Active human activity very often adversely affects the surrounding world of animate and inanimate nature. The rapid development of industry, the intensive development of agriculture, the difficulties of waste disposal - all this seriously threatens the ecology of the planet. With the development of nuclear energy and the improvement of nuclear weapons, another problem arose - radioactive pollution of soils, water bodies, and the atmosphere.
Problem definition
Radioactive contamination of the soil is the excess of radionuclide concentration in it over the maximum permissible norm due to anthropogenic activity.
Contaminated areas are characterized by significant excess doses of external and internal exposure. To indicate the rate of ionizing cure, the International Commission on Radiation Protection (ICRP) introduced an average annual dose of radiation, which for soils and rocks is 0.25-0.5 microsievert per year (mSv / g). This norm defines the amount of radiation safe for human health and is many times lower than the value that can lead to the death of a living organism over the next 30 days.
Causes
How does radioactive soil contamination occur? Sources of pollution are two groups of radionuclides:
It is known that the soil contains natural radionuclides. But their concentration is significantly increased due to the extraction, storage of natural raw materials, processing, fertilizing, their production, burning coal, using ash as fertilizer for plants or for the manufacture of building materials, etc.
Due to the rapid production and use of fertilizers, the number of contaminated soils is increasing every year. For example, the question of increasing the concentration of radionuclides in the soil due to the use of potash and phosphorus fertilizers has not been sufficiently studied.
Artificial radionuclides massively fall into the components of the planet’s biosphere due to nuclear explosions.
Thus, the main causes of radioactive contamination of the soil cover are:
- intensive development of agricultural land;
- heavy industry;
- development of mineral deposits;
- radioactive waste burial;
- nuclear radiation emissions;
- nuclear weapon test.
Radioactive Soil Contamination: Consequences of Contamination
There are many negative effects of soil pollution:
- direct negative impact of radioactive substances on animals, vegetation and humans;
- a significant limitation on the ability to use soil resources for agricultural purposes. Indeed, all products that are received from such a land plot have excess levels of the concentration of radioactive substances due to pollution of open water bodies and groundwater, where harmful compounds are washed out of the soil. Heavy pollution can make it impossible to use fresh water not only for drinking and cooking, but also for drinking livestock or irrigating agricultural land.
Many scientists argue that damage by environmental radiation substances leads to the complete death of biogeocoenoses and populations. This occurs at high pollution levels. Such sites are recorded mainly near the places where radiation was released and, as a result, radioactive contamination of the soil. Chernobyl is an exclusion zone after the Chernobyl accident. Then hundreds of hectares received the strongest dose of radiation, as a result of which they were completely withdrawn from human life.
Deep processes
Soil absorbing complex sorts radioactive substances. In addition, he stores them for a long time.
Radionuclides in the soil are characterized by:
- properties of chemically active isotopes;
- properties and composition of the soil itself;
- properties of radionuclides in fallouts;
- climatic indicators;
- landscape features.
Radionuclides enter the soil surface as part of aerosols, minerals, fuel particles, etc. The maximum portion of their soluble fractions in the global precipitation is 30-90%. This indicator is highest for cesium and strontium. No one knows how radionuclides will behave in the future. Dynamic equilibrium increases as the solubility of their precipitation decreases. The introduction of soluble organic substances into the soil and a special acidification of the medium affects the increase in the migration of radionuclides, which is used to purify it.
The mobility of radiation pollution depends on:
- mineralogical composition;
- the presence of geochemical barriers in the soil;
- particle size distribution;
- humus properties;
- reaction medium.
Horizontal redistribution of radionuclides
To predict the possible consequences of radioactive contamination of the soil, it is very important to know the features of radionuclide migration.
Redistribution of radionuclides in the soil occurs in the horizontal and vertical directions in a natural way and for reasons of anthropogenic activity.
Horizontal migration occurs due to:
- eolian transfer (the name comes from the name of the god of the winds Aeolus);
- flood of flood waters, which is the cause of more intense pollution of lowlands and wetlands;
- livelihoods of animals (earthworms, wild boars, moles and other "digging");
- traffic movement;
- harvesting green fodder in polluted meadows;
- forest fires, which are a very powerful factor in isotope transport.
The minimum horizontal migration is observed in forest cenoses, and the maximum - in agrocenoses with light soils. Horizontal redistribution, on the one hand, reduces the level of contamination of soils with radioactive nuclides, and on the other hand, expands the area of their distribution.
Vertical migration
As for the vertical redistribution, it occurs slowly in all types of soils . The linear speed of this process is from tenths to two centimeters per year. The soil in this case plays the role of a biogeochemical barrier. Studies conducted in the Chernobyl zone showed that the bulk of the radionuclides for a long time remains within the upper soil layer (about 10 cm). And in the forest part of this zone, radioactive substances accumulated in the litter (foliage, needles) and the lower soil layer (about 1-2 cm).
Vertical migration of radionuclides depends on such factors:
- volcanic eruption;
- rains, moisture transfer by runoff and vapor;
- transfer by plant root systems;
- human activities - plowing, irrigation.
The most polluted territories on the planet
There are hundreds of radioactively contaminated territories on the planet. A serious danger is the territory of Hanford in the state of Washington, USA. Here, in the middle of the last century, a gigantic complex was built that was engaged in the world's first nuclear development. As a result of its activities, an area of 518 square meters has been polluted. km
Soils in Somalia were used for illegal disposal of nuclear waste. The Semipalatinsk test site in Kazakhstan, where nuclear tests were conducted, is one of the most radiation hazardous areas in the world. In the city of Mailuu-Suu, Kyrgyzstan, uranium mining was launched on an all-Union scale, which led to an extremely high concentration of radioactive isotopes in the mine district.
The well-known Chernobyl zone is a dead zone where radioactive contamination of soils occurred over many hundreds of kilometers. The Chernobyl nuclear power plant is not the only nuclear power plant in the world where a world-wide nuclear disaster occurred. A similar thing happened in Fukushima, Japan. Here, an earthquake and tsunami in March 2011 caused an accident at a nuclear power plant, which affected a huge territory.
The Mayak industrial complex in Russia in the secret city of Chelyabinsk-40 near the city of Kyshtym suffered from an accident in 1957. Its consequences were radiation pollution of 25 thousand hectares of arable land. A similar catastrophic situation has developed around the Siberian Chemical Plant OJSC in the Tomsk Region, Russia.
Features of the use of contaminated areas
Radionuclides with a long decay period mainly accumulate in the soil: promethium-147, cerium-144, cesium-137, ruthenium-106 and 103, strontium-90. The most dangerous for living organisms is strontium-90. Therefore, in fields contaminated with radiation, agrochemical, agrotechnical and other measures are carried out that can reduce the transfer of hazardous compounds from soil to plants. For this purpose, the topsoil is also cut off with subsequent burial.
An effective measure is the sowing of plants of certain varieties and species, which are characterized by a minimum level of accumulation of radionuclides. Everyone knows that in animal husbandry, only clean feed should be used for fattening. Special additives of sorbents are also used, which suppress the transition of radioactive substances into milk.
Reclamation work is aimed at reducing the flow of radionuclides into plants. For this, sorbents are introduced into the soil, such as: vermiculite, zeolite, mineral and organic additives, lime. In agriculture, a decrease in the accumulation of radionuclides in a plant occurs with the help of agricultural techniques. Conduct planting plowing, with a turnover of the reservoir. This technique of soil cultivation leads to a deepening of radioactive contamination. Due to this, the accumulation of substances in plants is reduced by 24 times. In agriculture, the structure of crop rotation should be changed. It is better to start growing industrial crops that are not used in food.
An alternative method of using the contaminated area is to eliminate any specific impact. For example, you can create special reserves. With a pronounced radiation background , a forest, mainly pine, is planted at the site of infection.
Security measures
Security measures in territories where there is radiation pollution of the soil are aimed at reducing the negative impact of radiation. The following actions are carried out:
- development of a strategy for the use of products and territory at the national or international level, depending on the extent of pollution and the potential risk of contamination of the surrounding areas;
- land reclamation, agrotechnical measures;
- chemical disinfection;
- use of sorbents;
- restriction of human activity;
- informing the public about the possible danger;
- restriction of the export of any product from a dangerous territory.
The duration of these restrictions depends primarily on the density of contamination. In addition, pay attention to the exposure dose of radiation. This period can last from several weeks to many decades. Thus, ecologists reduce the radioactive contamination of soils and its consequences.