Summary on the radioecological state in the farming industry

About two decades have passed since Chornobyl NPP accident, the biggest catastrophe in the Human history. Consequently, more then 8 mln. ha of agricultural lands were contaminated.

¹³⁷Cs and ⁹⁰Sr are two main radionuclides determining the radiation state in contaminated territories of Ukraine now. Radionuclides are uptaken by human organism with foodstuffs mainly through the chain soil-plants-plant and animal production- organism of residents of contaminated territories. In such a way the human internal irradiation is formed. The total irradiation (total dose) consists of the internal and external irradiation.

Caesium-137 is the chemical analogue of potassium, which takes part in all metabolic processes in plants, animal and human organism, it has high biological mobility and removes from the organism rather fast. In 20-30 days after animals' passing on clean forage, still about one third of caesium-137, incame earlier, remain in the organism.

Strontium-90 is the chemical analogue of calcium, characterised by high uptake in plants and animals, it slow removes from the organism due to accumulation in a bone tissue. Contribution of strontium-90 in a human dose in a big part of contaminated regions can be disregarded in comparison to caesium-137, because ratio between activities of two radionuclides in soils of the biggest part of regions doesn't exceed 0.01, reaching sometimes 0.20. TF values for strontium-90 from all types of soil to plant production exceed caesium-137 ones, but Sr-90 transfer from a diet to animal production is lower then Cs-137 (5-10 times for milk and near 100 times for meat). Therefore, control for strontium-90 content is unnecessary, and agricultural countermeasures application should be planned, taking into account the density of soil contamination with caesium-137. All selected measures have to improve radiation state in a region both by caesium-137 and Sr-90.

During the time after ChNPP accident the radiation state in Ukraine became significantly better. The following actions and processes promoted it:

• performing of detailed radiation monitoring of farming industry, production, its control and rejection ;
• implementation of the complex of countermeasures in a field of farming industry directed to decrease the foodstuffs contamination ;
• natural rehabilitation processes, i.e. physical decay of radionuclides, their fixation in a soil and redistribution in the environmental objects.

Since the beginning of 1990s production with contamination, exceeding the state standards, hasn't already been produced in collective farms. That was permitted by detailed radiation monitoring and realisation of the countermeasures system in frame of the "Agricultural radiology" part included in "The state program of minimisation of ChNPP accident consequences " during the first post-accidental decade.

However, radionuclides content in the agricultural production manufactured in the private farms still now exceeds the state standards. Radioactivity of milk and meat in 40 settlements exceeds permissive levels (PL-97) 5-15 times constantly and in more then 400 settlements milk radioactivity in a big part ((>30%) of private farms can exceed PL-97. Simultaneously, cases of the radiocaesium content excess in potato, vegetables (near 10 settlements) and radiostrontium in grain crops (near 50 settlements) are happened , that wasn't found in previous years.

According to data of the radiological and dosimetric monitoring the structure of population exposure formation in various regions of Ukraine differs significantly at present time in comparison with the initial accidental period. The general tendency of the population dose formation in north-west Polessje regions is presented in Fig. The total dose of irradiation in this region varies in a range 0.5-5.0 mSv per year (by the requirements of "Standards for radiation safety of Ukraine" this dose hasn't exceed 1 mSv per year) and it forms mainly (80-95%) due to consumption of foodstuffs with the increased radionuclides content (predominantly ¹³⁷Cs). External irradiation accounts 5-20% of the total dose.

 Fig. Structure of the population irradiation dose formation in the north-west regions of Polessje at present time.

The total dose of population irradiation in central regions of Zhitomyr, Kyiv and Chernigiv districts reaches 0.2-1.0 mSv per year, the share of external irradiation of population accounts 50% of the total dose.

The dose of internal irradiation of population in the south regions of Kyiv district, in central and right-bank parts of Ukraine accounts only a few per cents of the total dose and doesn't exceed established standards.

Internal irradiation of population due to inhalation of radionuclides doesn't influence practically on formation of the total dose and accounts insignificant per cents.

About 360 thous. people live in the critical settlements where annual effective equivalent dose of population irradiation is near or exceeds 1 mSv. Annual collective dose of irradiation realised in these settlements is 200-400 person-Sv.