Radioecology of Cooling Pond Chernobyl NPP

   As it is known, methods of optimum blockage of radionuclide sources and their transport ways in water ecosystem are researched for reducing of population dose loads both in contaminated regions and far out of their ranges. The most perspective way for studying of radionuclide migration and accumulation in biotopes and reservoirs is ecosystem approach. But such way of study is complicated by large amount of representatives biotes and high circulation of closely interconnected abiotic and biotic processes in water ecosystem, so there are a few of works with consequent observance of ecosystem approach in radioecological studies. Probably, high cost of such study is played not last role here (special transport, attraction of specialists of different profile for long time, numerous sampling and high cost of analytical and cameral works. In majority of known works it was researched only one of water biota components and radionuclide concentration in water and bottom deposits during 1-2 vegetation seasons.

        

   Long-term various researches in the ChNPP cooling pond are executed by specialists of Chernobyl Research International Study Centre. Ecosystem researches in the upper shallow part of Kiev reservoir for several years were carried out by specialists of Hydrobiology Institute of NSA of Ukraine (Kiev).

   Fish population of the cooling pond for pre-accident period

  Fish population of the cooling pond for pre-accident period consisted of 33 species, which are referred to 7 families, where carp family (19 species) was noted as the largest species range. Other families (perch, cat-fish, pike and others) are presented by 1-2 species. Main part of fish quantity arrived in the cooling pond from Pripyat river and from its flood plain system during making of the reservoir, and some species canal sheat-fish, trout and others) were brought here in 1983-1985 for fish-breeding.
  In that time contaminated fish of ChNPP cooling pond mainly 137Cs and 144Ce, contents which beside different species found within 3-9,6 and 1,8-5,6 Бк/kgs accordingly. Concentration other radionuclides (134Cs, 65Zn, 58Co and others) usually did not exceed 2-2,6 Бк/kgs. <

   Radiation influence on ecosystem of the ChNPP cooling pond

   Zooplankton of the cooling pond is widespread freshwater species. The most greater variety amongst cancroid species was observed (Rotatoria), (Cladocera) and (Copepoda). At first years of zooplankton formation there are about 150 invertebrate species, but in consequence of CP usage their amount is reduced already to 1980 on 40 %.
   Zooplankton biomass of worm part of the reservoir was changed during vegetation period from 1,5 to 4,9 mg/l and with maximum level 11,5 mg/l. Before 1992 quantitative development of zooplankton stayed on, approximately, before accident level, and since 1993-1995 there had been its reduction, and presently, at average, it is 0,3-1 mg/l for vegetation period.
   Consequently, before accident and before 1992, the cooling pond was comparatively productive reservoir by zooplankton development. Its forage reserves have decreased noticeably next years. Reasons of reducing forage capacity of the cooling pond could be a high temperature of water, increased content of synthetic surface-active substances (SSAS) in water and salts of heavy metals, passing of plankton through cooling system of the plant and other reasons.
   Chronic influence of SSAS on zooplankton leads to reducing of its number (up to zero of Cladocera), to oppressing of reproduction and productivity ability during several generations. Danger of SSAS for cancroid species is caused also by mechanical pollution of filtration device by coarse dispersion particles and body charging, that leads to falling them on the reservoir bottom and destruction. Besides, SSAS change physical-chemical characteristics of reservoir surface layer and breaks natural aeration of water. Emulsion, forming with using of detergents, is very bad for water organisms.
   ChNPP exhaust waters content different salts of heavy metals, organic toxins and radionuclides, wich, also harms hydrobionts, in particular, phyto- and zooplankton.
   Radiation can not act ruinously on phyto- and zooplankton, because these groups of hydrobionts are much stable to ionising radiation. Mortal radiation dose for different water organisms are: 600 krad for protozoa, 120 krad for algaes, 20-109 krad for shellfishes, 1,5-56,6 krad for cancroid, 1,1-5,6 krad for fish. Many algaes species are capable to bear irradiating doses of 3-16 thousand rad and more, and for separate species mortal doses reached in experiments 1-2,5 mln. rad.
   Maximum dose received for vegetation period of 1986 is 3,65 rad. Comparison of this value with the lethal dose for algaes species does not raise doubts in absence of radiation harm action on phytoplankton. The same concerns zooplankton.

   Fish population of the cooling pond in post-accident period

  The investigation of fish contamination show (in 1998-2000) next level radioactive pollution (kBq/kgs).

• Pelecus cultratus   13,3
• Leuciscus cephalus   5,5
• Blicca bjoerkna   3,9
• Carassius auratus gibelio   8,3
• Abramis brama   5,0
• Scardinius erythrophthalmus   4,4
• Abramis sapa   5,0
• Rutilus rutilus   5,4
• Perca fluviatilis   27,0
• Silurus glanis   26,2
• Ictalurus punctatus   7,4
• Lucioperca lucioperca   21,2
• Esox lucius   24,5
• Cyprinus carpio   8,1

   Reference:


   Brisbin I.L et al. Accumulation and redistribution of radiocaesium by migratory waterfowl inhabbiting a reactor cooloing reservoir // In: Environmental behaviour of radionuclides released in the nuclear industry. Vienna: IAEA, 1973, p. 373-384.
   Rjabov I.N. Evaluation of radioactive contamination on ChNPP 30-km area hydrobionts // Radiobiology - 1992.- V. 32.- Iss. 5.- p. 662-667.
   Francevich L. I., Pan'kov I. V., Ermakov A. A. et al. Shellfishes are indicators of environment radionuclide contamination // Ecology, 1995, № 1, p. 57-62.
   Francevich L. I., Zaharchuk T. M., Klimashevsky O. A. et al. What can tell mollusc shells about? // The bulletin of ecological condition of exclusion zone, 1998, № 12 - p. 44-48.
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