O. Voitsekhovych, G.Laptev, V.Kanients UkrainianHydrometeorological Inst.Kiev

1. The Dnieper River Aquatic System Radioactive contamination: Long-term Natural Attenuation and Remediation O. Voitsekhovych, G.Laptev, V.Kanients UkrainianHydrometeorological Inst.Kiev o.voitsekhovych@gmail.com and Alexei Konoplev Centre for Environmental Chemistry “Typhoon”, Obninsk, Russia konoplev@obninsk.com

2. Why Aquatic Ecosystem proposed for consideration • Dnieper Basin and other rivers were significantly affected by Chernobyl radioactive fallout during initial period. • Secondary contamination of waters can last long, significantly extending the areas of initial contamination. This is caused by radionuclide dispersion via aquatic pathways (infiltration, wash-out, water transport, bio-accumulation & bio-transfer….) • Aquatic pathways do not normally cause significant human exposures (only in some specific cases) • However, public perception of risks, which may occur due to radioactive contamination of water bodies as a role, is inadequate and creates significant stress depended social tenses. Natural attenuation processes NA - in many cases are key factors in self-cleaning of the water bodies

3. Speciation of soils and radionuclide behavior • Mobility and bioavailability of radionuclides are determined by ratio of (1) radionuclide chemical forms in fallout and (2) site-specific environmental characteristics. This determines (a) the rates of leaching,(b) fixation/remobilization, (c) sorption-desorption of mobile fraction (its solid-liquid distribution). • The total distribution coefficient for radionuclides can vary in a wide range (4 orders of magnitude for radiostrontium and 5 orders of magnitude for radiocaesium) as a function of fallout characteristics and environmental conditions. • The total distribution coefficient for radionuclides is a dynamic characteristic and depends on transformation rates of chemical forms. • To reduce uncertainty in the estimates and predictions of radionuclide behavior, the exchangeable distribution coefficient Kdex was suggested to be used instead of Kdtot.

4. Selective sorption and fixation of radiocaesium • High retention of radiocaesium in soils is caused by two main processes: selective reversible sorption on illitic clay minerals and fixation. • Advanced methods have been proposed for determining the capacity of selective sorption sites (Frayed Edge Sites – FES) and exchangeable radiocaesium interception potential (RIPex). • Quantitative data were obtained for a wide range of soils and bottom sediments with respect to FES capacities andRIPex. FES RES

5. 137Cs monitoring studies in rivers, lakes, bottom sediment of reservoirs and Black Sea

6. Uncertainties in Assessment and Needs for Experimental Verification of the accidental consequences Radionuclide transport studies due to Runoff, sampling at the contaminated lands and water bodies

7. 90Sr Return water running off from floodplain and drainages In the Pripyat river, 10-20% of Cs and 40-70% of Sr originate the washed out from the ChNPP zone 90Cs Wash-off Snow melting effect

8. Pripyat River Floodplain around Chernobyl NPP was contaminated heaviest It is most significant source of 90Sr secondary contamination in Dnieper system. No significant impact by 137Cs, because high adsorption into the soil Contamination 1986 Flood protective dam has been constructed The most efficient water protection is to control water level and to mitigate inundation of the most contaminated floodplains by the flood protection sandy dykes constructed at left and right banks of the Pripyat river 1993 1999

9. 137Cs in the waters of the Dnieper reservoirs 137Cs activity concentration in water at the lowest reservoir returned to pre-accidental level in 1996-1998. In 2012, 137Cs activities in Kiev (upper reservoir) & Kakhovka (lower reservoir) in a cascade were at 10-15 Bq m3 & 0.5-1.0 Bq m3 range

10. 137Cs Bq/kg w.w. in freshwater fish (Kiev reservoirs and most contaminated lakes near ChNPP) 137Cs in predatory and non predatory fish species in Kiev reservoir (I.Ryabov et al., 2002) 137Cs and 90Sr in (a) predatory and (b) non-predatory fish at Gluboky Lake D.Gudkov, et al. 2008)

11. Collective Dose Commitment (CDC70) caused by 90Sr and 137Cs flowing from the Pripyat River (Berkovsky et al. 1996) Dose estimates for the Dnieper system: if there had been no action to reduce radionuclide fluxes to the river, the CDC70 for the Ukraine population (mainly due to Cs and Sr) could have reached3000 man Sv. Countermeasure works! Protective measures, which were carried out during 1992–1993 on the left-bank flood plain of the Pripyat River and later on right bank (1999) decreased exposure by approximately1000 man Sv. (Voitsekhovich et al. 1996).

12. Long-term dose assessment due to exposure via aquatic pathways Human exposure via the aquatic pathway took place as a result of consumption of drinking water,fish catch in reservoirs and agricultural products grown using irrigation water from Dnieper reservoirs. Estimated individual doses for people living along the Dnieper cascade through the aquatic pathways (far away from ChNPP) do not exceed 10 μSv y-1. However, estimated collective doses are rather high. No alternative water consumption. Stress component has to be primarily taken into consideration when the water protection actions is planned. Furthermore, in some closed lakes, the concentration of 137Cs remains high nin both water and fish. People who illegally catch and eat fish may receive internal doses of up to1 mSv per year from fish. The most significant contribution to the individual doses from aquatic pathways caused by 131I in the first week after the accident, but for very short time (Maximal values about 140 Bq/lobserved at the Kiev water intake plant 30 Apr 1986  Fukushima’s 150-250 Bq/l in a reservoir near Tokyo in March 2011)

13. Lessons learned • Although the Chernobyl radioactive fallout affected the large scale watershed areas and water bodies, the most of aquatic systems returned to their pre-accidental status within first decade after the accident. The main factors of self-rehabilitation of the water bodies were naturally attenuation processes. • Long-term radiological consequences for aquatic ecosystems will be mainly determined only at the most heavy contaminated lakes and wetlands at the Chernobyl NPP near zone. • Many inadequate water protection measures were carried out during initial post-accidental period because preparedness lacked, data and decision making support tools were in use, environmental radiation monitoring network has not been developed, impact of social stress was huge, and inadequate risk perception took place. • Scientifically defensive assessment tools and required data must be developed and applied as a basis for sufficient justification and water remedial actions optimization

14. Extra slide

15. Water protection and Remediation • Many remediation measures during initial period after the accident (1986-1988) were put in place, but because actions were not taken on the basis of dose reduction, most of these measures were ineffective. • Because of the importance of short lived radionuclides (e.g., 131I), early intervention measures, particularly changing supplies, can significantly reduce doses to the population. However this opportunity has been missed during first month since the accident. • During first months after the accident, restrictions on fishery and irrigation from the contaminated water bodies have been established. Many actions for the water regulation were applied at the small river in the Chernobyl exclusion zone. • Numerous new countermeasures that were applied months and years after the accident to protect water systems from transfers of radioactivity from contaminated soils were generally ineffective and expensive and led to relatively high exposures to workers implementing the countermeasures. • The only effective “late” countermeasure can be the water regulation at the most contaminated floodplains and water runoff regulation from the wetlands in the close zone around ChNPP.

16. Lessons learned cont’d • Countermeasure and remediation selection must be based on a cost-risk analyses that directly connects the main physical and chemical processes to environment (ecosystem) or human heath risks and costs • Decision makers must be knowledgeable on phenomena being evaluating, efficient in using expert’s experience and analytical and modeling systems. Right and reasonable decisions should mitigate or prevent expose of people, and should also allow “more” safe within the limited resources available. • Decision makers must communicate the facts quickly and honestly to the affected public. • Because the residual radioactive pollution still exists and our knowledge yet are not exhaustive, it is reasonableto continue research programs in ChNPP near zone as Unique Test site for radioecological studies.

17. The aquatic ecosystem radioactive contamination story, natural attenuation process and assessment for effectiveness of the water protection Y.Onishi, O.Voitsekhovych, M.Zheleznyak Chernobyl What Have we learned. The Successes and Failures to Mitigate Water Contamination over 20 years. Springer. 2007 http://www.springer.com/environment/book/978-1-4020-5348-1

18. Thank you very much for your attention

19. Duplicated slides

20. Fuel Particles in the Chernobyl fallout • Dominant part of radionuclides deposited on the soil surface in the Chernobyl NPP vicinity was incorporated within fuel particles. • Particles dissolution was the key process governing radionuclides mobility and bioavailability in soils during first years after the accident and several decades if particles were deposited to the water body sediments. After B. Salbu

21. Main messages from Chernobyl soil-water studies • Information on radionuclide deposition levels alone is not enough to accurately predict future and to assess human dose. • Data on speciation in fallout, rates of transformation processes and site-specific environmental characteristics determining these rates are needed. • Information on radionuclide chemical forms, their transformation in other words mobility and bioavailability should be taken into account when rehabilitation and decontamination strategies are developed on local or regional scale.

22. Experiments on runoff plots Snow melt wash-out studies • Available are results of the study radionuclides wash-off by rainfall and snowmelt surface runoff. These studies were conducted in the contaminated territories on the runoff plots of 1 m2 to 1000 m2. • Available are characteristics of runoff plots, speciation and content of 137Cs and 90Sr in soil, rain and runoff hydrographs, concentration of 137Cs and 90Sr in solution and on suspended matter in the run-off, and chemical composition of run-off and radionuclide speciation in soil for selected runoff plots. Artificial raining of the contaminated catchments

23. Radioactive contamination of the catchments and aquatic environment as versus of fallout formation date, its physical and chemical forms and also the landscapes at the deposited river watersheds Calculated plume formation according to meteorological conditions for instantaneous releases on the following dates and times (GMT): (1) 26 April, 00:00; (2) 27 April, 00:00; (3) 27 April, 12:00; (4) 29 April, 00:00; (5) 2 May, 00:00; and (6) 4 May, 12:00 (Borsilov and Klepikova 1993). 137Cs activity concentration in different rivers per unit of deposition, Smith, 2004

24. Radionuclides in Rivers Annual averaged 137Cs in the DnieperRiver Ratio of 90Sr and 137Cs in soluble forms in Pripyat River near Chernobyl 1012 Bq Radionuclide inlet to the Kiev reservoir. Pripyat River • The 137Cs concentration in river water has been shown to be directly proportional to the relative fraction of its exchangeable form in the surface soil layer. • The monitoring data allowed to validate mathematical models Spring flood Winter ice jam Rain flood Spring flood Spring flood

25. Sedimentation is a key factor of 137Cs removal from the water column to the bottom sediments Since 1991 to 2009 as result of several high floods the most of Cs-137 in bottom sediment has been removed with the sediment particles from the upper part deposited area to the down part sector of the Kiev reservoir Dnieper River Pripyat River Upper part of Kiev Reservoir 1998 Low part of Kiev Reservoir 137Cs 1991-93 1994 1994 Kiev Reservoir 2009 Data of UHMI

26. After Chernobyl 137Cs inventory in the 0-50 m layer increased by a factor of 6-10 and the total 137Cs inventory in the whole BS basin increased by a factor of at least 2 (pre-Chernobyl value of 1.40.3 PBq after bomb-testing fallout). 137Cs input from the Danube and the Dnieper rivers (0.05 PBq in the period 1986-2000) was insignificant in comparison with the short-term atmospheric fallout 137Cs-137 in the Black Sea

27. During initial period after the Chernobyl Accident the number of expensive actions to reduce secondary contamination of the rivers and groundwater have been applied. Most of the actions were extremely expensive and ineffective. Inadequate Radiation Risk Perception by Public was a key reason in WATER PROTECTION ACTION PLAN implementing Dose realization (%) during a 70 years for children born in 1986 For 1-st year about 47 % In spite of doses were estimated to be very low, there was an inadequate perception of the real risks by Public using water from contaminated aquatic systems. This factor made reasonable to justify some set of limited water remediation actions to reduce Public stressing and prevent further long term surface water contamination of the Pripyat For 10 years about 80% Years From I. Los, O. Voitsekhovych, 2001 Actual dose Public perception about Food product, milk water external inhalation