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

Why Aquatic Ecosystem proposed for consideration NA - in many cases are key factors in self-cleaning of the water bodies Natural attenuation processes 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.

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 FESRES 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 (RIP ex ). Quantitative data were obtained for a wide range of soils and bottom sediments with respect to FES capacities and RIP ex.

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

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

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

It is most significant source of 90 Sr secondary contamination in Dnieper system. No significant impact by 137 Cs, because high adsorption into the soil Flood protective dam has been constructed 1999 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 Pripyat River Floodplain around Chernobyl NPP was contaminated heaviest Contamination

137 Cs activity concentration in water at the lowest reservoir returned to pre-accidental level in In 2012, 137 Cs activities in Kiev (upper reservoir) & Kakhovka (lower reservoir) in a cascade were at Bq m 3 & Bq m 3 range 137 Cs in the waters of the Dnieper reservoirs

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

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 reached 3000 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 approximately 1000 man Sv. (Voitsekhovich et al. 1996). Collective Dose Commitment (CDC70) caused by 90 Sr and 137 Cs flowing from the Pripyat River (Berkovsky et al. 1996)

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 137 Cs 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 131 I in the first week after the accident, but for very short time (Maximal values about 140 Bq/l observed at the Kiev water intake plant 30 Apr 1986  Fukushima’s Bq/l in a reservoir near Tokyo in March 2011)

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

Extra slide

Water protection and Remediation Many remediation measures during initial period after the accident ( ) 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., 131 I), 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.

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 reasonable to continue research programs in ChNPP near zone as Unique Test site for radioecological studies.

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

Thank you very much for your attention

Duplicated slides

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. 20 After B. Salbu

Main messages from Chernobyl soil-water studies 21 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.

Experiments on runoff plots 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 m 2 to 1000 m 2. Available are characteristics of runoff plots, speciation and content of 137 Cs and 90 Sr in soil, rain and runoff hydrographs, concentration of 137 Cs and 90 Sr 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. Snow melt wash-out studies Artificial raining of the contaminated catchments

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). 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 137 Cs activity concentration in different rivers per unit of deposition, Smith, 2004

Radionuclides in Rivers Annual averaged 137 Cs in the Dnieper River Ratio of 90 Sr and 137 Cs in soluble forms in Pripyat River near Chernobyl Bq Radionuclide inlet to the Kiev reservoir. Pripyat River The 137 Cs 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 Rain flood Spring flood Winter ice jam

Sedimentation is a key factor of 137 Cs removal from the water column to the bottom sediments Sedimentation is a key factor of 137 Cs removal from the water column to the bottom sediments Upper part of Kiev Reservoir 1994 Dnieper River Pripyat River Data of UHMI Low part of Kiev Reservoir 137 Cs 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 Kiev Reservoir

After Chernobyl 137 Cs inventory in the 0-50 m layer increased by a factor of 6-10 and the total 137 Cs 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). 137 Cs input from the Danube and the Dnieper rivers (0.05 PBq in the period ) was insignificant in comparison with the short-term atmospheric fallout 137 Cs-137 in the Black Sea

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. 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 Food product, milk water external inhalation Actual dose Public perception about Dose realization (%) during a 70 years for children born in 1986 From I. Los, O. Voitsekhovych, 2001 For 1-st year about 47 % For 10 years about 80% Years Inadequate Radiation Risk Perception by Public was a key reason in WATER PROTECTION ACTION PLAN implementing