The Chernobyl accident: radiation impact on nature and animals

This article attempts to answer the most complex questions related to the problem of radioactive pollution of the environment as a result of the Chernobyl accident. The issues of ecology, the state of the plant and animal world of the planet, safety and protection from the consequences of environmental disasters are becoming more and more acute in our everyday life, as they touch upon the problems that most interest and worry people.

A few weeks after the Chernobyl accident, biologists and radiologists launched work to study the effects of radiation on wildlife in areas with high levels of pollution. First, the state of natural vegetation in the zone of severe pollution was studied at a distance of several kilometers from the accident site.

Pine forests, as expected, showed the greatest sensitivity to radioactive contamination. But by the end of June 1986, the dose rate in the crowns of trees had decreased by about 50 times due to radioactive decay and self-cleaning processes. The lethal effects in pine needles with an absorbed huge dose of radiation had been visually manifested by the end of the summer of 1986. The area of the dead forest adjacent to the Chernobyl industrial site from the west reached 400 hectares during the subsequent autumn-winter period.

Subsequently, this territory will be called the Red Forest. The greatest morphological changes were noted in areas with an average level of radioactive exposure: shortened, often curved and thickened shoot apical meristems, on which needles were partially preserved. Deciduous trees represented in the zone of severe pollution around the Chernobyl nuclear power plant, mainly birch, aspen, oak, practically did not suffer from pollution. Their radiation resistance is approximately 10 times higher than that of conifers.

Along with vegetation, the objects of study in the zone of severe radioactive contamination near the Chernobyl nuclear power plant were animals belonging to different taxonomic groups.

From July 1986 to April 1987, the abundance of the main groups of animals was calculated at different distances from the accident site in the soils of a pine forest of 50-60 years of age. Studies have shown that soil animals – inhabitants of the forest litter – were severely affected at a distance of up to 7 km from the nuclear power plant.

However, there was no catastrophic drop in the total number in the studied groups. It was comforting that the number and activity of soil invertebrates outside the limited zone of severe radiation pollution did not change significantly. It is believed that the maximum accumulated doses of radiation cause catastrophic changes in the microfauna community, while average doses cause registered but insignificant changes.

Therefore, a great relief for science was that no significant changes in the number and fecundity of wild animals had been noted outside the zone of strong radiation exposure. The observations did not establish any deviations in their seasonal rhythms.

The aquatic environment plays a special role in the redistribution of radionuclides, here the processes of their migration and accumulation are more intense than in terrestrial ecosystems. The main share of radionuclides that entered the surface water from the atmosphere in the first days after the accident quickly turned into bottom sediments.

Observations in the Chernobyl NPP cooler pond showed that the maximum concentration of radionuclides in phytoplankton occurred in the first two weeks after the accident, and in zooplankton 7-10 days after increased pollution of phytoplankton. The dynamics of radionuclide accumulation by fish is also characterized by a time delay in reaching maximum levels of radioactivity relative to phyto- and zooplankton.

The process of self-cleaning most quickly takes place in phytoplankton and much slower – in fish, they are more sensitive to radiation. When fish are exposed to chronic radiation, disturbances are observed in the functioning of individual organs, but overall, environmental sustainability is maintained at the population level.

Radioactive pollution of grazing and agricultural plants

The total intake of radionuclides from the soil into agricultural plants is the most important link in the food chain along which radionuclides from the soil are transported in the human body. The intensity of this transition is determined by many factors:

physico-chemical properties of radioactive particles that form soil pollution;

the “age” of radioactive contamination;

chemical properties of the compounds of the radionuclide itself;

agrochemical and mechanical properties of the topsoil;

type of plant;

climatic and landscape conditions.

With so many determining factors, the solution to the question of the action of each of them is possible only on the basis of long-term observations. It is important that the observations take place under the conditions of existing agricultural production with a sufficiently wide diversity of options of the soil & plant system in various soil, climatic, and geophysical conditions. This methodological approach was used to organize monitoring of radioactive contamination of grazing and agricultural plants on a network of landscape-geochemical and agroecological lands. The observing system was designed to cover the widest possible range of soil and climatic conditions.

The main objective of studies of radionuclide migration in the soil & plant system is to obtain generalized characteristics of the radioactive contamination of plants.

As noted, the migration properties of individual radionuclides depend on many natural factors and the physicochemical properties of the deposited radioactive substances. This remark fully applies to the transition of radionuclides to meadow plants, if we add the species of plants to the list of determining factors.

It is quite natural to expect (and this was proved by observations) that the migration properties of radionuclides will vary under conditions of such a multifactorial dependence widely depending on the options of the determining factors.

Since this dependence of the transition of radionuclides on the factors listed above is not well understood, when analyzing the data of field observations, the scientists grouped the results according to rather crude signs – time after the accident, type of soil, type of plants. These ranges were used in forecast estimates of the radioactive contamination of vegetation in the most typical environmental conditions.

Crop plants

The contamination of agricultural products was significantly affected by the fact that the release of radioactive substances occurred in late April – early May, when the main field work in crop production (sowing, planting) in the region (up to 150-200 km from the accident site) was completed, winter crops had already enough vegetative mass. In these conditions, the specialists of radio ecologists, when organizing constant monitoring of pollution of crop production in the contaminated territories, had the following tasks:

to evaluate the role of the initial stage of crop pollution in the first vegetation season of 1986 after the accident;

to determine the ratio of root and non-root inflow of radionuclides into agricultural plants in the first and subsequent years.

It was extremely important for scientists to find out the dependence of radioactive contamination of a particular type of agricultural plant on environmental factors. This concerned factors of physicochemical properties and density of radioactive fallout, soil, climatic characteristics, etc. This was necessary for prognostic evaluations of the profitability of crop production in contaminated areas in subsequent years and the adoption of necessary measures to reduce pollution. Obviously, the solution of these problems was important in connection with the need to predict radiation doses due to the consumption of locally produced food products. This irradiation channel was one of the main ones in the formation of total dose loads on the population. Therefore, the decrease in the accumulated dose was largely determined by the possibilities of limiting the dose of internal exposure due to food consumption. The main work was carried out by organizations of the agro-industrial complex.

Regular monitoring of the content of radionuclides in agricultural plants was carried out by scientists on a network of agroecological landfills located in the northern regions of Ukraine.

High-commodity grain farming was developed in these areas. The main crop is winter wheat, and sugar beets, potatoes and vegetables were also produced. A significant proportion of the cultivated land accounted for fodder crops – corn, seeded grass, fodder beets. Observations on the experimental field system began in August 1986.

The radionuclide content in the arable layer was determined once a season in each experimental field, in a typical plot of approximately 300 × 500 m. Samples of agricultural plants were taken during the period of maximum green mass and during harvesting, perennial grasses – before harvesting. To determine the degree of surface contamination, all plant samples were analyzed in two versions – in their natural (commercial) form and washed with a large amount of water.

In addition to determining the radionuclide content in soil and plant samples, precipitation, soil moisture and basic agro-meteorological characteristics, as well as yield, were monitored at all sites. Averaged observational results for the period 1987-1989 made it possible to identify a decrease in the transition of cesium-137 and strontium-90 among the main types of plant products.

This necessitated an individual approach to the forecast of radioactive contamination of a particular crop, both for specific soil and climatic conditions of the region and for pasture vegetation as a whole.

Thus, a very obvious picture is becoming apparent of what efforts were required from scientists to carry out tasks aimed at regulating processes that stimulate the restoration of flora and fauna contaminated with radionuclides and the rehabilitation of all living creatures that suffered as a result of the Chernobyl disaster.