Accumulation of transuranic elements in the aquatic biota of the Belarusian sector of contaminated area near the Chernobyl nuclear power plant - Accumulation of transuranic elements in aquatic biota of Belarusian sector of contaminated area of Chernobyl nuclear power plant

The evolution of nuclear contamination of Belarus territory after Chernobyl accident includes the four stages: 1. Iodine-neptunium stage, caused mainly by short-lived radionuclides 131I, 239Np and others with a half-life period of several weeks; II. Intermediate stage, caused by radionuclides with a half-life period of a year (144Ce, 106Ru, 134Cs, etc.); III. Strontium-cesium stage, caused by 90Sr and 137Cs with a half-life period of about 30 years; IV. Plutonium-americium, caused by long-lived α-emitting radionuclides 241Am (period of half-life of 432 years) and 239+240Pu, having high radio and chemo-toxicity. According to forecasts, activity of 241Am to 2050 year will increase by 2.5 times and it will be the most important dose-related factor for the aquatic biota within the Chernobyl accident zone. In 2002 - 2008 years we have studied the accumulation of trans-uranic elements (TUE, 241Am, 239+240Pu) in basic components of water body ecosystems within the Chernobyl zone - non-flowing Perstok Lake, weak-flowing Borschevka flooding and small Braginka River. Among investigated components are water, bottom sediments, submerged macrophytes (Ceratophyllum submersum, Hydrocharis morsus-ranae, Lemna minor, Nuphar lutea, Stratiotes aloides), emergent macrophytes (Typha spp.), shellfish and fish. In the soil cover in the vicinity of the Perstok Lake activity of 241Am at present is equivalent to 300 - 600 Bq.kg-1, that is the basic source of its income to the lake. Radionuclides mobility in the water environment is higher than in the soil, that facilitates the rapid incorporation of 241Am to the trophic nets of water bodies and its removal by near-water animals in the terrestrial biotopes, including outside Chernobyl zone. Thus, the activity of 241Am in bottom sediments in the Perstok Lake and Borschevka flooding in 2008 year reach respectively 324 and 131 Bq.kg-1, and the activity of 241Am in macrophytes of the Perstok Lake at the same year was 1,0 - 3,7 Bq.kg-1. In summer period 2002 the activity of 241Am and 241Pu in the water of Perstok lake was 0,15 and 0,089 Bq.kg-1, and in the Braginka River - correspondingly 0,0044 and 0,16 Bq.l-1 Among the biota TUE maximum activity in 2002 was observed in emergent macrophytes of the Perstok Lake - up to 16 - 32 Bq.kg-1 on 239+240Pu and 5,7 - 20 on 241Am. TUE activity in emergent macrophytes was significantly lower - within 0,2 - 1,4 Bq.kg-1. Activity of TUE in submerge and emergent microphytes in Braginka River ranged within 0,12 - 1,8 B kg-1. Accumulation factors for 241Am (calculated for water) for macrophytes of the Prestok Lake were 1,3 - 130, and for 239+240Pu - 16 - 2000. Activity of TUE in fish and shellfish from the Perstok Lake in 2002 was lower than on macrophytes correspondingly 0,35 and 0,25 Bq.kg-1. With its half-life and mobility in water environment, TUE will be accumulated in stagnant water bodies and activated through trophic chains to the cycling of matter. Over the next centuries will represent radiological danger for aquatic biota. Therefore, the further investigations of dynamics of TUE accumulation by biota and their resulted biological effects are very urgent. (authors)