radioACTIVE CONTAMINATION OF FISH in the Chernobyl NPP cooling pond during drawdown of water level

 

D. Gudkov¹, A. Kaglyan¹, K. Nanba², T. Wada², S. Kireev³, S. Obrizan³, L. Yurchuk¹

 

¹ Department of Aquatic Radioecology, Institute of Hydrobiology of the National Academy of Sciences of Ukraine, Kyiv, Ukraine

² Institute of Environmental Radioactivity, University of Fukushima, Fukushima, Japan

³ State Specialized Enterprise “Ecocentre”, Chernobyl, Ukraine

 

The Chernobyl NPP (CNPP) cooling pond (CP) is an artificial water body, located on the right bank floodplain area of the Pripyat River. The waterfront of the CP was formed partially by above the floodplain terrace, and preferably by protective dam with length of 25 km, width of 70-100 m and 5.7 m in height. Before the start of the drawdown of water level in the CP its length was 11 km, average width - 2 km, surface area - 22.7 km², prevailing depth - 4-7 m but on separate areas – up to 18-20 m and the amount of 149 million m³.

The CP is one of the most contaminated water bodies within the Chernobyl exclusion zone (CEZ). In May 1986 water radioactivity was determined mainly by ¹³¹I and other short-lived radionuclides and according to some sources was 1.5 kBq l^-1 [1], others - reached the order of 10⁵ Bq l^-1 [2]. The density of contamination of the CP's sediments by ⁹⁰Sr in early 1990s was 14.8 GBq km^-2 - 24.3 TBq km^-2 and ¹³⁷Cs - 0.4-28.4 TBq km^-2. In 2008, under the “Program of the ChNPP decommissioning”, it was decided on the CP drawdown. In late 2014, after the cessation of pumping water into the CP from the Pripyat River, the natural decline in the water level, mainly due to the filtering of water through the body of the dike, has begun.

This part of our studies was carried out during 2010-2018. The ¹³⁷Cs and ⁹⁰Sr concentration in water and fish was measured using by gamma-spectrometric and radiochemical methods. We studied 15 fish species of different ecological groups: pike (Esox lucius L.), zander (Sander lucioperca L.), perch (Perca fluviatilis L.), common rudd (Scardinius erythrophthalmus L.), common bleak (Alburnus alburnus L.), Prussian carp (Carassius gibelio Bloch), tench (Tinca tinca L.), common bream (Abramis brama L.), common roach (Rutilus rutilus L.), European carp (Cyprinus carpio L.), wels catfish (Silurus glanis L.), channel catfish (Ictalurus punctatus Raf.), asp (Leuciscus aspius L.), common chub (Squalius cephalus L.) and white bream (Blicca bjoerkna L.).

The decline of water level in the CP has caused a drastic change in the hydrological, hydrobiological and hydrochemical regime of aquatic ecosystem. In place of the CP three water bodies with different size and volume were formed. There was a mass death of periphyton communities of plants and animals (especially bivalves) and littoral aquatic plants. The declines of water level led to a significant decrease in spawning grounds, primarily for phytophilic and lithophilic fish species, whose representatives are one of the dominant groups in the ecosystem of the CP. Accordingly, the areas of feeding for the young of almost all species of fish have decreased, which in the future will significant reduce their quantity and biodiversity. During the period 2015-2018 the concentration of ⁹⁰Sr and ¹³⁷Cs in water increased by 35-45%.

Using the example of the north-western part of the CP (separated water body from 2015), it was established that the specific activity of ⁹⁰Sr and ¹³⁷Cs in fish during 2011–2014 there were, respectively, 40–359 (average 119±42) and 540–11270 (2473±1122) Bq/kg wet weight. The decrease in the water level in the CP caused a gradual increase in the ⁹⁰Sr concentration in fish, which by 2018 reached 184–959 Bq/kg (294±84); the specific activity of ¹³⁷Cs, at the same time, was at the level of 790–5070 Bq/kg (1865±960).

 

1.    S. V. Kazakov, P. S. Vovk, L. P. Fil’chagov  Radioecological state of the Chernobyl NPP cooling pond. Problems of the Chernobyl exclusion zone. 1, 129-138 (1994).

2.    I. I. Kryshev Radioactive contamination of aquatic ecosystems following the Chernobyl accident. J. Env. Radioactivity. 27, 207-219 (1995).