposure. In all other cases, lethal outcomes of acute radiation sickness are most often observed within 30 days after exposure.1! Moreover, after a single irradiation, most of the animals die between the 15th and 28th days (Fig.); with fractionated irradiation with lethal doses, the death of animals occurs within two months after radiation exposure (Fig.).
As a rule, young animals die earlier after irradiation in lethal doses: the mortality of animals is usually noted on the 13-18th day. For all age groups of animals irradiated in lethal doses, earlier death is characteristic at the highest doses of radiation exposure (Fig.). However, this phenomenon can be regarded more as a trend than a regularity, since there is a lot of experimental data on the early death of animals when they are irradiated with relatively low doses of radiation.
Mortality of sheep after external γ -exposure to lethal doses (Peich et al., 1968)
Mortality of goats exposed to fractionated x-rays (Tylor et al., 1971)
It should be borne in mind that with fractionated irradiation, the timing of the death of animals depends primarily on the dose rate. So, with daily irradiation of donkeys at a dose of 400 R, all animals died between the 5th and 10th days. In experiments where the dose of daily exposure was 50 and 25 R, the average life expectancy after the onset of radiation exposure was 30 and 63 days, respectively. In addition, life expectancy is strongly influenced by species characteristics of animals. With fractionated daily irradiation of pigs at a dose of 50 R, their average life expectancy turned out to be 205 days, which is 6.4 times higher than the average life expectancy of donkeys under the same conditions of radiation exposure.
Mortality of cows at various times after γ-irradiation (Brown et al., 1961)
2.4 Economically useful qualities of animals exposed to ionizing radiation
In principle, all farm animals exposed to ionizing radiation can be divided into two categories. The first category includes animals that have received lethal doses of radiation. Their life span from the moment of irradiation is relatively short, but in some situations the productivity of mortally affected animals may be of some interest.
The milk productivity of cows in the first 10-12 days after exposure to radiation changes slightly, and then drops sharply, and already 2 days before the death of animals, lactation completely stops. The meat productivity of animals, which is usually characterized by the dynamics of live weight, also changes insignificantly: the decrease in body weight in mortally affected animals (if it occurs), as a rule, does not exceed 5-10%. Egg-laying in laying hens exposed to lethal doses of radiation stops within the next 5-7 days. There is no need to talk about the wool productivity of lethally affected sheep, since they have intensive hair removal 7-10 days after exposure to radiation.
In animals surviving after exposure to lethal or sublethal doses (second category), productivity decreases for a short time. For example, when cows were irradiated 60 days before calving at a dose of 400 R, their milk production during the first 10-12 weeks was lower than the control by 5-10%. After repeated irradiation at a dose of 350 R 18 weeks after the start of lactation, milk yield decreased by 16% during the first week after irradiation, by 8% by week 5, and by 6 week 
the productivity of irradiated cows returned to normal. Tentatively, it can be considered that irradiation of cows in doses that can cause partial death of a dairy herd leads to a decrease in milk yield per lactation by an average of 5-8%.
Surviving animals exposed to radiation at semi-lethal doses (or close to them) also have other adverse effects. So, after double irradiation of pigs (480 rad + 460 rad after 4 months), a decrease in weight gain was noted: 2 years after radiation exposure, the irradiated animals had a body weight 45 kg lower than control pigs. The life expectancy of pigs is reduced by an average of 3% for every 100 rad of external exposure of animals (Fig.). When irradiating White Leghorn chickens at a dose of 800 R (the mortality of chickens was on average 20%), a noticeable decrease in egg laying is observed (Fig.).
Radiation doses that cause acute radiation sickness of mild or moderate severity usually do not significantly affect the productivity of farm animals. For example, after external γ-irradiation at a dose of 240 R for the next 40 weeks, the bulls had an increase in body weight of 131 kg (in the control group 118 kg). Pigs exposed to chronic irradiation at doses of 360–610 R (dose rate 1.4 R/h) had a sufficiently high average daily gain (500–540 g) throughout the entire exposure period and the subsequent 90 days of the experiment and did not differ from control groups (approximately 470 g). A similar picture was observed with fractionated irradiation of pigs at a dose of 50 R/day. No decrease in egg-laying was found in chickens after irradiation at a dose of 400 R, and at a dose of 600 R, egg-laying decreased by about 20% only in the first decade after exposure.
Thus, when farm animals are irradiated in the sublethal dose range, no significant changes in their productive qualities are observed (unless, of course, the animals are kept in normal conditions and provided with appropriate diets). When animals are irradiated with absolutely lethal doses, productivity decreases, but the quality of livestock products remains quite high. With long-term feeding to animals of products obtained from sheep and cows fatally affected by radiation, no pathological changes are observed both in those consuming these products and in their offspring. However, when using products from radiation-affected animals for nutrition, it is recommended to carry out bacteriological studies and appropriate culinary processing with particular care.
2.5 Reproductive capacity of animals
The gonads of animals are highly sensitive to the action of ionizing radiation. When males are irradiated with sublethal doses, radiation damage occurs to the seminiferous epithelium in the seminiferous tubules, as well as spermatogonia and spermatocytes; mature and formed spermatozoa are considered radioresistant. High doses of radiation cause almost complete destruction of the seminiferous epithelium and subsequent attenuation of sperm production, while irradiation of males with medium and low doses initially leads to a decrease in spermatogenesis, and then its gradual recovery is noted (Fig.). A decrease in the volume of the ejaculate, a decrease in the concentration and mobility of sperm in the ejaculate, the appearance of a large number of ugly spermatozoa, a decrease in the biological usefulness of the sperm and its fertilizing ability are very characteristic. In addition, the weight of the testicles decreases: with γ-irradiation of boars at a dose of 400 R, the mass of testicles decreased by 30%, and with irradiation of males at a dose of 500 R, it decreased by 3 times compared with the mass of testes in control males.
Influence of external γ - exposure of chickens at a dose of 800 R to the egg production of surviving chickens (Maloniy, Mrats, 1969)
Sperm production of boars exposed to external γ-irradiation in sublethal doses (Paquet et al., 1962).
Irradiation at a dose of 400 R in some boars causes long-term infertility (boar No. 5)
If the radiation doses are not too high, then over time there is a partial or complete restoration of the reproductive function in males. In experiments on rams, for example, it was found that with irradiation at a dose of 100 R, sperm quality is restored after 4 months, at a dose of 430 R - only after 12 months. Note that a similar recovery of sperm quality in irradiated boars and bulls was observed already after 56 months, i.e., approximately twice as fast as in rams.
Ionizing radiation also affects the reproductive function of females. In irradiated animals, all types of cells of a functioning ovary are damaged and partially die (especially primary and secondary follicles, mature eggs), astral cycles are disturbed. However, it should be borne in mind that soon after irradiation (even with average lethal doses), the reproductive function of females is restored and they can produce viable offspring. For example, there was no decrease in fertility in adult cows exposed to double (with a break of 2 years) radiation exposure at doses of 400 R.
The most severe consequences are observed when animals are exposed to ionizing radiation during their prenatal development. Most of the embryos die in the pre-implantation period, i.e., in the period when the developing fertilized egg has not yet been introduced into the thickness of the uterine mucosa (in sheep and pigs - in the first 13, in cows - in the first 15 days after fertilization), or undergoes resorption (resorption) immediately after implantation. When pregnant animals are irradiated during the period of the main organogenesis (in sheep - on the 17-19th, in pigs - on the 15-18th, in cows - on the 22-27th day), even at relatively low doses of radiation exposure (200- 300 R) in many cases, resorption of the embryo is possible, and surviving embryos experience growth retardation, the appearance of malformations, an increase in neonatal mortality, and a reduction in life expectancy. For example, cases of fused fingers of the fore and hind limbs in the offspring were observed during irradiation of pregnant females on the 12-14th day of pregnancy at a dose of 400 R. When animals are irradiated at later stages of pregnancy, the radiosensitivity of fetuses is somewhat reduced.
When studying the consequences of the action of ionizing radiation on the body during fetal development, an exceptionally high sensitivity of the reproductive system of the fetus to the action of radiation was found. Under chronic irradiation of sows during 108 days of pregnancy (γ-irradiation doses from 1 to 20 rad/day, duration of daily irradiation 22 hours), pregnancy in animals proceeded normally, the general condition of sows, the number of live piglets in the litter and their postpartum viability did not differ from the same indicators in the control groups of animals. At the same time, even when pregnant sows are irradiated at a dose of 1 rad/day, newborn piglets show a significant decrease in the total number of germ cells (in animals of both sexes). Thus, in boletes, the number of gonocytes (the primary precursors of germ cells) was only 3% of the control, and in females, the number of surviving oocytes was equal to 7% of the oocytes of control pigs. Irradiation in the uterine period of development was the cause of a decrease in sperm production (by 83%), an increase in the number of defective spermatozoa from 2.8% (control) to 11.4 ° / o, which led to infertility in 4 out of 10 boars. Despite a significant decrease in the number of primary and growing follicles in irradiated gilts, their reproductive ability in the first litter was the same as in control animals, but after re-mating 4 out of 23 sows were found to be infertile. Irradiation of pregnant sows at a dose of 0.25 rad/day practically does not affect the reproductive function of the offspring.
Bibliography
1. Annenkov B.N., Yudinneva E.V. Fundamentals of agricultural radiology. - M.: Agropromizdat, 1991. - 287 p.: ill.
2. Starkov V.D., Migunov V.I. Radiation ecology. Tyumen: FGU IPP "Tyumen", 2003, 304 p.
USEFUL RADIATION
If the Lord God did me the honor to ask
my opinion at the creation of the world, then I would
advised to create it better, and most importantly - simpler
KING ALFONSE OF CASTILE XIII CENTURY
Probably, each of us has repeatedly had the idea of how complex and ingeniously a living cell is organized. It seems to be thought out to the end and so perfect that it cannot be improved. In the process of evolution, options for optimal cell designs were reworked millions of times And millions of options were rejected. The most worked out, finished and perfect samples remained. But over the past decades, scientists have convincingly proved the possibility of improving plants and other organisms with the help of ionizing radiation and radioactive isotopes.
In Paris, in the Jardep do Plante district, there is a small house. It is the property of the National Museum of Natural History. There is a modest board on its wall, and on it is the inscription "In the laboratory of applied physics of the Museum, Henri Becquerel discovered radioactivity on March 1, 1896." Three-quarters of a century has passed since then. Did any of Becquerel's most perspicacious compatriots assume that seventy years later radioactive isotopes would be widely used in agriculture, biology, medicine? That tagged atoms will be reliable assistants to man in solving the most pressing problems? And that, finally, with the help of penetrating radiation of certain radioactive isotopes, it will be possible to increase the yield of grain?
Using ionizing radiation, it is really possible to change living organisms in the direction necessary for a person.
A few years ago in Moldova in the spring one could meet on the roads a van with an inscription on the body "Atoms for the World" This is not a simple truck, but a mobile irradiator for pre-sowing seed treatment Its "atom is a heart" - a large container with a gamma-active isotope of cesium -137 On the eve of sowing, a van leaves the field A truck with corn seeds drives up to it A belt conveyor is switched on Seeds are poured into a bunker with a radioactive isotope of cesium Completely iso- tared from direct contact with the isotope, the seeds are at the same time irradiated with gamma rays in the required dose Continuous jet grain runs through the bunker Then it gets on another conveyor and poured into bags on another car Pre-sowing irradiation of seeds is completed Seeds can be sown.
Why irradiate corn seeds? Pre-sowing training of seeds is a method of increasing the yield of agricultural crops. It can be used to speed up the maturation of plants and improve their useful qualities.
There are ten pots with corn seedlings of various heights on the laboratory table. Under the leftmost signature: “Control”, under each of the other numbers - 100, 300, 500, 800 .. And so on up to 40,000. different doses of radiation on the 13th day of vegetation.
When seeds are irradiated at a dose of 100 and 300 roentgens, the height of the seedlings is the same as in the control group. At an irradiation dose of 500 roentgens, the plants are one and a half times higher than the control. But then, as the dose increases, the size of the seedlings decreases. At a dose of 8000 roentgens, the plants seem to be dwarfs. At a dose of 40,000 they are barely visible.
A few pages later, a photograph is pasted in the same laboratory journal. These are the roots of the same plants. Almost the same pattern. At a certain dose of gamma rays, a sharp increase in growth, and then a gradual decrease. At high doses, root growth is sharply inhibited.
First, they put experiments in the laboratory. Then the experiments are repeated in the field. Experiments in the field are like a dress rehearsal in the theater, like the last exam, after which the results of experimental studies will be put into practice field for three years showed that seed irradiation at a dose of 500 roentgens increases the yield of green mass of corn by 10-28 percent Silage obtained from such plants contains more protein, fats, nitrogen-free substances, fiber, carbohydrates
And if you irradiate radish seeds.
There are two bunches of radishes of the same variety on the experimenter's table. The amount of radish in each bunch is the same. But the radish on the left is much thicker and fleshier. Compared to it, the radish on the right seems skinny. But the right bunch is an ordinary, so to speak, “normal” radish. The plump relative on the left is a radish grown from irradiated seeds. When the seeds of this variety are irradiated,! gamma rays at a dose of 500 roentgens increased the yield by 37 percent! Collecting 100 or 137 kg of radish is a significant difference. And this is from the same amount of seeds, on the same lands and with the same care. And the cost of irradiation is extremely low.
In other varieties of radish - "Ruby", "Pink with a white tip", "Sax" - the yield increased with irradiation at a dose of 1000 roentgens. And the irradiated "Sax" was also juicier and ripened earlier than usual by 5-6 days Pre-sowing irradiation of seeds "Rubin" not only increased the yield of root crops, but also increased the content of vitamin C in them. With the help of ionizing radiation, the content of vitamin A in root crops can also be increased. to the control increased by 26 percent, and the stock of carotene - a plant pigment that is converted into vitamin A in the human body - by 56.
What about corn? Irradiation of seeds at a dose of 500 roentgens increased the yield of green mass up to 28 percent
The stimulating effect of pre-sowing seed irradiation has been proven for cucumbers, tomatoes, beets, cabbage, salut, potatoes, cotton, rye, barley...
Scientists have noticed one feature. The dose of ionizing radiation that causes the stimulation effect is different not only for different plant species, but even for different varieties of the same species. Moreover, it turned out to be not the same for the same variety sown in different geographical areas.
Thus, the stimulating dose of irradiation for cucumbers of the Nezhinsky variety, sown in the Moscow region, is 300 roentgens, and to obtain the same result in Azerbaijan, a dose of about 2000-4000 roentgens was needed.
Let's take corn seeds. Lots of seeds. We irradiate them under the same conditions with a dose of gamma rays that causes a stimulating effect. We will divide them into four equal groups - 1000 pieces in each. We will sow one group immediately after irradiation, the second - in a week, the third - in two, the fourth - in a month. Now let's wait patiently. The seeds have sprouted, the plants have begun to develop. But what is it? Plants sown immediately after irradiation develop faster than others. In seeds that were sown a week after irradiation, the stimulation effect was less pronounced. In seeds sown 2 weeks after irradiation, development acceleration was almost not observed. Seeds aged after irradiation for a month germinated, but did not have a stimulating effect. So, while storing some mysterious substance, some kind of stimulant slowly disappeared.
What's the matter?
We are entering an area where facts are still friends with assumptions, where much has not yet been explored. It has been established that after irradiation, very active fragments of molecules, called Opi radicals, are formed in the seeds, capable of entering into reactions unusual for a healthy organism. And it turned out that after irradiation of seeds, the number of radicals gradually decreases with time. A few days pass, and the radicals disappear completely. The higher the temperature and humidity at which the seeds are stored, the faster the radicals disappear.
What happens when the seeds fall into moist, sun-warmed soil? The nutrients contained in the seeds begin to pass into a soluble form and are transported to the embryo. In the so-called aleurone layer of the seed, oxidative processes are activated, and the production of energy-rich compounds begins. The embryo awakens, its cells swell and begin to divide. The processes of growth and development of seedlings begin. Cells begin to divide, and they need building material. The activity of many enzymes increases significantly as a result of irradiation. And when seeds are irradiated, oxidative processes begin to proceed much more intensively. And this leads to faster development and acceleration of seed germination, to their germination. Plants become more powerful.
Not so long ago, an article was published in the Courier magazine, which is published by the UN. It said that one in three farmers in Africa actually worked for birds, rodents, pests and microparasites.
Naturally, it is difficult to vouch for the accuracy of these figures, but the fact that the losses from pests are huge is a fact.
Experts have calculated agricultural pests destroy so much grain in a year that they could feed 100 million people.
How can ionizing radiation help agriculture in pest control?
You already know: different types of plants have different radiosensitivities. Some are quite high. Insects are generally highly radioresistant. Among them there are even peculiar champions of radio stability. For example, scorpions. But the eggs and larvae of the insects were found to be more radiosensitive. And reproducing insect cells are also more sensitive to radiation.
The scheme for combating insect pests is simple. Grain is passed through a conveyor through a hopper charged with a radioactive isotope. For a certain period of time, it receives the dose of ionizing radiation necessary for the death of pests. Such grain, of course, is not used as planting material. But it is completely harmless for human nutrition. After irradiation the grain enters the storage - a dangerous pest no longer threatens it. The same methods can be used to deal with pests of dry fruits - insects and their larvae, irradiating "future compotes" with gamma rays at a dose of up to 50,000 roentgens. And in Canada, they proposed a method of radiation control of salmonella, contaminating egg powder Do you know about the sterile male method? Scientists have developed it relatively recently. Insects exposed to ponting radiation during a certain period of development are unable to produce offspring. "Sterile males" mate with normal females. However, the female does not bring offspring. The more males will be sterilized, the more opportunities that females will not give offspring. If there are many sterilized insects for several generations, then the offspring will decrease sharply. In some countries, a dangerous pest lives - the so-called blowfly. It lays its eggs in brines of warm-blooded animals Eggs develop into larvae that cause disease and even death of livestock, wild animals and game The blowfly causes great harm to the economy And then they decided to try the method of radiation sterilization on the blowfly They built a “fly” factory, where they bred and sterilized flies Sterilized insects were released onto the contaminated area The result was quick The disease and mortality of livestock decreased dramatically The cost of the "fly" factory not only paid off in the first year, but also brought an equal profit in terms of the amount of costs. In the US, on the island of Kurakoo, an area of 435 square kilometers, about 2,000 sterile male blowflies were released per square kilometer. On the island, blowflies are practically destroyed.
The idea of canning food was raised a long time ago. Food was canned by the ancient Egyptians and ipki. Probably the most ancient way to preserve food is to dry it in the sun. Over time, the methods of canning have changed. Today, there is a refrigerator in almost any city apartment. But the most modern way to preserve food is to preserve them using penetrating radiation. If, for example, fresh meat is irradiated with gamma rays at a dose of 100,000 reptiles, then its snoring period in the warehouse is five times longer. qualities With the help of radiation, the shelf life of fresh fish is extended. Irradiated fish in refrigerators retains their taste qualities for up to 35 days, and without radiation treatment under the same storage conditions - 7 - 10 days.
Now they are looking for a way to preserve caviar, milk, fruits and seafood - crabs, oysters, shrimps using gamma rays.
Irradiation of berries and fruits gives good results. Irradiated strawberries stored in a refrigerator at a temperature of +4 degrees did not lose their freshness or aroma for a long time. Even experienced tasters and experts could not determine which of the berries were irradiated in “preserving” doses. ? They have excellent taste qualities And they can be grown artificially throughout the year But during storage, mushrooms quickly deteriorate, lose their freshness and taste, dry out and their hat unfolds, like old mushrooms Irradiated champignons during long-term storage looked like they had just been brought from a greenhouse - the aging of mushrooms was sharply slowed down, their hats were abruptly twisted, like those of young mushrooms.
Recently, a report appeared in the press about the beam copying of colors. The famous Dutch tulips, irradiated in a certain dose, placed in a bag inflated with carbon dioxide, are easy to transport and can be stored for a long time. It seemed that they had just been plucked from the garden, their petals were so fresh.
It is especially beneficial to increase the shelf life of vegetables with the help of radiation.
Potatoes have one serious drawback: during storage, they germinate, the tubers shrivel and lose their taste. Many scientists began to work on the problem of radiation preservation of potatoes in various research institutes of our country. Numerous experiments have shown that irradiation of tubers at a dose of 10,000 roentgens sharply slows down or stops the spring germination of potatoes and does not lower its resistance to diseases. The palatability of irradiated potatoes does not deteriorate. Experienced tasters did not find any changes in dishes prepared from such potatoes.
The problem of radiation conservation is being intensively developed all over the world. And this is natural. It brings too obvious economic benefits. Some methods of radiation preservation have already been approved for practical use. Others have not yet left the walls of laboratories. And most importantly, many years of experiments are underway, which should prove that irradiated products are harmless to humans.
Plants are easier to experiment with than animals. Working with the irradiation of seeds, it is possible to perform experiments on many thousands of biological objects at once. And that is why statistics helps a scientist significantly. Yes, and economically such an experience is much more profitable.
Has ionizing radiation been used for practical purposes in animal husbandry?
Animals are much more sensitive to the action of penetrating radiation than plants. In our country, such an experiment was carried out at one of the modern poultry farms. For several hours, during the incubation process, chicken eggs were irradiated at a dose of 1-2 roentgens. Such insignificant doses of radiation had a stimulating effect: the number of hatched chickens increased, and hens from irradiated eggs had greater egg production.
Chickens are "lucky" or is the stimulating effect of small doses of ionizing radiation a general pattern?
Probably, general patterns are also hidden here. In any case, doctors all over the world have long recognized the healing effect of radon baths for humans.
So, the ionizing radiation of radioactive isotopes can be reasonably used by humans in agriculture as well. But the inquisitive reader has probably already noticed that it was about external sources of penetrating rays. As a rule, about gamma rays emitted by radioactive cobalt. But there are a huge number of radioactive isotopes that emit, for example, "soft" beta rays, the energy of which is low. Radioactive carbon C "and radioactive sulfur B3®, biologically the most important elements, have just such a "soft" radiation. The energy of the penetrating radiation of another biologically important isotope - radioactive phosphorus P3! is much higher, but it is also "softer" compared to " hard" gamma rays of cobalt Co0.
The possibilities of using such "labeled" atoms in the national economy are also great. Let's give examples.
To defeat the enemy, you need to know him. In order to successfully deal with dangerous pests of agriculture, with harmful insects, it is necessary to study their life well.
Scientists labeled with radioactive phosphorus such dangerous insects as locusts, malarial mosquitoes, and fruit flies. This method was used to determine the flight speed of the locust and the range of its distribution from the main breeding centers; found out the length of flights of malarial mosquitoes. The fruit fly turned out to be a relative homebody. It was labeled with radioactive phosphorus and released in an orange grove. Under favorable conditions, fruit flies did not move more than a few hundred meters from their habitat.
The information obtained made it possible to outline the location of the barrier zones and develop a system of defense and control of these insects.
Insecticides - poisons for insects, one of the modern methods of dealing with them. Let us introduce a radioactive label into these chemical compounds. The indicator immediately allows you to answer a number of important questions. How do these compounds behave in the body of insects, why are they poisonous to them? How to make them selective in action - not harmful to humans, plants and beneficial insects? Do poisons get into agricultural products? When do poisons lose their toxicity?
Experiments were made on our oldest friends - bees. For example, they fed a worker bee with radioactive phosphorus, and it became labeled. A counter of radioactive particles was placed in the hive And now it was possible to establish how many times a day a worker bee flies to work, what is its working day and what is the speed of flight Or did it differently Sugar-sweetened solutions with radioactive phosphorus mixed with them were placed on some field Arrivals bees, of course, rushed at it. And then it was possible to determine exactly which fields are most popular with bees. And hence the practical solutions that will help increase the production of tireless workers.
Radioactive isotopes are used in all research in the biochemistry and physiology of insects. The significance of these works is clear. By studying, for example, the activity of hormones and enzymes that control the development and behavior of beneficial insects, it will be possible to use insects in the interests of man.
Scientists were amazed when they learned how fast certain biochemical processes occur in plants.
Several leaves of a plant were placed in a plexiglass box, a certain amount of carbon dioxide radioactive in terms of carbon was injected into it, and the plant was left in sunlight. As a result of photosynthesis, carbon dioxide was assimilated, passed into the composition of organic substances and transported to various parts of the plant. Samples were taken at regular intervals and measured. radioactivity And it turned out that the speed of movement of newly synthesized compounds with an upward current is very significant: dpem in sunlight - 50-100 centimeters per minute. Previously, it was believed that all carbon in organic substances is formed by steppe from carbon dioxide of the air, although it is there hundredths of a procept Only relatively recently, with the help of labeled atoms, it was possible to prove that carbon dioxide and carbonic acid salts contained in the soil are intense.
Radioactive phosphorus can be used to mark insects and plants.
used by the plant. They are actively transported from roots to leaves. There, as a result of photosynthesis, carbohydrates are formed from them and organic substances are synthesized. And from here a practically important conclusion followed: to increase the yield, it is necessary to enrich the soil with carbon dioxide - to introduce salts of carbonic acid into the soil. You can also add so-called green fertilizers to the soil. For example, plow in perennial grasses. After about 20-30 days, the release of carbon dioxide begins, which continues all summer.
So the use of the method of radioactive tracers proved to be useful for the science of plant fertilizers.
What and how is it more profitable to feed the plants? At what time? What form of fertilizer should be applied? How are they affected by climatic conditions? How are they transported in plants and where are they absorbed?
Phosphorus-labeled superphosphate, hydroxylapatite, and other fertilizers were applied to the soil. And it turned out that 2.5 months after planting, corn absorbed phosphorus best from tricalcium phosphate, worse from superphosphate, and even worse from hydroxyapatite. It was found that cotton especially needs to be fed with phosphorus at the age of 10-20 days and during flowering.
With the help of labeled atoms, the role of microelements in the life of plants - cobalt, manganese, zinc, copper - was determined. It is enough, for example, to add 1-3 kilograms of boron per hectare of arable land to the soil, and the yield of clover will increase dramatically. Manganese increases the yield of sugar beet, copper sulphate - the yield of cereals on peat soils.
Once, at a lecture on radiation biochemistry, a student of the Faculty of Biology at Moscow University approached me. She complained that in our time the impossibility of a miracle had been proved. “There was some hope,” she said, “when reports appeared in the press about the existence of a Bigfoot or the assumption that it was not the Tunguska meteorite that fell to Earth, but a spaceship from unknown planets of an unearthly civilization. So you don't! Meticulous scientists quickly proved that this could not be.
But didn't researchers find a small miracle when they found that individual trees in a forest can exchange nutrients with each other through fused roots? In an oak grove, radioactive potassium bromide introduced into a tree was detected in 3 days in five adjacent oaks!
Chemical compounds labeled with radioactive carbon, phosphorus, and sulfur are especially often used. And of course, microelements and compounds such as potassium, sodium, iron ... But you need to have a good understanding of the research problem in order to choose the right radioisotope. For example, the half-life of radioactive carbon C "is about 6000 years. This radioisotope is too "young" to study geological processes , but it is indispensable for the study of metabolic processes in animals.
Using radioactive carbon, you can find out what nutritional conditions are necessary to achieve maximum productivity of animals or how nutritious feed is digested and what needs to be introduced into the diet of cows in order to increase milk yield.
Without a good theory, there can be no good practice. The possibilities of the method of radioactive isotopes for solving the most complex theoretical issues of biochemistry, physiology, and biophysics are limitless. Within one working day, a scientist will not have time to read even the headlines of articles and studies that describe the use of radioactive isotopes for various Biological Targets Even experts are often surprised by studies that use labeled atoms.
Sometimes complex biological problems are solved simply Sometimes it’s the other way around: a seemingly simple biological phenomenon is deciphered through many years of painstaking work
For example, from what constituent, simplest parts is cow's milk formed and in what tissues?
The question sounds simple, but it took the efforts of many dozens of scientists over many years to answer it.
Three quarters of a century ago, only a few people knew about the existence of radioactive isotopes. Today, "useful radiation" has become the property of millions of people. Albert Einstein said: "The phenomena of radioactivity are the most revolutionary force in technological progress ever since prehistoric man discovered fire."
Evgeny Romantsev. "Born of the Atom"
Home > Teaching aid2.2 Effect of ionizing radiation on plants
In general, plants are more resistant to radiation exposure than birds and mammals. Irradiation in small doses can stimulate the vital activity of plants - Figure 3 - seed germination, intensity of root growth, accumulation of green mass, etc. It should be noted that the dose curve shown in this figure is certainly repeated in experiments with respect to a wide variety of plant properties for doses of radiation exposure that cause inhibition of processes. With regard to stimulation, the dose characteristics of the processes are not so obvious. In many cases, the manifestation of stimulation on living objects is not observed.
Figure 3 - Dependence of the number of sprouted eyes of a potato variety on the dose of radiation
Large doses (200 - 400 Gy) cause a decrease in plant survival, the appearance of deformities, mutations, and the appearance of tumors. Disturbances in the growth and development of plants during irradiation are largely associated with changes in metabolism and the appearance of primary radiotoxins, which stimulate vital activity in small quantities, and suppress and disrupt it in large quantities. Thus, washing irradiated seeds within a day after irradiation reduces the inhibitory effect by 50-70%.
In plants, radiation sickness occurs under the influence of various types of ionizing radiation. The most dangerous are alpha particles and neutrons that disrupt nucleic, carbohydrate and fat metabolism in plants. Roots and young tissues are very sensitive to radiation. A common symptom of radiation sickness is growth retardation. For example, in young plants of wheat, beans, corn, and others, growth retardation is observed 20–30 hours after irradiation with a dose of more than 4 Gy. At the same time, various researchers have shown that irradiation of air-dry seeds of many crops with doses of 3-15 Gy not only does not lead to inhibition of plant growth and development, but, on the contrary, contributes to the acceleration of many biochemical processes. This was expressed in the acceleration of development and increase in productivity.
Species, varietal and individual intra-varietal differences in the radiosensitivity of plants have been established. For example, the symptoms of radiation sickness in tradescantia occur when it is irradiated with a dose of 40 r, in gladiolus - 6000 r. The lethal dose of irradiation for most higher plants is 2000-3000 r (absorbed dose of the order of 20-30 Gy), and for lower plants, such as yeast, 30,000 r (300 Gy). Radiation sickness also increases the susceptibility of plants to infectious diseases. Affected plants should not be used for food and livestock feed, as they can cause radiation sickness in humans and animals. Methods for protecting plants from radiation sickness have not been sufficiently developed.
2.3 Effect of ionizing radiation on invertebrates
The radiosensitivity of invertebrates varies considerably: the semi-lethal dose in some ascidians, coelenterates, arthropods, and nematodes ranges from 30 to 50 Gy. In mollusks, it is in the range of 120-200 Gy, in amoebas this value reaches 1000 Gy, and in ciliates, resistance is close to that of microorganisms - LD 50 is in the range of 3000-7000 Gy.
Radiosensitivity depends both on the totality of the properties of the organism and the state of the environment, and on the period of ontogenesis. So in Drosophila, the semi-lethal dose in the adult stage is 950 Gy, in the pupal stage 20-65 Gy, the sensitivity of eggs, depending on time, varies from 2 to 8 Gy, and in the larval stage it is 100-250 Gy.
2.4 Effect of ionizing radiation on vertebrates
The sensitivity of vertebrates to radiation exposure is much higher than that of the previous groups of organisms. The most radio-resistant snakes, in which LD 50 is in the range from 80 to 200 Gy, in newts and pigeons it corresponds to 25-30 Gy, in turtles - 15-20 Gy, in chickens - 10-15 Gy, for cyprinids - 5 -20 Gr, for rodents 5-9 Gr. Mammals are even less resistant to radiation. The semi-lethal dose for dogs is 2.5-4 Gy, and for monkeys 2-5.5 Gy. Animals have radiation sickness. most studied in domesticated mammals and birds. Distinguish between acute and chronic radiation sickness. Acute occurs with a single total exposure to exposure doses: 1.5-2.0 Gy (mild), 2.0-4.0 Gy (medium), 4.0-6.0 Gy (severe) and over 6.0 Gr (extremely heavy). Depending on the severity of the course of radiation sickness. in animals, depression, loss of appetite, vomiting (in pigs), thirst, diarrhea (may be with mucus, blood), a short-term increase in body temperature, hair loss (especially in sheep), hemorrhages on the mucous membranes, weakening of cardiac activity, lymphopenia and leukopenia. With an extremely severe course - unsteadiness of gait, muscle cramps, diarrhea and death. Recovery is possible with mild and moderate course of the disease. Chronic radiation sickness. develops with prolonged exposure to small doses of general gamma radiation or radioactive substances that have entered the body. It is accompanied by a gradual weakening of cardiac activity, dysfunction of the endocrine glands, exhaustion, weakening of resistance to infectious diseases. The treatment is preceded by the withdrawal of animals from the contaminated area, the removal of radioactive substances from the outer covers with water, detergents and other means. At the onset of the disease, a blood transfusion or blood substitutes, intravenous administration of a 25-40% glucose solution with ascorbic acid is recommended. In case of infection through the digestive tract, adsorbents are used (an aqueous mixture of bone meal or barium sulfate with potassium iodide), in case of damage through the lungs, expectorants.
With internal damage to animals, radioactive substances are released from the body, polluting the external environment, and with food (milk, meat, eggs) they can enter the human body. Products from animals that have undergone radiation damage are not used as food or feed for animals, as they can cause radiation sickness in them.
2.5 The effect of ionizing radiation on humans
The large material accumulated to date, obtained in experiments on animals, as well as on the basis of generalization of long-term data on the state of health of radiologists, radiologists and other persons who were exposed to ionizing radiation, shows that with a single uniform gamma irradiation of the whole body, consequences occur, summarized in Table 1
| Dose, Gy * | Effects |
| death occurs within a few hours or days due to damage to the central nervous system. |
|
| death occurs in one to two weeks due to internal hemorrhages. |
|
| 50% of those exposed die within one to two months due to damage to bone marrow cells. |
|
| disability. Possible death. |
|
| lower level of development of radiation sickness. |
|
| short-term minor changes in the composition of the blood. |
|
| irradiation during fluoroscopy of the stomach (single). |
|
| permissible emergency exposure of personnel (single). |
|
| permissible emergency exposure of the population (single). |
|
| allowable exposure of personnel under normal conditions per year. |
|
| allowable exposure of the population under normal conditions per year. |
|
| the average annual equivalent dose due to all radiation sources. |
Radiation sickness, a disease arising from exposure to various types of ionizing radiation. Man, animals, microorganisms and plants are constantly exposed from the outside to the action of gamma radiation from the earth's crust, cosmic rays and are irradiated from the inside by radioactive substances in the human body in negligible amounts (46 K, 226 Ra, 222 Rn, 14 C, etc.). The development of radiation sickness. occurs only when the total dose of radiation begins to exceed the natural radioactive background. The ability of radiation to cause radiation sickness depends on the biological effect of ionizing radiation; the greater the absorbed dose of radiation, the more pronounced the damaging effect of radiation.
In humans, radiation sickness can be caused by external radiation, when its source is outside the body, and internal - when radioactive substances enter the body with inhaled air, through the gastrointestinal tract or skin. Radiation sickness can develop with relatively uniform irradiation of the whole body, any organ or part of the body. There are acute radiation sickness arising from a single general exposure in relatively large doses (hundreds of rads), and a chronic form, which may be the result of acute radiation sickness or chronic exposure to small doses (units of rads).
The general clinical manifestations of radiation sickness depend mainly on the total dose received. With a single total exposure to a dose of up to 100 r (of the order of 1 Gy), relatively slight changes occur, which can be considered as a state of the so-called pre-illness. Doses above 100 r cause various forms of radiation sickness (bone marrow, intestinal) of varying severity, in which the main manifestations and outcome of radiation sickness depend mainly on the degree of damage to the hematopoietic organs.
Doses of a single total exposure over 600 r (more than 6 Gy) are considered absolutely lethal; death occurs within 1 to 2 months after irradiation. In the most typical form of acute radiation sickness, at first, after a few minutes or hours, those who received a dose of more than 200 r experience primary reactions (nausea, vomiting, general weakness). After 3-4 days, the symptoms subside, a period of imaginary well-being begins. However, a thorough clinical examination reveals the further development of the disease. This period lasts from 14-15 days to 4-5 weeks.
Subsequently, the general condition worsens, weakness increases, hemorrhages appear, body temperature rises. The number of leukocytes in the peripheral blood after a short-term increase progressively decreases, falling (due to damage to the hematopoietic organs) to extremely low numbers (radiation leukopenia), which predisposes to the development of sepsis and hemorrhages. The duration of this period is 2-3 weeks.
There are other forms of radiation sickness. For example, with total irradiation in doses from 1000 to 5000 r (10-50 Gy), an intestinal form of radiation sickness develops, characterized mainly by intestinal damage, leading to impaired water-salt metabolism (from profuse diarrhea), and impaired blood circulation. A person with this form usually dies within the first day, bypassing the usual phases of the development of radiation sickness. After total irradiation in doses of more than 5000 r (more than 50 Gy), death occurs in 1-3 days or even at the time of irradiation itself from damage to brain tissues (this form of radiation sickness is called cerebral). Other forms of radiation sickness in humans and animals are mainly determined by the place of exposure.
Features of the course and the degree of disturbances in radiation sickness depend on individual and age sensitivity; children and the elderly are less resistant to radiation, so severe injuries can occur in them from lower doses of radiation. During the period of embryonic development, body tissues are especially sensitive to the effects of radiation, so exposure of pregnant women (for example, the use of radiation therapy) is undesirable even in small doses.
The process of recovery of the body after irradiation in moderate doses occurs quickly. In mild forms of radiation sickness, pronounced clinical manifestations may be absent. In more severe forms of radiation sickness, the period of complete recovery is sometimes delayed up to a year or more. As a distant manifestation of radiation sickness in women, infertility is noted, in men - the absence of spermatozoa; these changes are often temporary. After many months and even years, after irradiation, clouding of the lens sometimes develops (the so-called radiation cataract). After acute radiation sickness, persistent neurotic manifestations, focal circulatory disorders sometimes remain; it is possible to develop sclerotic changes, malignant neoplasms, leukemia, the appearance of malformations in the offspring, hereditary diseases.
The characteristic features of chronic radiation sickness are the duration and undulation of its course. This is due to manifestations of damage, on the one hand, and restorative and adaptive reactions, on the other. With a predominant lesion of one or another organ or tissue, there is a discrepancy between the depth of damage to the damaged structures and the signs of general reactions of the body that are poorly expressed or appear late.
In the early stages, the main clinical manifestations are a variety of disorders of the nervous regulation of the functions of internal organs and, first of all, the cardiovascular system. There may be changes in the enzymatic activity and secretory-motor function of the gastrointestinal tract; violations of the physiological regeneration of hematopoiesis cause the development of leukopenia. With continued exposure and progression of the disease, all manifestations are aggravated.
Treatment of acute radiation sickness is aimed at normalizing the hematopoietic organs (bone marrow transplantation, blood transfusion, administration of nucleic acids, hematopoietic stimulants), fighting infection (antibiotics), preventing the occurrence of hemorrhages (vitamins), reducing intoxication (bleeding, blood substitution), affecting nervous system, etc. In chronic radiation sickness. prescribe a diet rich in proteins and vitamins, a long stay in the fresh air, physiotherapy exercises; symptomatic agents (cardiac, neurotropic, normalizing the function of the gastrointestinal tract, etc.). In violation of hematopoiesis - drugs that stimulate it.
Legislated norms for maximum allowable doses and concentrations of radioisotopes for various industries and professional groups are established based on total exposure at a dose of not more than 50 mSv / year (5 rad / year) and guarantee the safety of working with these substances. Exposure hazard may arise in case of violation of labor protection rules or in emergency situations, in wartime conditions (the use of atomic weapons by the enemy).
Nuclear explosions sharply increase the pollution of the environment with radioactive fission products, as a result of which the amount of radioactive iodine (111 I), strontium (90 Sr), cesium (137 Cs), carbon (14 C), plutonium (239 Pu) and others. There is a threat of radiation hazardous to health and an increase in the number of hereditary diseases. In such cases, protection from ionizing radiation is of decisive importance for the prevention of the development of radiation sickness.
2.5.1 Doses to humans from various sources Radiation impacts on humans are very diverse, they can be, depending on the location of the sources relative to the organism exposed to radiation: - external; - internal. Depending on the origin: - natural; - technogenic (anthropogenic). Depending on the physical condition nuclides: - gaseous; - liquid; - solid. Depending on the activity: - highly active; - low active. Depending on the location of the source of ionizing radiation: - terrestrial; - space. depending on where you live and work. Thus, residents of mountains and landscapes with an increased radiation background can receive doses several times higher than the annual loads of inhabitants of the plains. Pilots and climbers also receive additional radiation exposure. Permissible limits are given in paragraph 10 - radiation safety standards, and on the diagram - figure 4, the doses received by a person from various sources are shown. The diagram shows the values of natural background exposure, average doses received from TV screens and computers, the value of the permissible exposure, doses received from x-rays of the teeth and stomach, and, finally, the planned dose for emergency exposure.
The normalized value is also the content of some radionuclides of technogenic origin in food products. First of all, this applies to the radionuclides of cesium-137 and strontium-90. The diagram - Figure 5 - shows the content of K-40 in food products in comparison with the allowable content of Cs-137 and Sr-90. As follows from the diagram, in many food products the content of the natural radionuclide K 40 is significant compared to the allowable content of Cs -137 and Sr-90. In the soil of territories with high anthropogenic pollution with cesium and strontium, the content of potassium-40, as a rule, is many times higher than the average total values of Cs 137 and Sr 90 . The contribution of radioactive potassium is 12.3% of the entire value of the average background level of natural exposure of the human bone marrow and accounts for the bulk of internal exposure. Natural irradiation of the human bone marrow, one of the most sensitive organs, consists of exposure to cosmic sources, the total value of which reaches 50 μR / year, the value of lithospheric and atmospheric sources is also 50 μR / year.
Of the elements in the body, K 40 plays a significant role, which gives 15 μR / year, other elements that are inside the human body make a smaller contribution - Figure 6 - radon - 222 adsorbed in the blood gives 3 μR / year, carbon - 14 - 1 .6 μR / year, radon - 226 and radon -228 and their daughter decay products also give a total of 1.6 μR / year, and, finally, polonium - 210 and daughter decay products give 0.4 μR / year.
2.6 Comparative values of radiosensitivity
Table 2 - Radiosensitivity of different groups of organisms | An object | LD 50 , Gr |
| bacteria | |
| higher plants | |
| Invertebrates | |
| Vertebrates |
As can be seen from the table, the range of resistance to radiation in wildlife is quite wide. Microorganisms are the most resistant to the action of ionizing radiation - the doses that can cause their death are hundreds and thousands of grays. For invertebrates, the range of lethal doses is usually an order of magnitude lower than these values, and for vertebrates they are tens of grays, here mammals are most sensitive to radiation exposure. Based on the data in Table 2, we can conclude that as the biological organization of objects becomes more complex, their resistance to radiation decreases sharply.
Usually, animals irradiated at a dose of 5 - 10 Gy live on average (with some exceptions) from several days to several weeks. Radiation syndrome in this range of radiation doses is called "bone marrow" or "hematopoietic", because the defeat of the hematopoietic system of the body, primarily the bone marrow, is of decisive importance in its outcome. As a result of deep inhibition of cell division processes, bone marrow is depleted. The outcome of radiation sickness is significantly affected by the ability of hematopoietic organs to recover, which depends on the number of preserved stem cells.
In the dose range from 10 to 100 Gy, the average lifespan of mammals is practically independent of the absorbed dose and averages 3.5 days. The effect of the independence of the average life expectancy from the magnitude of the radiation dose was called the "3.5-day effect", and the emerging radiation syndrome was called "gastrointestinal". The lethal outcome of this syndrome is associated with damage to the intestinal mucosa and stomach, high sensitivity to radiation of rapidly dividing epithelial cells, and exposure of the villi.
Irradiation in doses exceeding 100 Gy leads to the death of mammals, which occurs in the first few days or even a few hours. In dying animals, there are clear signs of damage to the central nervous system, so this radiation syndrome is called "cerebral". There is a sharp suppression of the vital activity of nerve cells, the reaction of which to radiation fundamentally differs from the reaction of the bone marrow and intestines by the absence of cell losses.
If the absorbed dose reaches 1000 Gy or more, the animals die immediately "under the beam". The mechanism of such damage may be related to the fact that massive structural damage to macromolecules occurs. Sometimes radiation syndrome caused by exposure to such high doses of ionizing radiation is called molecular death.
In the body's responses to the action of ionizing radiation, it is conditionally possible to distinguish three successively developing stages in time; physical reactions, biophysical processes and general biological changes. The physical stage - energy absorption, ionization and excitation of atoms and molecules, the formation of radicals - occurs within micro- and milliseconds. Biophysical processes - intra- and intermolecular energy transfer, interaction of radicals with each other and with intact molecules, intramolecular changes - occur within seconds - milliseconds. General biological changes in the cell and body - the formation of stable altered molecules, violation of the genetic code, transcription and translation, biochemical, physiological and morphological changes in cells and tissues, sometimes ending in the death of the body, can occur within minutes - days or stretch for years.
It has been established that different organs and tissues differ greatly in their sensitivity to ionizing radiation, as well as in their role in radiation pathology and the final outcome of the disease. According to morphological changes, their radiosensitivity is located (according to the degree of decreasing sensitivity) in the following sequence:
Organs of hematopoiesis;
sex glands;
Mucous membranes, salivary, sweat and sebaceous glands, hair papillae, epidermis;
Gastrointestinal tract;
Respiratory system;
Endocrine glands (adrenals, pituitary, thyroid, pancreatic islets, parathyroid);
excretory organs;
Muscular and connective tissue;
Somatic bone and cartilage tissue;
nervous tissue.
Hematopoietic organs are the most radiosensitive, damage to the bone marrow, thymus, spleen, and lymph nodes is one of the most important manifestations of acute radiation sickness. Significant morphological and functional disorders are observed in all hematopoietic organs, and it is possible to detect changes in the blood system soon after exposure to radiation and even at relatively low doses of radiation.
Usually the process of cellular devastation is divided into three stages. The first, lasting about 3 hours, is characterized by a relative constancy of the content of cells in the hematopoietic tissues. The second stage covers the time interval from 3 to 7 hours after irradiation, it is characterized by a sharp and deep devastation of the bone marrow and lymphoid tissues (the number of cells in the bone marrow tissue can decrease by more than half). In the third stage, the rate of cell devastation slows down and a further decrease in the number of cells occurs in the bone marrow as a result of reproductive death, as well as the ongoing differentiation of some cells and their migration into the blood. The duration of the third stage is proportional to the radiation dose.
Salt tolerance
Plants resistant to salinity are called halophytes (from Greek galos - salt, Phyton - plant). They differ from glycophytes - plants of non-saline water bodies and soils - in a number of anatomical and metabolic features. In glycophytes, salinity reduces cell growth by elongation, disrupts nitrogen metabolism, and accumulates toxic ammonia.
All halophytes are divided into three groups:
1. True halophytes (euhalophytes) are the most resistant plants that accumulate significant amounts of salts in vacuoles. Therefore, they have a large suction power, allowing them to absorb water from highly saline soil. Plants of this group are characterized by the fleshiness of the leaves, which disappears when they are grown on non-saline soils.
2. Salt-producing halophytes (crinohalophytes), absorbing salts, do not accumulate them inside the tissues, but remove them from the cells to the surface of the leaves with the help of secretory glands. The separation of salts by glands is carried out with the help of ion pumps and is accompanied by the transport of large amounts of water. The salt is removed with the falling leaves. In some plants, getting rid of excess salts occurs without the absorption of large amounts of water, since the salt is released into the vacuole of the head cell of the leaf hair, followed by its breaking off and restoration.
3. Salt-resistant halophytes (glycohalophytes) grow on less saline soils. The high osmotic pressure in their cells is maintained by the products of photosynthesis, and the cells are not permeable to salts.
Salt tolerance of plants increases after presowing seed hardening. The seeds are soaked for one hour in a 3% NaCl solution, followed by washing with water for 1.5 hours. This technique increases the resistance of plants to chloride salinization. For hardening to sulfate salinization, the seeds are soaked for a day in a 0.2% solution of magnesium sulfate.
There are direct and indirect effects of radiation on living organisms. The direct action of radiation energy on a molecule transforms it into an excited or ionized state. Damage to the DNA structure is especially dangerous: breaks in sugar-phosphate bonds, deamination of nitrogenous bases, and the formation of dimers of pyrimidine bases. The indirect effect of radiation is damage to molecules, membranes, cell organelles caused by the products of water radiolysis. A charged particle of radiation, interacting with a water molecule, causes its ionization. Water ions during a lifetime of 10 -15 - 10 -10 sec are able to form chemically active free radicals and peroxides. These strong oxidizing agents during the lifetime of 10 -6 - 10 -5 sec can damage nucleic acids, enzyme proteins, membrane lipids. Initial damage is enhanced by the accumulation of errors in the processes of DNA replication, RNA and protein synthesis.
The resistance of plants to the action of radiation is determined by the following factors:
1. The constant presence of enzymatic DNA repair systems. They find the damaged area, destroy it and restore the integrity of the DNA molecule.
2. The presence in the cells of substances - radioprotectors (sulfhydryl compounds, ascorbic acid, catalase, peroxidase, polyphenol oxidase). They eliminate free radicals and peroxides generated by irradiation.
3. Restoration at the level of the organism is provided in plants by: a) the heterogeneity of the population of dividing meristem cells, which contain cells at different phases of the mitotic cycle with unequal radioresistance, b) the presence of resting cells in the apical meristems, which begin to divide when the division of cells of the main meristem stops, c) the presence of dormant buds, which, after the death of the apical meristems, begin to function actively and restore damage.
After radioactive fallout, some of it directly enters the plants, affecting them in one way or another in the near future, and some then enters through the root system, causing one effect or another. Let us consider some reactions of plants to radiation damage using the example of forest woody plants.
Kidneys. One of the characteristic signs of radiation damage to woody plants is damage and death of the growth buds of the apical and lateral shoots. For example, at an absorbed dose of 20-40 Gy, not all kidneys dry out. Some of them give an increase in shoots in the first growing season after irradiation. Shoots are strongly shortened and do not have needles or have rare single needles instead of bunches.
Leaves and needles. The damage to the leaves and needles of woody plants during irradiation is one of the most important radiation effects, since it is associated with the damage and death of trees. For example, with acute γ-irradiation, after 3 months at doses of 100-200 Gy, pine damage begins. 15-20 days after irradiation, the color of the needles from dark green becomes orange-yellow. Then this color appears on the entire crown, and the trees dry out. In the range of absorbed doses of 70-100 Gy, external signs of pine damage appear after 6 months (needles turn yellow). When irradiated with 5-40 Gy, yellowing of individual bunches of needles on annual shoots is observed. At doses of 10-60 Gy, two-year-old needles turn yellow in the upper part of the crowns of pine trees for 1/2-1/4 of the shoot length. At doses of 60-100 Gy, two-year-old needles die completely.
Cambium. Even with partial radiation damage to the cambium, the trees become windfall and windbreak. In the experiment, most of the trees were broken by the wind within two years after irradiation.
Growth. The inhibition of the growth of pine shoots in autumn is observed at an absorbed dose of 10-30 Gy. In the first year after irradiation, the shoots were 2-3 times shorter, in the second growing season they were significantly smaller, and in the third they disappeared. A significant decrease in pine productivity is observed at an absorbed dose of more than 5 Gy and is especially noticeable in the second and subsequent periods of vegetation after irradiation. At an absorbed dose of more than 25 Gy, productivity drops to zero in 2 years Phenology. The reaction to irradiation in hardwoods is manifested in shifts in the onset of the main phenophases: a slowdown in leaf blooming in spring and earlier leaf fall. There are practically no significant differences in the passage of spring phenophases in birch and aspen in irradiated and non-irradiated plantations, and in autumn on irradiated aspen and birch leaves turn yellow and fall off earlier. On pines at absorbed doses above 5 Gy, early fall of needles of older ages is noted. At doses of 100-200 Gy, the delay in leaf blooming in trees is 7-9 days, the next year - 4-5 days. After 5 years from the moment of pollution, the phenological shift decreases, and after 7 years it disappears.
Effects of radiation on animals.
In the impact of radiation, a new ecological factor for animal populations, 2 periods are distinguished:
1. The population was exposed for the first time to conditions of severe radioactive contamination. There is a sharp impact on the population: the age, sex and spatial structures of the population change: mortality increases and decreases
2. The population lived in conditions of radioactive contamination for several years, for which gave a number of new generations. In this case, as a result of an increase in the variability of individuals in the population and due to radiation selection, the radioadaptation of the population occurs, which reaches a higher level of radioresistance. The effects of exposure to an increased radioactive factor of the environment during this period are less noticeable.
Mortality and life expectancy. Radioactive radiation in large doses has a detrimental effect on animals in biogeocenoses. Thus, when irradiating a mixed forest with a dose rate of 0.5 Gy/day. there is a decrease in the number and death of individuals in the bird population. The death of birds is characterized by LD values of 5o / 30 in the range of 4.6-30 Gy.
Fertility. The fertility rate is a more radiosensitive parameter than the death rate. The minimum single doses of radiation leading to a decrease in the rate of reproduction may be less than 10% of the doses that are the direct cause of the death of animals.
Chronic ingestion of small doses of 90 Sr into the body of mice reduces the size of their brood. The radiosensitivity of the sex glands of different species varies greatly; however, female mice are among the most radiosensitive animals. Fertility in mice decreases after exposure of females to doses of about 0.2 Gy. Male mice are less sensitive, and doses above 3 Gy are required to reduce their fertility. Persistent infertility in female mice occurs after a dose of 1 Gy.
Reproduction intensity falls in contaminated areas due to the faster death of adults, the size of the brood decreases.
Development. There are developmental delays and various anomalies in the offspring of animals. Thus, when chicks are irradiated, they lag behind in the growth and development of plumage, especially if the irradiation occurred at the age of 2 days, and mice in territories contaminated with 90 Sr mature earlier and participate in reproduction.
Animal behavior. The change in the behavior of animals when they are irradiated with X-rays and -γ-rays consists in the recognition by organisms of the source of radiation and its avoidance. Features of the behavior of mice and rats, guinea pigs and monkeys in the field of γ-radiation indicate that higher vertebrates have the ability to determine the location of the radiation source and avoid