Radionuclide pollution

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4.4.3.  Radionuclide pollution

 

Radionuclide pollution refers to the adverse effects of the release of radioactive contaminants and wastes into the aquatic environment from human activities. The transboundary significance of this issue is illustrated by the fact that the Chernobyl accident affected the territories of many countries, including the three nations of the Dnipro Basin (Table 4.1). A detailed causal chain showing the links between the immediate and underlying causes of this issue is shown in Figure 4.13.

 

 

The major sources of radionuclide pollution in the Dnipro Basin are the territories contaminated as a result of the Chernobyl accident, nuclear power plants (NPP’s), radioactive material extracting/processing industries and radioactive waste disposal sites.

Environmental impacts

Impacts on human health and ecosystems from uranium mines and related processing industries

Uranium mines and related processing industries in Ukraine have a number of potential impacts on human health and the environment. They include:

 

- Contamination of mining process water with uranium and other radionuclides;

- Discharge of processing industry effluents to surface waters (usually after treatment);

- Surface runoff from contaminated mining and processing industry sites;

- Radon release from mines and mining/processing waste disposal sites;

- Leaching of radionuclides from tailings and their subsequent transport by river flow;

- Erosion of tailing waste sites leading to the spread of the fine tailing fraction by high winds and migration through water;

- Contamination of surface waters and groundwater sources by poisonous non-radioactive substances (e.g. heavy metals and chemical reagents used in

  the ore-enrichment process).

 

Radioactive effluents received by the Zheltaya and Saksagan Rivers, and the Dnipro reservoirs from uranium mines and ore-processing industries are usually associated with relatively low chronic exposure levels, although radioactive pollution levels can be as high as 1 Bq/l at or immediately downstream of mining process water outlets. Consequently, this may result in additional exposure of the local population through consumption of river water.

 

Impacts on human health and ecosystems as a result of the Chernobyl accident

 

The most serious consequences of the Chernobyl accident for the population were caused by exposure to short-lived radionuclides, especially ¹³¹I, which resulted in many thyroid cancers. Other health effects are expected to become apparent in the future. The contribution of freshwater pathways to human exposure is dependent on the direct consumption of water, fish and irrigated farming products, as well as meat and milk produced in the contaminated areas where the river floodplains are used for livestock grazing and haymaking.

 

The concentrations of ¹³⁷Cs and ⁹⁰Sr in the Dnipro Basin watercourses are now well below the national limits and international guideline levels for drinking water. However, enclosed lakes with no regular outflow still present a radiological problem that will continue for some time. These lakes, usually associated with underlying peat deposits, have a limited ability to fix ¹³⁷Cs. As a result, concentrations of ¹³⁷Cs in these waters are close to the maximum admissible limits. The levels in local fish species also exceed these limits by at least an order of magnitude. Moreover, radionuclide levels exceed maximum admissible limits in local forest products (wild game, mushrooms, and berries), and in milk and meat produced by cattle grazing on the contaminated floodplains. The contribution of freshwater pathways to human exposure of ⁹⁰Sr and ¹³⁷Cs in water, ranges from 0.2% to 1.0% within the Russian Federation, from 0.1% to 1.5% within Belarus, and from 1% to 7% within Ukraine (i.e. up to 1 mSv per year in absolute terms).

 

Strontium transport from the Chernobyl Exclusion Zone to the Dnipro reservoirs increases significantly during high flow periods. Although individual exposure levels remain low (below 1 mSv), collective exposures may reach 20-30 Sv per cap/year, or even 60 Sv per cap/year as a result of radionuclide transport from the Zone.

 

Enclosed lakes located in the Republic of Belarus and the Bryansk Oblast of Russia are considered as local hot spots in terms of average annual human exposure doses. Even 16 years after the Chernobyl fallout, the exposure dose of the local population living near the Kazhanovsky Lake (in the Bryansk Oblast) can reach 6-10 mSv due to consumption of local fish. In 1987-1988, annual collective radiation dose values ranged from 5.1 to 7.6 Sv per cap/year. By 1998 the value had reduced to 3 Sv per cap/year, a twofold reduction. Similar individual exposures were recorded in the areas adjacent to the most heavily contaminated lakes in Belarus.

 

The direct effect of radioactive pollution on species diversity has only produced a response in pedogenetic invertebrate communities. Other wildlife communities have been more severely affected by secondary ecological factors of radioactive pollution. For example, direct exposure levels in the areas affected by the Chernobyl accident appear to be below lethal levels that would be expected to cause mass kills among wildlife communities, although the resultant radionuclide levels in many species have made them unsuitable for human use. This has had an indirect effect on the abundance and diversity of many wildlife species, especially commercial ones.

 

Two opposite processes have developed in the most contaminated areas withdrawn from use immediately after the Chernobyl accident. There has been a dramatic drop in the population of synanthrope species, followed by their virtual disappearance and an increase in the population of a number of species vulnerable to anthropogenic effects. Likewise, trends in bird’s communities have followed a similar pattern with a reduction of species diversity and populations of synanthrope communities as opposed to the progressive development of communities that are characteristic to woodland/shrub ecotones and successions. In particular, there has been an increase in the population of those carnivorous species that are vulnerable to anthropogenic effects. Similar trends have been reported for other wildlife communities.

 

Key features of radionuclide accumulation patterns are as follows:

 

- In aquatic phytocenoses, the ability to take-up and accumulate ⁹⁰Sr and ¹³⁷Cs is most pronounced in macrophyte species (Typha latifolia and Elodea canadensis), and in algal communities dominated by Cladophora and Oedogonium families.

- Radionuclide levels in various parts of aquatic plants were found to be subject to seasonal variations, with radionuclide accumulation rates being proportional to the concentrations of their macroanalogues in non-aquatic plants.

^{- 137}Cs levels were measured in fish inhabiting the Kazhanovsky Lake in the Bryansk Oblast of Russia, and other lakes of a similar type in the Gomel and Mogilev Oblasts of Belarus. There appeared to be differences amongst species within lakes, with ¹³⁷Cs levels generally highest in predator fish. Based on these results, a suite of indigenous fish species may be ranked in terms of increasing levels of ¹³⁷Cs: gudgeon, crucian, tench, pike, and perch. Accumulation levels in fish samples varied within the range of 320 to 6,000 Bq/kg (wet weight). There also appeared to be a direct relationship between accumulation rates and fish age. In 1993, average ¹³⁷Cs levels in perch of 10-years of age were 40 kBq/kg (wet weight), exceeding EU guideline levels of 0.6 kBq/kg of wet weight by about twofold.

 

Results of a series of surveys carried out in the Republic of Belarus between 1986 and 1998 indicate that macrophytes, zoobenthos and fish inhabiting local water bodies contained higher levels of radionuclide pollution.

 

In 1986-1987, immediately after the Chernobyl accident, extremely high radionuclide pollution levels were recorded in the common reed (up to 1.63´10³ Bq/kg of Cs₁₃₄; 7.03´10³ Bq/kg of Cs₁₃₇; 4.07´10⁴ Bq/kg of Cs₁₄₄; and 4.81´10⁴ Bq/kg of Nb₉₅). The Spongia species were found to contain up to 5.9´10³ Bq/kg of Cs₁₃₄, and 1´10⁴ Bq/kg of Cs₁₃₇, with a total beta-activity level of about 128,000 Bq/kg.

 

In fish, the highest levels of Cs₁₃₇ were recorded in catfish (6´10⁵ Bq/kg) and pike perch (4.4´10⁵ Bq/kg). Results of surveys carried out in the Kyiv reservoir between 1987 and 1991 suggest that shellfish communities were more responsive to Sr₉₀, with Cs_{134, 137} levels being generally higher in fish. The highest levels of Cs_{134, 137} (up to 6.29´10³ Bq/kg) were recorded in pike in the autumn of 1987 and the winter of 1998. Bottom sediments are estimated to contain over 90% of the total stock of

Cs₁₃₇ in the aquatic ecosystem.

 

Further information on radionuclide contamination can be found in Section 3.3.2 (Review of the 2000-2001 field survey results).

Immediate causes

The following immediate causes contribute to radionuclide pollution in the Dnipro (also refer to Table 4.17):

- Atmospheric and aquatic releases of radionuclides during the Chernobyl accident;

- Secondary releases as a result of the Chernobyl accident;

- Point and diffuse discharges of mining process waters and tailing wastes from disposal sites at uranium mines and ore-enrichment plants;

- Emissions/discharges from radioactive waste disposal sites and ionising radiation sources;

- Emissions and discharges from NPP’s.

 

1. Atmospheric and aquatic releases of radionuclides during the Chernobyl accident and subsequent secondary releases

 

The Chernobyl accident resulted in the contamination of extensive areas of woodland and farmland and continues to be a serious problem in the Basin.

 

Radioactive contamination is considered to be the major environmental problem in the Belorussian part of the Dnipro Basin, with extensive areas of agricultural land contaminated by ¹³⁷Cs. Approximately 1.1 million hectares (89.7%) of Belorussian agricultural land contaminated by ¹³⁷Cs (>1 Cu/km²) is located in the Dnipro Basin (See Section 3.1.2 and Figure 3.3 for more details). The Gomel and Mogilev Oblasts(674,200 and 332,500 hectares respectively) have suffered most from radioactive contamination of agricultural land.

 

In addition, surface runoff and ground water flow from contaminated areas has significantly contributed to the existing levels of radionuclide pollution in the Dnipro Basin (including washout of contaminated soil particles and radionuclide metabolites during high flow periods). Surface runoff from contaminated areas results in elevated concentrations of radionuclides in water, bottom sediments and biota. Table 4.10 shows the levels of radionuclides found in water samples taken from the Pripyat River within Ukraine immediately after the Chernobyl accident in May 1986.

 

During the 2000-2001 field survey organised within the framework of the current UNDP-GEF Dnipro Programme and supported by the International Development Research Centre, a special analytical programme was carried out to investigate the levels of radiological contamination and distribution patterns throughout the Dnipro Basin.

 

The results of this survey show that the area most contaminated by radionuclides lies in the Pripyat Basin immediately upstream of the Chernobyl NPP, where ⁹⁰Sr levels were estimated at 8,000 Cu. Levels of ¹³⁷Cs, ²³⁹Pu and ²⁴⁰Pu in soil were also extremely high in this area. However, these radionuclides are bound with soil particles and therefore their contribution to human exposure via freshwater pathways is relatively minor, especially in the post-Chernobyl period.

 

Table 4.10. Levels of Radionuclides found in water samples from the Pripyat River, 1986

 

The migration characteristics of radionuclides can be understood from an appreciation of the chemistry of Cs and Sr. Cs has the ability to be taken up by clay materials frequently occurring in natural soils, thereby weakening its horizontal and vertical migration. Sr is less firmly bound by soil, being more mobile in the environment. The soils in the Chernobyl Exclusion Zone are heavily contaminated with ⁹⁰Sr, and this contaminant can be washed out during flooding events. The chemistry of these elements also explains their behaviour upon entering the Dnipro reservoir chain, where ¹³⁷Cs is fixed onto clay sediments in the deeper sections of the reservoirs, especially in the Kyiv reservoir. Very little ¹³⁷Cs passes through the whole chain of reservoirs, therefore the levels of ¹³⁷Cs in river flow entering the Black Sea are very similar to background levels. On the other hand, although ⁹⁰Sr levels progressively decrease downstream (mainly due to dilution), a significant proportion of the pollution load reaches the Black Sea.

 

Table 4.11 reflects annual radionuclide fluxes into the Pripyat River expressed in absolute terms for a dry year (1997), a wet year (1999) and an average year (2001). The contribution of the Pripyat River tributaries (Uzh, Braginka, and Sakhan) to the total radionuclide load transported by freshwater pathways has not exceeded 13% in recent years.

 

Analysis of ⁹⁰Sr migration data provided by the Chernobyl Exclusion Zone Administration suggests that the highest contribution of radionuclide pollution to the Dnipro water system is associated with the area adjacent to the Chernobyl NPP site, varying from year to year between 60% and 70%. The total radionuclide pollution load has been continuously decreasing, with 1999 being the only exception due to exceptionally high flooding in the Pripyat River Basin.

 

Table 4.11 Source-specific fluxes of ⁹⁰Sr into the Pripyat River

 

 

⁹⁰Sr remains a priority radionuclide contaminant transported by river flow beyond the boundaries of the Chernobyl NPP site (Table 4.12.). In addition, ¹³⁷Cs, ²³⁹Pu and ²⁴⁰Pu enter the rivers in the Basin with soil particles as a result of erosion developing in the river catchments and floodplains. These radionuclides are carried downstream with sediments and deposited in the upper section of the Kyiv reservoir. However, they are characterised by relatively low bioavailability levels. Accordingly, radioactive pollution levels in river fish and biota have now significantly reduced, and the embargo on fishing activities in the reservoirs has been lifted.

 

Table 4.12 Estimated stocks of cesium-138 and strontium-90 in catchments of major rivers entering the Kaniv reservoir

 

Further information on the redistribution and accumulation of radionuclides originating from the territories affected by the Chernobyl accident can be found in Section 3.3.2 (Review of the 2000-2001 field survey results).

 

2. Point and diffuse discharges of mining process waters and tailing wastes from disposal sites at uranium mines and ore-enrichment plants.

 

Uranium mines are concentrated in the Ukrainian part of the Dnipro Basin. The amount of radioactive waste material generated by uranium mines and ore-enrichment plants in Zheltye Vody and Dniprodzerzhinsk is now higher than 65 million tonnes. A significant amount of natural radioactive material is extracted and processed by mining and ore-enrichment industries, contributing to the total radioactive pollution load on the local environment. Uranium ore fields and tailing waste disposal sites are major sources of potential radioactive contamination. Surface runoff and leachate migration from tailing waste disposal sites results in elevated levels of radionuclides in local rivers, although they remain below the maximum admissible levels set for drinking water sources. Further information on radioactive pollution sources within the Dnipro Basin can be found in Section 3.3.4.

 

3. Emissions and discharges from nuclear power plants

 

There are 20 nuclear power reactors in the Dnipro Basin, 13 of them operating at four nuclear power plants within Ukraine (the Zaporizhzhia, the South-Ukrainian, the Rivne, and the Khmelnitsk NPP’s), and 7 in the Russian Federation at two sites (the Kursk and Smolensk NPP’s).

 

Results of the IAEA expert review of emission/discharge statistics and monitoring data on performance of nuclear power facilities in Ukraine and Russia suggest that routine discharges from NPP’s are generally well below mandatory limits, and their environmental impact is rather limited. Operators of nuclear power generating facilities and radioactive waste disposal sites maintain strict control of pollution migration beyond their sanitary zones. Total annual radioactivity levels associated with process water discharges into water bodies don't exceed 1-2 Cu/year. Waste products are generally well managed at these facilities, with continuous improvements in waste management and waste minimisation being implemented. Waste and spent fuel facilities feature adequate environmental protection systems, although they are reaching capacity in some instances.

 

Underlying sectoral causes

 

The underlying sectoral causes of radionuclide pollution are mainly associated with resource uses and practices in the mining and energy sectors. A significant proportion of radionuclide pollution load on the Dnipro Basin is a direct consequence of the Chernobyl accident. A list of the priority sectors for all issues is presented in Table 4.18 (Section 4.7)

 

A detailed causal chain reflecting the links between the immediate and underlying sectoral causes of this issue is shown in Figure 4.13 and a detailed description of terminology used in this causal chain is given in the definition of terms in Annex 2.

Priority inter-sectoral issues

Based on the causal chain in Figure 4.13, the priority sectoral resource uses and practices and the underlying political, economic and governance causes of this transboundary issue can be identified. These are shown in the Strategic Action Programme (SAP) decision making management tool (Figure 4.14).

 

 

The SAP decision making management tool shows the priority sectors for this issue (colour coded with the causal chain) together with three hierarchical levels of concern (shown in Section 4.3.1). Within each level the priority resource uses and practices and the underlying political, economic and governance causes for each transboundary issue are listed. These can either cut across all sectors (e.g. Lack of adequate finance) or be sector specific (e.g. location and concentration NPP’s in the Basin).

Justification for sectoral prioritisation

The causal chain for the issue of Radionuclide Pollution is quite specific: for example, the consequences of the Chernobyl accident have been identified as an individual sector, which is relevant for the analysis of this issue.

 

Analysis of the radionuclide pollution issue, carried out by the IAEA experts, suggests that the mining industry (including mining and enrichment of uranium ore) has had a profound impact on the environment. This is illustrated by the fact that the amount of tailing waste accumulated in the Basin as a result of past activities is about 100 million tonnes. The majority of tailing waste storage sites have not been closed/restored properly, and this is likely to pose a long-term problem unless these sites are adequately managed. The tailing waste storage site “D” in Dniprodzerzhinsk is considered to represent the major danger in terms of potential environmental pollution due to its proximity to the Dnipro River, poor technical state and the perceived risk of catastrophic failure of its bund.

 

Limited data is available on radionuclide concentrations in the vicinity of uranium mines, processing sites and radioactive waste disposal sites. It is therefore impossible to provide any accurate assessment of exposure doses associated with these sources. Therefore this sector is considered of top priority.

 

The second priority sector is nuclear energy. This is explained by the fact that emissions during routine operation of nuclear power facilities in Ukraine and Russia are relatively minor and far below existing mandatory limits. The RBMK and VVER reactors have been subject to major regional and international scrutiny. Immediately after the Chernobyl accident, urgent measures were taken to improve the inherent safety of these reactors. An international in-depth safety assessment process is currently underway to optimise these programmes. There is space for improvement of the system of emergency preparedness and response.

 

The third priority sector is defined as “Consequences of the Chernobyl accident”. According to the IAEA data, transboundary transport of radionuclides in the Dnipro Basin is currently very close to the background levels, i.e. has practically restored to the pre-Chernobyl levels.