Consequences for agriculture6 April 2006
More than 4.5 billion hectares of agricultural land in Belarus, Russia and Ukraine were contaminated after the Chernobyl accident. In the two decades since, a wide range of large scale measures and remedial options have been implemented. By S.V. Fesenko, R.M. Alexakhin, M.I. Balonov, I.M. Bogdevich, B.J. Howard, V.A. Kashparov, N.I. Sanzharova, G. Voigt and Yu. Zhuchenka
The accident at Chernobyl gave rise to widespread contamination of agricultural lands throughout Europe by a range of radionuclides, including Cs-137. The countries most seriously affected include Belarus, Russia and Ukraine, where over 150,000km2 had contamination densities by Cs-137 exceeding 37kBq.m-2. In the most contaminated regions agriculture played – and plays – a major role in economic life, and rural inhabitants comprise a major part of the population affected by the accident. Under the same deposition scenario, the radiation impact on rural populations has generally been much higher than that of urban dwellers because in most cases they received higher doses due to environmental factors.
The ecological characteristics of most of the contaminated regions led to high radionuclide transfer to plants and subsequently animal products. Consumption of contaminated products in these regions was, and remains, one of the main radiation exposure pathways. Hence, the accident at Chernobyl has had a severe impact on the agriculture of Belarus, Russia, and Ukraine and the implementation of agricultural countermeasures was one of the main elements in the rehabilitation strategy. These countermeasures encompassed all aspects of agriculture, including farming, plant and animal production and food processing.
Five regions of Belarus, 21 regions of Russia and 12 regions of Ukraine have been officially recognised as regions which were adversely affected by the Chernobyl accident. The total area of contaminated agricultural lands (with a level of Cs-137 above of 37kBq.m-2) in these regions amounted to 4.66 million hectares, 990,000ha of which were contaminated at a level of above 185kBq.m-2.
Most of the soils in the most contaminated territory are of low fertility and present light sod-podzolic and peat soils. These soils have a low content of nutrients, humus, acidic pH, and are predominated by coarse sand and loamy sand. As a consequence, they are characterised by very high radionuclide mobility in soil and high root uptake, especially for peat soil. These low fertility soils are mostly distributed in the Gomel, Brest, Bryansk, Zhitomir and Rovno regions which were the most contaminated areas after the accident. The widespread distribution of these soils was one of the major factors contributing to the long-term impact of the accident on agriculture in the most contaminated regions.
More than 15,000 settlements with a population exceeding 6 million people resided in areas with a contamination density of Cs-137 above 37kBq.m-2 in 1986, and 640 settlements with around 272,000 inhabitants were located on land with a highly contaminated contamination density of soil exceeding 555kBq.m-2.
Radiation monitoring of contaminated soil
In the initial phase, I-131 was the radionuclide of most concern and milk was the main contributor to internal dose. Therefore the main aim of countermeasures application was to lower I-131 activity concentrations or to prevent consumption of contaminated milk by the population. Along with radioiodine contamination, both plants and animals were contaminated with radiocaesium isotopes and other radionuclides of secondary importance such as Zr-95, Ru-103, Ru-106, Ba-140, Ce-141 and Ce-144.
However, the information on countermeasures for milk was confined to managers and local authorities and was not distributed to the private farming system of the rural population. This resulted in limited application of the countermeasures with some delay, especially in rural settlements for privately produced milk, resulting in a high iodine uptake through the milk foodchain within a few weeks after the accident and, hence, to high doses to the thyroid for a relatively large number of people lived in affected areas. In many cases it was the main reason for thyroid cancer and other Chernobyl related diseases among the affected populations.
Within a few weeks after the accident, feeding of animals with ‘clean’ fodder began since this had the potential to reduce Cs-137 in cattle to acceptable levels within 1-2 months. However, this countermeasure was not in widespread use at this stage, partly due to a lack of uncontaminated feed at an early point in the growing season.
During the growing period of 1986, when there was still substantial surface contamination of plants, the major countermeasures in agriculture were of a restrictive nature. In the most heavily affected regions a ban was imposed on keeping dairy cattle. To reduce contamination levels in crops, an effective method was to delay harvesting of forage and food crops. Radiation monitoring of products was introduced at each stage of food production, storage and processing.
Based on a radiological survey performed from May to July 1986, approximately 130,000, 17,300 and 57,000ha of agricultural land were initially excluded from economic use in Belarus, Russia and Ukraine, respectively.
Directly after the accident an obligatory, selective and precautionary monitoring scheme was implemented together with a total survey of affected agricultural lands. The survey was implemented at the level of individual fields in the first few months after the accident, and continued for several years in the highly contaminated areas to evaluate changes with time in the radioecological status of the most affected areas.
During the first years after the accident, monitoring of foodstuffs, with the objective to provide a complete inspection of all agricultural products, was carried out on a large scale. Subsequently, areas that should remain under radiation monitoring have been identified, a system of observation was commissioned and quality assurance systems for both sampling and measurement campaigns were created.
Based on the results of the above monitoring programmes, 52 settlements in Belarus were relocated in 1989 because, after decontamination and application of countermeasures, it was considered that further implementation of countermeasures was not likely to lower doses to an acceptable level. Additionally in 1991, after two new laws were implemented, some people were allowed to resettle from contaminated areas and more settlements were relocated. In total, 470 Belarusian settlements were moved. For all these resettlements, animals accompanied their owners to the new locations when possible.
In the early 1990s, in Ukraine 101,285ha of agricultural lands (about 30% of which had a Cs-137 contamination level above 555kBq.m-2) were also withdrawn from agricultural use. Private cattle were moved with the people from these settlements. Provision of ‘clean’ foodstuffs produced in the collective sector or imported from ‘clean’ regions was organised for residents of the remaining settlements.
In Russia, in 1987-1988, evacuation of people and agricultural animals was carried out using a more elective method than in Ukraine. However, 17,300ha of agricultural lands were withdrawn from agricultural use and three collective farms and more than ten settlements were relocated. For the farms remaining, all sheep in the region contaminated over 555kBq.m-2 were removed because of the high transfer of radiocaesium to these ruminants. In the regions contaminated at a level above 555kBq.m-2, 6880 cattle were removed but many families retained their animals.
The effectiveness of different agricultural countermeasures in actual use on farms after the Chernobyl accident is presented in the Table on page 36. The reduction factors (ratio of activity concentration in the product before and after countermeasures application) achieved by each measure are given.
The priority in remediation of affected territories was focused on chemical amendments to improve soil fertility and reduce uptake of radiocaesium by crops and plants used for fodder. The extent to which each measure was used varied between the three countries. The recommendations on which countermeasures to use were repeatedly revised and updated.
Application of countermeasures on meadows was very effective in the three countries; in the most effective cases, the contamination of fodder decreased by a factor of 10-15. The nature of action and efficiency of radical improvement of hayland and pastures strongly depended on the types of meadow and on soil properties.
Cultivation of soil on the contaminated pasture
Countermeasures on arable soils included soil treatments such as ploughing, liming and application of potassium fertilisers. Application of one of the most effective options, deep ploughing (up to 50-70cm whereby the most contaminated upper soil layer is buried deep in the soil providing 5-10 fold reduction in accumulation of radionuclides by plants) was of very limited applicability in the affected area because of the dominance of only a shallow fertile layer. As an example of the extent of these countermeasures, liming was applied to 2.5 million hectares of agricultural lands, and more than 2.9 million hectares of soils received increased doses of potassium fertilisers in Russia for 15 years after the accident .
In the mid-1990s, the productivity of arable land fell because a worsening economic condition prevented the implementation of countermeasures at the previous rates, resulting in an increasing proportion of contaminated products. In some areas of Russia, this halted the previous decrease in the amounts of milk and meat exceeding radiation safety standards.
Even though problems of Sr-90 are less acute than those of Cs-137, some countermeasures have been developed and a 2-4-fold reduction in soil-plant transfer of radiostrontium following disking, ploughing and reseeding has been achieved.
Some plant species take up less radiocaesium than others as can be seen from experimental data collated in Belarus from 1997-2002. The extent of the difference is considerable and fodder crops, such as lupine, peas, buckwheat and clover, which accumulate high amounts of radiocaesium, were partly or completely excluded from cultivation.
The provision of uncontaminated (or less contaminated) feed to previously contaminated animals (clean feeding) for an appropriate period before slaughter effectively reduces radionuclide contamination in meat. This option has been one of the most important and frequently used countermeasures for meat from agricultural animals in all three countries. Official estimates of the number of cattle treated was between 5000 and 20,000 annually in the Russian Federation and 20,000 in Ukraine (supported by the government up to 1996). Clean feeding is combined with live monitoring of animals so that if radionuclide activity concentrations in an animal’s muscles are above action levels they can be returned to the farm for further clean feeding.
Live monitoring of animals before slaughter
Hexacyanoferrate compounds (referred to as ‘Prussian blue’) are highly effective radiocaesium binders, which may be added to the diet of dairy cows, sheep and goats as well as meat producing animals to prevent radiocaesium absorption in the gut and thereby reduce radiocaesium transfer to milk and meat.
Prussian blue has been intensively used in Russia and Belarus where between 15,000 and 30,000 dairy cows were treated annually from the early 1990s. In Ukraine, locally available clay mineral binders, which are less effective than Prussian blue but cheaper have been used.
A set of methods for milk processing to butter and sour milk products has been developed and successfully implemented in food processing practice. Depending on processing methods, the activity concentration in milk of Sr-90 and Cs-137 in a final (food) product can be reduced by up to 7-10 fold compared to the initial product (milk). A number of food products (such as starch, vegetable oil and spirit) can be produced in a virtually uncontaminated condition after processing of the contaminated raw material.
Radiological surveys of agricultural products showed that by the end of 1986 four regions of Russia (Bryansk, Tula, Kaluga and Oreol), five regions of Ukraine (Kiev, Zhitomir, Rovno, Volyn and Chernigov) and three regions of Belarus (Gomel, Mogilev and Brest) were still producing food products, which exceeded action levels for radiocaesium. In the most contaminated districts of the Gomel, Mogilev, Bryansk, Kiev and Zhitomir regions in the first year after the accident the proportion of grain and milk exceeding the action levels was around 80%.
From 1987, high radiocaesium activity concentrations in agricultural products were mainly observed in animal products, and application of countermeasures aimed at lowering Cs-137 activity concentrations in milk and meat was the key focus of remediation of affected regions. The contamination of potatoes, grain and root vegetables was of secondary importance, in spite of the fact that Belarus suffered the contamination of around 30,000t of potato and 25,000t of grain during first few years after the accident beyond action levels. The large-scale application of a range of countermeasures made it possible to achieve a sharp decrease in the amount of animal products with radiocaesium activity concentrations above action levels in all three countries (see Figure).
The changes with time in milk exceeding action levels can be seen in the Figure, but the values of action levels have been reduced with time in each of the three countries so the data is not directly comparable. Thus, differences in the time trend in the Figure between the countries largely relate both to the scale of countermeasures application and to changes in the action levels. This is particularly clear for Russian milk where the amount of animal products with activity concentrations above action levels rose after 1997 due to a considerable reduction in the action level combined with a reduction in countermeasure use. The recent reduction in meat above action levels in Ukraine and Belarus is because animals are now routinely live monitored before slaughter to ensure the meat is below the required level. In Russia, which also live monitors, the data is higher because they refer to both private and collective meat. The small tonnage of meat in each country above the action levels now is largely due to slaughter of animals that have been injured.
The maximum effect from remediation was achieved in 1986-1992. As a result of the implementation of remedial actions in affected areas (mainly radical improvement and clean feeding), contamination levels of animal products were gradually reduced and since 1991 the share of the production of animal industries has not exceeded 10% of the gross output obtained in any contaminated district. Thereafter, because of financial constraints in the mid 1990s, the use of agricultural countermeasures was drastically reduced and application rates of fertilisers were inadequate not only for a countermeasure but also for conventional food production. However, by optimising available resources, Cs-137 countermeasure effectiveness remained at a level which was sufficient to maintain an acceptable Cs-137 content in most animal products.
Reduction factors of different countermeasures
Large-scale remediation of the most contaminated regions has not only achieved a reduction in the amounts of foodstuffs keeping radiocaesium activity concentrations above action levels to a minimum, but also has provided a significant reduction in collective doses to the population consuming foodstuffs produced in affected areas. In other words there has been a reduction of the ‘exported’ dose.
The greatest contribution to the reduction in collective dose from consumption of contaminated foodstuffs (around 50%) has been achieved in the Gomel, Brest, Mogilev, Bryansk, Zhitomir and Rovno regions, where there has been the most heavy and widespread application of countermeasures. A significant (20-30%) reduction in collective dose as a result of application of countermeasures was observed in the Brest, Gomel, Kaluga, Chernigov and Kiev regions. A lower effect on reduction in collective dose has been achieved in regions where soils are more fertile in comparison to the low productivity Gomel, Bryansk or Rovno regions.
The contributions of individual countermeasure actions to the overall reduction of collective dose were dependent both on the structure of agriculture and the various characteristics of each remedial action implementation. As a rule, the key contribution to reduction of collective dose was determined by the effectiveness of countermeasures in animal breeding, because milk was the biggest contributor to the exposure of population after the Chernobyl accident. For example, in the contaminated districts of the Bryansk region this contribution was 65-75% of the total averted dose.
Intensive application of remedial actions in agriculture after the Chernobyl accident also needed to considerably reduce effective doses to the local population inhabiting affected rural areas. The actions described above were widely applied in areas with a high contamination density. On the basis of the studies carried out in rural settlements in 1991-1999, it was found that their application has lowered total annual effective doses to the rural population in areas with Cs-137 contamination density of 185-370kBq.m-2 by an average of 22%, in a zone with the contamination density from 370-555kBq.m-2 by 32% and in settlements with contamination density higher 555kBq.m-2 by more than 40%. The decrease in internal doses varied by a factor of between 3 and 8.
In the 20 years after the accident the total averted dose after implementation of countermeasures in rural settlements has been estimated to be approximately 4100man.Sv for Belarusian settlements, 3100man.Sv for Russian settlements and 4600man.Sv for Ukrainian settlements.
The contributions of the above remedial actions to the reduction of total dose received by the local population varied over different time periods after the accident. Thus, in the first several years, the relative contribution of restrictions on the use of privately produced milk and other foodstuffs was 90% of the total averted dose and after 1990 it dropped to 50-60%.
In spite of significant success in remediation of contaminated territories and widespread mitigation of the consequences of the accident it was not possible to provide safe living conditions for the whole population inhabiting affected areas. High contamination levels, high radionuclide transfer (especially from wet peat soils), and a sharp reduction in the scale of remediation has led to a rather high contribution by internal doses to the total dose. The main dose-forming product remains milk, however, in some forested areas contribution of forest products to the exposure of the population can reach more than 50%.
In Belarus there are 278 settlements with 60,800 inhabitants where annual effective doses are above 1mSv. During last five years production of milk with Cs-137 activity concentrations exceeding action levels dropped fourfold and the number of cattle with contamination of muscles above action level was less than 0.1% of the overall amount of cattle entering processing for meat production. However, the concentrations of Sr-90 above action levels are still found in samples of cereal grain and leguminous crops, as well as in samples of potatoes and milk produced in several districts of the Gomel region.
In Russia, in five of the most contaminated districts of the Bryansk region, there are around 180 rural settlements with a population of 33,500 inhabitants where the annual effective dose exceeds 1mSv. Contamination of milk in these settlements exceeds the current action level (100Bq/l) by up to a factor of 20. The inhabitants of these settlements have around 4000 dairy cows grazing on 12,000ha. In total, about 30% of milk and 50% of meat being produced in these settlements are above actions levels.
The activity concentration of Cs-137 and Sr-90 in foodstuff exceeds actions levels to some extent in five regions of Ukraine (Kiev, Zhitomir, Rovno, Volyn and Chernigov) and results, according to official information, in the annual effective dose exceeding 1mSv in 400 rural settlements. In the most radioecologically sensitive northwest territories of Ukrainian Polissya the effective doses to the population vary by 0.5-5.0mSv/year and are mainly formed (80-95%) due to the consumption of contaminated foodstuff. In some cases, national action levels for Cs-137 are exceeded in vegetables and potatoes growing on peat soil (in about ten rural settlements), and for Sr-90 in seeds (in about 50 rural settlements).
Thus, even 20 years after the accident, there are still large areas which still produce foodstuffs with radionuclide activity concentrations above actions levels. Furthermore, several hundred thousand people are still living in settlements with an annual effective dose above 1mSv where according to national legalisations remedial actions should be provided until 2045-2050 (according to model predictions), and further efforts are needed for optimising their application in the long term after the accident.
This work is largely based on the findings and recommendations of the Chernobyl Forum contained in its report entitled Environmental Consequences of the Chernobyl Accident and Their Remediation: Twenty Years of Experience, IAEA, 2006. S.V. Fesenko, M.I. Balonov and G. Voigt, International Atomic Energy Agency, 1400 Vienna, Austria; R.M. Alexakhin and N.I. Sanzharova, Russian Institute of Agricultural Radiology and Radioecology, 249020 Obninsk, Russia; I.M. Bogdevich and Yu. Zhuchenka, Research Institute for Soil Science and Agrochemistry, Minsk, Belarus; B.J. Howard, Centre for Ecology & Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LAI 4AP, UK; V.A. Kashparov, Ukrainian Institute of Agricultural Radiology (UIAR), Mashinostroiteley Str.7, Chabany, Kiev Region 08162, UkraineRelated ArticlesConsequences for healthFilesFigure: Amounts of milk and meat exceeding action levels in Russia (all milk and meat - collective and private), Ukraine and Belarus (only milk and meat entering processing plants) after the Chernobyl accident, tonnesExternal weblinksNuclear Engineering International is not responsible for the content of external internet sites.Link to the Chernobyl Forum site on the IAEA website Focus on Chernobyl